VENDELINUS ASTRONOMY NEWSLETTER ------------------------------- Erwin Verwichte, April 2006 (Erwin.Verwichte@warwick.ac.uk) http://www.warwick.ac.uk/go/erwin_verwichte CONTENTS 1. SOLAR SYSTEM * Reiner Gamma swirl: magnetic effect of a cometary impact? * Mercury's formation impact splattered Earth with material * Unexpected detail in first-ever Venus south pole images * Mars Express's OMEGA uncovers possible sites for life * First Color HiRISE Image of Mars * Prometheus and its Pull on the Passing Particles of Saturn's F Ring * Blue ring discovered around Uranus * The Comet With a Broken Heart * Fragmenting Comet Won't Hit Earth * Hubble Finds "Tenth Planet" is Slightly Larger Than Pluto 2. ASTROPHYSICS * Synergy of Technologies Reveal Origin of Dust Around Nearby Star * ESA's ISO provides the first view of monstrous stars being born * Cosmic Spider is Good Mother * Upgraded MERLIN Spies Cloud of Alcohol Spanning 288 Billion Miles * Eta Carinae: A Spectacular Show From A Convulsing Massive Star * Exploding 'Star Within A Star' * XMM-Newton reveals a tumbling neutron star * NASA's Spitzer Finds Hints of Planet Birth Around Dead Star * NASA Achieves Breakthrough in Black Hole Simulation * Deadly astronomical event not likely to happen in our galaxy, study finds * Unravelling a cosmic mystery - Scientists discover the Universe's strongest magnetic field * Hubble's view of Cigar Galaxy on sixteenth mission anniversary * The universe trapped in its own web * The Search For The History Of The Universe's Light Emission * Galaxy simulation breaks new ground 3. SPACE MISSIONS * New and Improved Antimatter Spaceship for Mars Missions * NASA Mars Rovers Head for New Sites After Studying Layers * Europe scores new planetary success: Venus Express enters orbit around the Hothouse Planet * New NASA Ames Spacecraft to Look for Ice at Lunar South Pole * Asteroids: treasures of the past and a threat to the future 1. SOLAR SYSTEM _______________ * Reiner Gamma swirl: magnetic effect of a cometary impact? ----------------------------------------------------------- (ESA Press Release, April 6th, 2006) (http://www.esa.int/esaSC/SEM05FNFGLE_index_0.html) This image, made from images taken by the Advanced Moon Imaging Experiment (AMIE) on board ESA's SMART-1 spacecraft, shows a feature characterised by bright albedo, and called Reiner Gamma Formation. The Reiner Gamma Formation, a totally flat area consisting of much brighter material than the surrounding dark 'mare', is centred on an area located at 57.8 degrees West, 8.1 degrees North, in the Oceanus Procellarum on the near (visible) side of the Moon, and has an extension of approximately 30 by 60 kilometres. The AMIE camera obtained the images on 14 January 2006, from a distance between 1599 and 1688 kilometres and with a ground resolution between 144 and 153 metres per pixel. From early ground-based observations, this feature was initially misidentified as a crater. Only later detailed observations from orbit (such as those performed by USSR's Zond-6, and NASA's Lunar Orbiter, Apollo and Clementine missions) revealed its true nature: a very unusual morphology, consisting of swirl-like patterns that do not correspond to any topographic features. Its main part consists of a bright pattern of elliptical shape, located to the west of Reiner crater. Bright elongated patches extend to the northeast in the Marius Hills region and small swirls extend to the southwest. The origin of the Reiner Gamma Formation and other swirls occurring on the lunar surface is still unclear. Lunar swirls are associated with magnetic anomalies and some of these swirls such as Mare Ingenii and Mare Marginis - are 'antipodal' to large impact structures (that is they are located right into opposite regions of the Moon globe). So, it was suggested that the Reiner Gamma swirls correspond to magnetised materials in the crust or iron-rich ejecta materials able to deflect the solar wind (constant flow of charged particles coming from the Sun). This would prevent surface materials to undergo maturation processes, and so produce an optical anomaly. However, Reiner Gamma Formation still stands as a particular case. In fact, the magnetic anomaly does not correlate with the scale of the lunar crust structure and large-scale anomalies seen on the far side. Furthermore, the anomaly is not associated with any obvious antipodal basin structure, and the surface material related to Reiner Gamma appears optically very immature (the age for its emplacement could be quite recent). The analysis of NASA's Clementine imaging data showed that the optical and spectroscopic properties of the local regolithic surface layer are close to those of immature mare crater-like soils. This is consistent with the properties of a shallow subsurface mare soil layer. Considerations from works on impact cratering support the hypothesis that the uppermost part of the regolith could have been modified through an interaction with falling fragments of a low-density comet nucleus, previously broken by tidal forces and having ploughed the regolith. Then, the magnetic anomaly would not be the result of an antipodal crustal field generated in the formation process of large impact basins. It would rather arise from local effects during the interaction between the lunar surface and cometary physical environment, with the possibility that the solar wind is locally deflected and contributes to the unusual optical properties. So, the Reiner Gamma Formation could be an interesting site for future human exploration because of the radiation deflected from the surface. Further testing of this hypothesis requires access to the physical properties of the surface to constrain the mechanisms of formation of the lunar swirls. This is an ongoing task for the AMIE camera, aimed at studying regolith photometric properties. * Mercury's formation impact splattered Earth with material ----------------------------------------------------------- (RAS Press Release, April 5th, 2006) (http://www.ras.org.uk/index.php?option=com_content&task=view&id=982&Itemid=2) New computer simulations of Mercury's formation show the fate of material blasted out into space when a large proto-planet collided with a giant asteroid 4.5 billion years ago. The simulations, which track the material over several million years, shed light on why Mercury is denser than expected and show that some of the ejected material would have found its way to the Earth and Venus. "Mercury is an unusually dense planet, which suggests that it contains far more metal than would be expected for a planet of its size. We think that Mercury was created from a larger parent body that was involved in a catastrophic collision, but until these simulations we were not sure why so little of the planet's outer layers were reaccreted following the impact," said Dr Jonti Horner, who is presenting results at the Royal Astronomical Society's National Astronomy Meeting on 5th April. To solve this problem, Dr Horner and his colleagues from the University of Bern ran two sets of large-scale computer simulations. The first examined the behaviour of the material in both the proto-planet and the incoming projectile; these simulations were among the most detailed to date, following a huge number of particles and realistically modelling the behaviour of different materials inside the two bodies. At the end of the first simulations, a dense Mercury-like body remained along with a large swathe of rapidly escaping debris. The trajectories of the ejected particles were then fed in to a second set of simulations that followed the motion of the debris for several million years. Ejected particles were tracked until either they landed on a planet, were thrown into interstellar space, or fell into the Sun. The results allowed the group to work out how much material would have fallen back onto Mercury and investigate other ways in which debris is cleared up in the Solar System. The group found that the fate of the debris depended on whereabouts Mercury was hit, both in terms of its orbital position and in terms of the angle of the collision. Whilst purely gravitational theory suggested that a large fraction of the debris would eventually fall back onto Mercury, the simulations showed that it would take up to 4 million years for 50 percent of the particles to land back on the planet and in this time many would be carried away by solar radiation. This explains why Mercury retained a much smaller proportion than expected of the material in its outer layers. The simulations also showed that some of the ejected material made its way to Venus and the Earth. While this is only a small fraction, it illustrates that material can be transferred between the inner planets relatively easily. Given the amount of material that would have been ejected in such a catastrophe, it is likely that there is a reasonable amount (possibly as much as 16 million billion tonnes [1.65x10^19 kg]) of proto-Mercury in the Earth. * Unexpected detail in first-ever Venus south pole images --------------------------------------------------------- (ESA Press Release, May 7th, 2006) (http://www.esa.int/esaCP/SEM9FZNFGLE_index_0.html) ESA's Venus Express has returned the first-ever images of the hothouse planet's south pole from a distance of 206 452 kilometres, showing surprisingly clear structures and unexpected detail. The images were taken 12 April during the spacecraft's initial capture orbit after successful arrival on 11 April 2006. Engineers have lost no time in switching on several of the instruments and yesterday the VMC (Venus Monitoring Camera) and VIRTIS (Visible and Infrared Thermal Imaging Spectrometer) imaged, for the first time in space history, the southern hemisphere of Venus as the spacecraft passed below the planet in an elliptical arc. Scientists are especially intrigued by the dark vortex shown almost directly over the south pole, a previously suspected but until now unconfirmed structure that corresponds to a similar cloud structure over the north pole. "Just one day after arrival, we are already experiencing the hot, dynamic environment of Venus," said Dr Hakan Svedhem, Venus Express project scientist. "We will see much more detail at an unprecedented level as we get over 100 times better resolution as we get closer to Venus, and we expect to see these spiral structures evolve very quickly." The initial, low-quality images were taken from an extreme distance of 206 452 kms from the planet, yet caught scientists' attention, particularly with the surprisingly clear structures and unexpected details shown in the VIRTIS spectrometer images. * Mars Express's OMEGA uncovers possible sites for life ------------------------------------------------------- (ESA Pres Release, April 20th, 2006) (http://www.esa.int/esaCP/SEM117OFGLE_index_0.html) By mapping minerals on the surface of Mars using the European Space Agency's Mars Express spacecraft, scientists have discovered key minerals that allow to characterise three ages of Martian geological history as reported in today's issue of Science - and found valuable clues as to where life may have developed. The new work shows that large bodies of standing water might only have been present on Mars in the remote past, before four thousand million years ago, if they were present at all. Within half a billion years, these conditions had faded away. The results come from the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on board Mars Express. In one Martian year (687 Earth days) of operation, OMEGA mapped 90 percent of the surface, allowing the identification of a variety of minerals and the processes by which they have been altered during the course of Martian history. The maps have allowed a team of scientists, led by Professor Jean-Pierre Bibring, Institut d'Astrophysique Spatiale (IAS), Orsay (France), to characterise three geological eras for Mars. The earliest, named by the authors as the 'phyllosian' era, would have occurred between 4.54.2 thousand million years ago, soon after the planet formed. The environment was possibly warm and moist at this time, allowing the formation of large-scale clay beds, many of which survive today. The second era, the 'theiikian', would have taken place between 4.2 and 3.8 billion years ago. It was prompted by planet-wide volcanic eruptions that drove global climate change. In particular, the sulphur these eruptions belched into the atmosphere reacted with the water to produce acid rain, which altered the composition of the surface rocks where it fell. Finally, there was the 'siderikian', the longest lasting of the Martian eras. It would have begun sometime around 3.83.5 billion years ago and continues today. There is little water involved in this era; instead, the rocks appear to have been altered during slow weathering by the tenuous Martian atmosphere. This process gave Mars its red colour. The eras are named after the Greek words for the predominant minerals formed within them. The one most likely to have supported life was the phyllosian, when clay beds could have formed at the bottom of lakes and seas, providing the damp conditions in which the processes of life could begin. However, there are still question marks. The team points out that the clay beds might have been formed underground, rather than in lakebeds. "Hydrothermal activity below the surface, the impact of water-bearing asteroids, even the natural cooling of the planet could all have promoted the formation of clay below Mars's surface. If so, the surface conditions may always have been cold and dry," said Bibring. After this initial period, water largely disappeared from the planet's surface either by seeping underground or being lost into space. Except for a few localised transient water events, Mars became the dry, cold desert seen by spacecraft today. This new identification of clay beds on Mars provides high-priority targets for future Mars landers that seek to investigate whether Mars once harboured life. "If living organisms formed, the clay material would be where this biochemical development took place, offering exciting places for future exploration because the cold Martian conditions could have preserved most of the record of biological molecules up to the present day," concluded Bibring. * First Color HiRISE Image of Mars ---------------------------------- (NASA News, April 7th, 2006) (http://www.nasa.gov/mission_pages/MRO/multimedia/pia08061.html) This is the first color image of Mars from the High Resolution Imaging Science Experiment on NASA's Mars Reconnaissance Orbiter. At the center portion of the camera's array of light detectors there are extra detectors to image in green and near-infrared color bandpasses, to be combined with the black-and-white images (from red-bandpass detectors) to create color images. This is not natural color as seen by human eyes, but infrared color -- shifted to longer wavelengths. This image also has been processed to enhance subtle color variations. The southern half of the scene is brighter and bluer than the northern half, perhaps due to early-morning fog in the atmosphere. Large-scale streaks in the northern half are due to the action of wind on surface materials. The blankets of material ejected from the many small fresh craters are generally brighter and redder than the surrounding surface, but a few are darker and less red. Two greenish spots in the middle right of the scene may have an unusual composition, and are good future targets for the Compact Reconnaissance Imaging Spectrometer for Mars, a mineral-identifying instrument on Mars Reconnaissance Orbiter ( http://crism.jhuapl.edu/). In the bottom half of the image we see a redder color in the rough areas, where wind and sublimation of water or carbon dioxide ice have partially eroded patches of smooth-textured deposits. This image was taken by HiRISE on March 24, 2006. The image is centered at 33.65 degrees south latitude, 305.07 degrees east longitude. It is oriented such that north is 7 degrees to the left of up. The range to the target was 2,493 kilometers (1,549 miles). At this distance the image scale is 2.49 meters (8.17 feet) per pixel, so objects as small as 7.5 meters (24.6 feet) are resolved. In total this image is 49.92 kilometers (31.02 miles) or 20,081 pixels wide and 23.66 kilometers (14.70 miles) or 9,523 pixels long. The image was taken at a local Mars time of 07:33 and the scene is illuminated from the upper right with a solar incidence angle of 78 degrees, thus the sun was 12 degrees above the horizon. At an Ls of 29 degrees (with Ls an indicator of Mars' position in its orbit around the sun), the season on Mars is southern autumn. Images from the High Resolution Imaging Science Experiment and additional information about the Mars Reconnaissance Orbiter are available online at: http://www.nasa.gov/mro or http://HiRISE.lpl.arizona.edu. For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. * Prometheus and its Pull on the Passing Particles of Saturn's F Ring --------------------------------------------------------------------- (RAS Press Release, April 4th, 2006) (http://www.ras.org.uk/index.php?option=com_content&task=view&id=974&Itemid=2) The rings around all the giant planets in our Solar System are thought to be stabilised by small 'shepherd moons' that orbit in or near the rings and stabilize them by gravitational influences. The narrow F ring of Saturn which lies just outside the spectacular main rings - is tended by two small shepherds. Prometheus (100 km in diameter) orbits just inside the F ring, while Pandora (85 km in diameter) moves around Saturn just outside the F ring. Periodic structures such as azimuthal gaps 'channels' of low optical depth - and 'streamers' have been discovered. These features can be seen in Movie1. The origin of these features has been explored by a team at Queen Mary, University of London (QMUL) using numerical integrations. On Tuesday 4 April, Carlos Chavez of QMUL will be explaining to the RAS National Astronomy Meeting in Leicester the results of their computer models, which explain the close and complex relationship between Prometheus and the tangled F ring. "The models are in excellent agreement with structures observed in the Cassini images," said Chavez. "We have found that the gaps are not due to a lack of particles, but to a forced change in orbital elements by a close encounter with Prometheus," he explained. "The moon's gravity temporarily pulls some of the particles away from the main stream as it passes by." "It is like a crowd of people walking in a number of lines in the same direction down a street. Suddenly, someone else comes from the other side of the street and collides with a few of them. He then tells them to come with him, and walks away. Only people in the closest lines follow him, which produces gaps in the crowd. However, they return back to the main group shortly afterwards." The most dramatic case will happen in late 2009, when the F ring and Prometheus are anti-aligned. Once per orbit during this anti-alignment Prometheus will be at apoapsis (its furthest point from Saturn) and the nearby ring particles will be at periapsis (closest point to Saturn). At that time, Prometheus and the ring particles are at their closest to each other. the ring particles and Prometheus. They found a low number of collisions - only 0.6 percent of the particles collided per orbit. This was unexpected, since it was originally thought that Prometheus is a 'thieving moon', stealing particles from the F ring. What actually happens is that the particles are only temporarily pulled away and then drift back into the ring. The ring-moon interactions are also likely to have an effect on the surface of Prometheus. Like our Moon and most other planetary satellites, Prometheus has a synchronous rotation, always showing the same face to Saturn. The team at QMUL investigated the location on Prometheus' surface where the particles would be expected to collide. They found that, in the synchronous co-rotating reference frame, the collisions surprisingly occurred on the trailing face of Prometheus, and preferably in the equatorial region. This scenario has important implications for the surface features of Prometheus, and the team expects to find differences in albedo (reflectivity) between the trailing and leading faces. "It would be like a man colliding with other people while facing continuously in a particular direction and hitting them with only one side of his body," said Chavez. * Blue ring discovered around Uranus ------------------------------------ (UCBerkeley News, April 6th, 2006) (http://www.berkeley.edu/news/media/releases/2006/04/06_bluering.shtml) The outermost ring of Uranus, discovered just last year, is bright blue, making it only the second known blue ring in the solar system, according to a report this week in the journal Science. Perhaps not coincidentally, both blue rings are associated with small moons. "The outer ring of Saturn is blue and has Enceladus right smack at its brightest spot, and Uranus is strikingly similar, with its blue ring right on top of Mab's orbit," said Imke de Pater, professor of astronomy at the University of California, Berkeley. "The blue color says that this ring is predominantly submicron-sized material, much smaller than the material in most other rings, which appear red." The authors of the paper in the April 7 issue of Science are de Pater, Mark Showalter of the SETI Institute in Mountain View, Calif.; Heidi B. Hammel of the Space Science Institute in Boulder, Colo.; and Seran Gibbard of Lawrence Livermore National Laboratory in California. The similarity between these outer rings implies a similar explanation for the blue color, according to the authors. Many scientists now ascribe Saturn's blue E ring to the small dust, gas and ice particles spewed into Enceladus' orbit by newly discovered plumes on that moon's surface. However, this is unlikely to be the case with Mab, a small, dead, rocky ball, about 15 miles across - one-twentieth the diameter of Enceladus. Instead, the astronomers suspect both rings owe their blue color to subtle forces acting on dust in the rings that allow smaller particles to survive while larger ones are recaptured by the moon. "We know now that there is at least one way to make a blue ring that doesn't involve plumes, because Mab is surely too small to be internally active," said Showalter. He and astronomer Jack Lissauer of NASA Ames Research Center in Mountain View, Calif., discovered Mab in Hubble Space Telescope images in 2003. The likely scenario to explain Saturn's blue ring was proposed before plumes were discovered last November as the Cassini spacecraft flew by Enceladus. As modeled for the E ring, meteoroid impacts on the surface of Enceladus scatter debris into its orbit, probably in a broad range of sizes. While the larger pieces remain within the moon's orbit and eventually are swept up by the moon, smaller particles are subject to subtle forces that push them toward or away from the planet out of the moon's orbit. These forces include pressure from sunlight, magnetic torques acting on charged dust particles, and the influence of slight variations in gravity due to the equatorial bulge of Saturn. The net result is a broad ring of smaller particles, most less than a tenth of a micron across - a thousandth the width of a human hair - that scatter and reflect predominantly blue light. "This model can be transferred directly to what we now see in Uranus, although we still need to understand the details of the process," de Pater said. All other rings - those around Jupiter, Saturn, Uranus and Neptune - are reddish. Though they contain particles of many sizes that reflect many wavelengths of light, red dominates not only because larger particles - many microns to meters across - are abundant, but also because the material itself may be reddish, perhaps from iron. "Arguing by analogy, the two outermost rings, the two rings that have satellites embedded in them, are both the blue rings. That can't be coincidental, there has to be a common thread of dynamics that is causing both of these phenomena," Showalter said. The discovery of the blue ring came after combining ground-based near-infrared observations by the Keck Telescope in Hawaii and visible-light photos taken by the Hubble Space Telescope. De Pater, Hammel and Gibbard have observed Uranus since 2000 with the second-generation NIRC2 infrared camera using the adaptive optics system on the Keck II telescope, and in August 2005 obtained 30 new images of the planet in hopes of seeing new features as the ring plane moves edge-on to Earth. Showalter and Lissauer, on the other hand, captured numerous visible-light images of Uranus between 2003 and 2005 with Hubble's Advanced Camera for Surveys. Neither team realized it had captured pictures of new rings until an extensive analysis, basically piling image upon image until faint features stood out from the background. In December 2005, as Showalter and Lissauer reported finding two new rings - Uranus's 12th and 13th - and two new moons, Mab and Cupid, numbers 26 and 27, de Pater, Hammel and Gibbard reported seeing the red, innermost of the two new rings but not the outermost. The blue ring peaks in brightness about 97,700 kilometers from the planet's center, exactly at Mab's orbit. Further analysis proved to both teams that the outer ring seen in visible light was definitely not observable in the near-infrared, and so must be blue. The analysis also showed that Mab, which like its ring could not be seen in the infrared, is probably covered with water ice, like the other outer moons of Uranus, and is probably Uranus's smallest moon. * The Comet With a Broken Heart ------------------------------- (ESO Press Release, April 25th, 2006) (http://www.eso.org/outreach/press-rel/pr-2006/pr-15-06.html) On the night of April 23 to 24, ESO's Very Large Telescope observed fragment B of the comet Schwassmann-Wachmann 3 that had split a few days earlier. To their great surprise, the ESO astronomers discovered that the piece just ejected by fragment B was splitting again! Five other mini-comets are also visible on the image. The comet seems thus doomed to disintegrate but the question remains in how much time. Comet 73P/Schwassmann-Wachmann 3 (SW 3) is a body with a very tormented past. This comet revolves around the Sun in about 5.4 years, in a very elongated orbit that brings it from inwards of the Earth's orbit to the neighbourhood of giant planet Jupiter. In 1995, when it was coming 'close' to the Earth, it underwent a dramatic and completely unexpected, thousand-fold brightening. Observations in 1996, with ESO's New Technology Telescope and 3.6-m telescope, at La Silla, showed that this was due to the fact that the comet had split into three distinct pieces. Later, in December 1996, two more fragments were discovered. At the last comeback, in 2001, of these five fragments only three were still seen, the fragments C (the largest one), B and E. No new fragmentations happened during this approach, apparently. Things were different this time, when the comet moved again towards its closest approach to the Sun - and to the Earth. Early in March, seven fragments were observed, the brightest (fragment C) being of magnitude 12, i.e. 250 fainter than what the unaided can see, while fragment B was 10 times fainter still. In the course of March, 6 new fragments were seen. Early in April, fragment B went into outburst, brightening by a factor 10 and on 7 April, six new fragments were discovered, confirming the high degree of fragmentation of the comet. On 12 April, fragment B was as bright as the main fragment C, with a magnitude around 9 (16 times fainter than what a keen observer can see with unaided eyes). Fragment B seems to have fragmented again, bringing the total of fragments close to 40, some being most probably very small, boulder-sized objects with irregular and short-lived activity. The new observations reveal that this new small fragment has split again! The image clearly reveals that below the main B fragment, there is a small fragment that is divided into two and a careful analysis reveals five more tiny fragments almost aligned. Thus, this image alone shows at least 7 fragments. The comet has thus produced a whole set of mini-comets! Will the process continue? Will more and more fragments form and will the comet finally disintegrate? How bright will the fragments be when the comet will be the closest to the Earth, on 11 to 14 May, and how many new fragments will have appeared before the comet reaches its closest approach to the Sun, around 7 June? \^^ comet.jpg Image of Fragment B and associated mini-comets. This is a digitally-enhanced zoom-in version of PR Photo 15b/06 to show in a better way some of the smaller fragments. An arrow indicates the fragments that could be seen, including the main one - on top, the two just below that have just split and five others, much dimmer. Fragment C of the comet should be the closest to Earth on 11 May, when it will be about 12 million km away, while fragment B will come as 'close' as 10 million km from Earth on 14 May. Although this is the closest a comet ever approached Earth in more than twenty years - even Comet Hyakutake's smallest distance was 15 million km - this is still 26 times the distance between the Earth and the Moon and therefore does not pose any threat to our planet. If nothing else happens, at the time of closest approach, fragment B will be just visible with unaided eye by experienced observers. It should be an easy target however to observe with binoculars. If we are lucky, however, fragment B presents another outburst, becoming a magnificent sight in the night sky. On the other hand, it could just as well fade away into oblivion. But then, the main fragment C should still be visible, even possibly with the unaided eye. ESO telescopes will observe the comet in the greatest detail at the end of May, when it is best observed from Chile and is brighter. These observations will obtain invaluable information, especially as the fragmentation process is revealing all the pristine material buried below the crust of the comet. As such, these observations will prove an ideal complement to the most comprehensive observation campaign made with ESO telescopes of Comet Tempel 1 when it was being bombarded by the Deep Impact spacecraft, on 4 July 2005. * Fragmenting Comet Won't Hit Earth ----------------------------------- (NASA News, April 27th, 2006) (http://www.nasa.gov/mission_pages/hubble/Comet_73P.html) There will be no tsunamis, firestorms or mass extinctions to spoil your Memorial Day weekend. Although the Internet is rife with speculation that a fragment of Comet 73P/Schwassmann-Wachmann 3 will strike the Earth on May 25, neither the main comet nor any of its more than 40 fragments pose a danger to Earth. "We are very well acquainted with the trajectory of Comet 73P Schwassmann-Wachmann 3," said Donald Yeomans, manager of NASA's Near-Earth Object Program Office. "There is absolutely no danger to people on the ground or the inhabitants of the International Space Station, as the main body of the object and any pieces from the breakup will pass many millions of miles beyond the Earth." However, you can see the comet falling apart right before our eyes, thanks to NASA's Hubble Space Telescope. Recent Hubble images have uncovered many more fragments than have been reported by ground-based observers. These observations provide an unprecedented opportunity to study the demise of a comet nucleus. None of the comet's fragments will come closer than 5.5 million miles to Earth during its closest approaches May 12 - 28. That's more than 20 times the distance from the Earth to the moon. The main fragment, designated fragment C, will pass closest to Earth on May 12 at a distance of approximately 7.3 million miles. It will be visible to small telescopes during the morning hours in the constellation Vulpecula. NASA's Spitzer Space Telescope will observe the comet in May. Astronomers have been observing the comet for more than 75 years. The trajectory of this comet has been monitored and refined over time, and its path around the sun is well understood. Amateur and professional astronomers around the world have been tracking its spectacular disintegration for years. The comet is currently comprised of a chain of fragments, named alphabetically, stretching across several degrees on the sky. (The sun and moon each have an apparent diameter of about 1/2 of a degree.) Ground-based observers have noted dramatic brightening events associated with some of the fragments (as seen in the image below) indicating that they are continuing to break-up and that some may disappear altogether. Hubble caught two of the fragments, B and G, shortly after large outbursts in activity. Hubble also photographed fragment C , which at the time was less active. The resulting images reveal that a hierarchical destruction process is taking place, in which fragments are continuing to break into smaller chunks. Several dozen "mini-fragments" are found trailing behind each main fragment, probably associated with the ejection of house-sized chunks of surface material that can only be detected in these very sensitive and high- resolution Hubble images. Sequential Hubble images of the B fragment, taken a few days apart, suggest that the chunks are pushed down the tail by outgassing from the icy, sunward-facing surfaces of the chunks, much like space-walking astronauts are propelled by their jetpacks. The smaller chunks have the lowest mass, and so are accelerated away from the parent nucleus faster than the larger chunks. Some of the chunks seem to dissipate completely over the course of several days. Deep-freeze relics of the early solar system, cometary nuclei are porous and fragile mixes of dust and ices. They can be broken apart by gravitational tidal forces when they pass near large bodies. For example, Comet Shoemaker-Levy 9 was torn to pieces when it skirted near Jupiter in 1992, prior to plunging into Jupiter's atmosphere two years later. They can also fly apart from rapid rotation of the nucleus, break apart because of thermal stresses as they pass near the Sun, or explosively pop apart like corks from champagne bottles due to the outburst of trapped volatile gases. "Catastrophic breakups may be the ultimate fate of most comets," says planetary astronomer Hal Weaver of the Johns Hopkins University Applied Physics Laboratory, who led the team that made the recent Hubble observations and who used Hubble previously to study the fragmentations of comets Shoemaker-Levy 9 in 1993-1994, Hyakutake in 1996, and 1999 S4 (LINEAR) in 2000. Analysis of the new Hubble data, and data taken by other observatories as the comet approaches the Earth and Sun, may reveal which of these breakup mechanisms are contributing to the disintegration of 73P/Schwassmann-Wachmann 3. German astronomers Arnold Schwassmann and Arno Arthur Wachmann discovered this comet during a photographic search for asteroids in 1930, when the comet passed within 5.8 million miles of the Earth (only 24 times the Earth-Moon distance). The comet orbits the Sun every 5.4 years, but it was not seen again until 1979. The comet was missed again in 1985 but has been observed every return since then. During the fall of 1995, the comet had a huge outburst in activity and shortly afterwards four separate nuclei were identified and labeled "A", "B", "C", and "D", with "C" being the largest and the presumed principal remnant of the original nucleus. Only the C and B fragments were definitively observed during the next return, possibly because of the poor geometry for the 2000-2001 apparition. The much better observing circumstances during this year's return may be partly responsible for the detection of so many new fragments, but it is also likely that the disintegration of the comet is now accelerating. Whether any of the many fragments will survive the trip around the Sun remains to be seen. * Hubble Finds "Tenth Planet" is Slightly Larger Than Pluto ----------------------------------------------------------- (NASA News, April 11th, 2006) (http://www.nasa.gov/home/hqnews/2006/apr/HQ_06183_hubble_tenth_planet.html) For the first time, NASA's Hubble Space Telescope has seen distinctly the "tenth planet," currently nicknamed "Xena," and has found that it is only slightly larger than Pluto. Though previous ground-based observations suggested that Xena's diameter was about 30 percent greater than Pluto, Hubble observations taken Dec. 9 and 10, 2005, showed Xena's diameter as 1,490 miles (with an uncertainty of 60 miles). Pluto's diameter, as measured by Hubble, is 1,422 miles. "Hubble is the only telescope capable of getting a clean visible-light measurement of the actual diameter of Xena," said Mike Brown, planetary scientist at the California Institute of Technology in Pasadena, Calif. Brown's research team discovered Xena, officially cataloged as 2003 UB313, and its results have been accepted for publication in the Astrophysical Journal. Only a handful of images were required to determine Xena's diameter. Located 10 billion miles from Earth with a diameter a little more than half the width of the United States, the object is 1.5 pixels across in Hubble's view. That's enough to make a precise size measurement. Because Xena is smaller than previously thought, but comparatively bright, it must be one of the most reflective objects in the solar system. The only object more reflective is Enceladus, a geologically active moon of Saturn whose surface is continuously recoated with highly reflective ice by active geysers. Xena's bright reflectivity is possibly due to fresh methane frost on its surface. The object may have had an atmosphere when it was closer to the sun, but as it moved to its current location farther away this atmosphere would have "frozen out," settling on the surface as frost. Another possibility is that Xena leaks methane gas continuously from its warmer interior. When this methane reaches the cold surface, it immediately freezes solid, covering craters and other features to make it uniformly bright to Hubble's telescopic eye. Xena's takes about 560 years to orbit the sun, and it is now very close to aphelion (the point on its orbit that is farthest from the sun).Brown next plans to use Hubble and other telescopes to study other recently discovered Kuiper Belt objects that are almost as large as Pluto and Xena. The Kuiper Belt is a vast ring of primordial icy comets and larger bodies encircling Neptune's orbit. Finding that the largest known Kuiper Belt object is a virtual twin to Pluto may only further complicate the debate about whether to categorize the large icy worlds that populate the belt as planets. If Pluto were considered to be the minimum size for a planet, then Xena would fulfill this criterion, too. In time, the International Astronomical Union will designate the official name. 2. ASTROPHYSICS _______________ * Synergy of Technologies Reveal Origin of Dust Around Nearby Star ------------------------------------------------------------------ (Subaru Telescope Press Release, April 20th, 2006) (http://subarutelescope.org/Pressrelease/2006/04/20/index.html) Beta Pictoris as a Laboratory for Planet Formation Planets form in disks of gas and dust that surround new born stars. Such disks are called proto-planetary disks. The dust in these disks become rocky planets like Earth and the inner cores of giant gas planets like Saturn. This dust is also a repository of elements that form the basis of life. Proto-planetary disks disappear as stars mature, but many stars have what are called debris disks. Astronomers hypothesize that once objects such as asteroids and comets are born from the proto-planetary disk, collisions among them can produce a secondary dust disk. The most well-known example of such dust disks is the one surrounding the second brightest star in the constellation Pictor, meaning "painter's easel". This star, known as Beta Pictoris or Beta Pic, is a very close neighbor of the Sun, only sixty light years away, and therefore easy to study in great detail. Beta Pic is twice as bright as the Sun, but the light from the disk is much fainter. Astronomers Smith and Terrile were the first to detect this faint light in 1984, by blocking the light from the star itself using a technique called coronagraphy. Since then, many astronomers have observed the Beta Pic disk using ever better instruments and ground and space-based telescopes to understand in detail the birth place of planets, and hence life. Combining Technologies A team of astronomers from the National Astronomical Observatory of Japan, Nagoya University and Hokkaido University combined several technologies for the first time to obtain an infrared polarization image of the Beta Pic disk with better resolution and higher contrast than ever before: a large aperture telescope (the Subaru telescope, with its large 8.2 meter primary mirror), adaptive optics technology, and a coronagraphic imager capable of taking images of light with different polarizations (Subaru's Coronagraphic Imager with Adaptive Optics,CIAO). A large aperture telescope, especially with Subaru's great imaging quality, allows faint light to be seen at high resolution. Adaptive optics technology reduces Earth's atmosphere's distorting effects on light, allowing higher resolution observations. Coronagraphy is a technique for blocking light from a bright object such as a star, to see fainter objects near it, such as planets and dust surrounding a star. By observing polarized light, reflected light can be distinguished from light coming directly from its original source. Polarization also contains information about the size, shape, and alignment of dust reflecting light. With this combination of technologies, the team succeeded in observing Beta Pic in infrared light two micrometers in wavelength at a resolution of a fifth of an arcsecond. This resolution corresponds to being able to see an individual grain of rice from one mile away or a mustard seed from a kilometer away. Achieving this resolution represents a huge improvement over comparable previous polarimetric observations from the 1990's that had only resolutions of about one and a half arcseconds. Collisions of Planetesimals and Bacteria-Size Dust Bunnies The new results strongly suggest that Beta Pic's disk contains planetesimals, asteroid or comet-like objects, that collide to generate dust that reflects starlight. The polarization of the light reflected from the disk can reveal the physical properties of the disk such as composition, size, and distribution. An image of all the two micrometer wavelength light shows the long thin structure of the disk seen nearly edge on. The polarization of the light shows that ten percent of the two micrometer light is polarized. The pattern of polarization indicates that the light is a reflection of light that originated from the central star. An analysis of how the brightness of the disk changes with distance from the central shows a gradual decrease in brightness with a small oscillation. The slight oscillation in brightness corresponds to variations in the density of the disk. The most likely explanation is that denser regions correspond to where planetesimals are colliding. Similar structures have been seen closer to the star in earlier observations at longer wavelengths using Subaru's COoled Mid-Infrared Camera and Spectrograph (COMICS) and other instruments. A similar analysis of how the amount of polarization changes with distance from the star shows a decrease in polarization at a distance of one hundred astronomical units (an astronomical unit is the distance between Earth and the Sun). This corresponds to a location where the brightness also decreases, suggesting that at this distance from the star there are fewer planetesimals. The light is polarized by about 10 percent. As the team investigated models of the Beta Pic disk that can explain both the new and old observations, they found that the dust in Beta Pic's disk is more than ten times larger than typical grains of interstellar dust. Beta Pics dust disk is probably made of micrometer sized loose clumps of dust and ice like miniscule bacteria-size dust bunnies. Together, these results provide very strong evidence that the disk surrounding Beta Pic is generated by the formation and collision of planetesimals. The level of detail of this new information solidifies our understanding of the environment in which planets form and develop. Motohide Tamura who leads the team says "few people have been able to study the birth place of planets by observing polarized light with a large telescope. Our results show that this is a very rewarding approach. We plan on extending our research to other disks, to get a comprehensive picture of how dust transforms into planets." * ESA's ISO provides the first view of monstrous stars being born ----------------------------------------------------------------- (ESA Press Release, April 20th, 2006) (http://www.esa.int/esaCP/SEM8MZNFGLE_index_0.html) Scientists have secured their first look at the birth of monstrous stars that shine 100 000 times more brightly than the Sun, thanks to ESA's Infrared Space Observatory (ISO). The discovery allows astronomers to begin investigating why only some regions of space promote the growth of these massive stars. Space is littered with giant clouds of gas. Occasionally, regions within these clouds collapse to form stars. "One of the major questions in the field of study is why do some clouds produce high- and low-mass stars, whilst others form only low-mass stars?" asks Oliver Krause, Max-Planck-Institut für Astronomie, Heidelberg and Steward Observatory, Arizona. The conditions necessary to form high-mass stars are difficult to deduce because such stellar monsters form far away and are shrouded behind curtains of dust. Only long wavelengths of infrared radiation can escape from these obscuring cocoons and reveal the low temperature dust cores that mark the sites of star formation. This radiation is exactly what ISO's ISOPHOT far-infrared camera has collected. Stephan Birkmann, Oliver Krause and Dietrich Lemke, all of the Max-Planck-Institut für Astronomie, Heidelberg, used ISOPHOT's data to zero-in on two intensely cold and dense cores, each containing enough matter to form at least one massive star. "This opens up a new era for the observations of the early details of high-mass star formation," says Krause. study pioneered by Lemke. He realised that when ISO was turning from one celestial object to another, valuable observing time was being lost. He organised for ISOPHOT's far-infrared camera to continuously record during such slews and beam this data to Earth. During the ISO mission, which lasted for two and a half years during 199598, the spacecraft made around 10 000 slews, providing a web of data across the sky for the previously unexplored window of infrared emission at 170 micrometres. This wavelength is 310 times longer than optical radiation and reveals cold dust down to just 10K (263 degrees Celsius). A catalogue was produced of the cold sites in the survey. Birkmann and his colleagues investigated this catalogue and found fifty potential places of high-mass stellar birth. A campaign of follow-up observations using ground-based telescopes revealed that object ISOSS J18364-0221 was in fact two cold dense cores that looked suspiciously like those associated with the birth of low-mass stars, but containing much more mass. The first core is at 16.5 Kelvin (256.5 degrees Celsius). It contains seventy-five times the mass of the Sun and shows signs of gravitational collapse. The second one is around 12K (261 degrees Celsius) and contains 280 solar masses. The team are currently studying the other potential sites. * Cosmic Spider is Good Mother ------------------------------ (ESO Press Release, April 7th, 2006) (http://eso.org/outreach/press-rel/pr-2006/pr-13-06.html) Hanging above the Large Magellanic Cloud (LMC) - one of our closest galaxies - in what some describe as a frightening sight, the Tarantula nebula is worth looking at in detail. Also designated 30 Doradus or NGC 2070, the nebula owes its name to the arrangement of its brightest patches of nebulosity that somewhat resemble the legs of a spider. This name, of the biggest spiders on Earth, is also very fitting in view of the gigantic proportions of the celestial nebula - it measures nearly 1,000 light years across! The Tarantula nebula is the largest emission nebula in the sky and also one of the largest known star-forming regions in all the Milky Way's neighbouring galaxies. Located about 170,000 light-years away, in the southern constellation Dorado (The Swordfish), it can be seen with the unaided eye. As shown in this image obtained with the FORS1 multi-mode instrument on ESO's Very Large Telescope, its structure is fascinatingly complex, with a large number of bright arcs and apparently dark areas in between. Inside the giant emission nebula lies a cluster of young, massive and hot stars, denoted R 136, whose intense radiation and strong winds make the nebula glow, shaping it into the form of a giant arachnid. The cluster is about 2 to 3 million years old, that is, almost from 'yesterday' in the 13.7 billion year history of the Universe. Several of the brighter members in the immediate surroundings of the dense cluster are among the most massive stars known, with masses well above 50 times the mass of our Sun. The cluster itself contains more than 200 massive stars. In the upper right of the image, another cluster of bright, massive stars is seen. Known to astronomers as Hodge 301, it is about 20 million years old, or about 10 times older than R136. The more massive stars of Hodge 301 have therefore already exploded as supernovae, blasting material away at tremendous speed and creating a web of entangled filaments. More explosions will come soon - in astronomical terms - as three red supergiants are indeed present in Hodge 301 that will end their life in the gigantic firework of a supernova within the next million years. While some stars are dying in this spidery cosmic inferno, others are yet to be born. Some structures, seen in the lower part of the image, have the appearance of elephant trunks, not unlike the famous and fertile "Pillars of Creation" at the top of which stars are forming. In fact, it seems that stars form all over the place in this gigantic stellar nursery and in all possible masses, at least down to the mass of our Sun. In some places, in a marvellous recycling process, it is the extreme radiation from the hot and massive stars and the shocks created by the supernova explosions that has compressed the gas to such extent to allow stars to form. To the right and slightly below the central cluster, a red bubble is visible. The star that blows the material making this bubble is thought to be 20 times more massive, 130 000 times more luminous, 10 times larger and 6 times hotter than our Sun. A possible fainter example of such a bubble is also visible just above the large red bubble in the image. Earlier colour composite images of the Tarantula nebula have been made with other instruments and/or filters at ESO's telescopes, e.g. PR Photo 05a/00 in visual light with FORS2 at the VLT at Paranal, and PR Photos 14a-g/02 and 34a-h/04 with the Wide-Field Imager at the ESO/MPG 2.2-m telescope at La Silla. * Upgraded MERLIN Spies Cloud of Alcohol Spanning 288 Billion Miles ------------------------------------------------------------------- (RAS Press Release, April 4th, 2006) (http://www.ras.org.uk/index.php?option=com_content&task=view&id=973&Itemid=2) Astronomers based at Jodrell Bank Observatory have discovered a giant bridge of methyl alcohol, spanning approximately 288 billion miles, wrapped around a stellar nursery. The gas cloud could help our understanding of how the most massive stars in our galaxy are formed. The new observations were taken with the UK's MERLIN radio telescopes, which have recently been upgraded. The team studied an area called W3(OH), a region in our galaxy where stars are being formed by the gravitational collapse of a cloud of gas and dust. The observations have revealed giant filaments of gas that are emitting as `masers' (molecules in the gas are amplifying and emitting beams of microwave radiation in much the same way as a laser emits beams of light). The filaments of masing gas form giant bridges between maser `spots' in W3(OH) that had been observed previously. The largest of these maser filaments is 288 billion miles (463 billion km) long. Observations show that the entire gas cloud appears to be rotating as a disc around a central star, in a similar manner to the accretion discs in which planets form around young stars. The maser filaments occur at shock boundaries where large regions of gas are colliding. "Our discovery is very interesting because it challenges some long-accepted views held in astronomical maser research. Until we found these filaments, we thought of masers as point-like objects or very small bright hotspots surrounded by halos of fainter emission," said Dr Lisa Harvey-Smith, who is the Principal Investigator for the study and is presenting results at the Royal Astronomical Society's National Astronomy Meeting on 4th April. Since the upgrade of the UK's MERLIN telescope network, astronomers have been able to image methanol masers with a much higher sensitivity and, for the first time, get a complete picture of all the radiation surrounding maser sources. In the new study, the Jodrell Bank team looked at the motion of the W3(OH) star forming region in 3-dimensions and also measured physical properties of the gas such as temperature, pressure and the strength and direction of the magnetic fields. This information is vital when testing theories about how stars are born from the primordial gas in stellar nurseries. Dr Harvey-Smith said, "There are still many unanswered questions about the birth of massive stars because the formation centres are shrouded by dust. The only radiation that can escape is at radio wavelengths and the upgraded MERLIN network is now giving us the first opportunity to look deep into these star forming regions and see what's really going on." The many different types of interactions between molecules in star forming regions lead to emissions in many different wavelengths. Future observations of masers at other frequencies are planned to complete the complex jigsaw puzzle that has now been revealed. Dr Harvey-Smith adds, "Although it is exciting to discover a cloud of alcohol almost 300 billion miles across, unfortunately methanol, unlike its chemical cousin ethanol, is not suitable for human consumption!" * Eta Carinae: A Spectacular Show From A Convulsing Massive Star ---------------------------------------------------------------- (Gemini Observatory Press Release, April 12th, 2006) (http://www.gemini.edu/index.php?option=content&task=view&id=180) Although the Homunculus Nebula around the massive star Eta Carinae has been the subject of intense study for many years, it has always been reluctant to divulge its innermost secrets. However, an important chapter in the recent evolution of this unique star was revealed when Nathan Smith (University of Colorado) used the high-resolution infrared spectrograph PHOENIX on the Gemini South telescope to observe the bipolar nebula surrounding Eta Carinae. Multi-slit spectroscopy allowed Smith to reconstruct both the geometry and the velocity structure of the expanding gas in the nebula based on the behavior of the molecular line of hydrogen H2 at 2.1218 microns and the atomic line of ionized iron [Fe II] at 1.6435 microns. Analysis of the PHOENIX spectrum shows a very well-defined shell structure expanding ballistically at about 500 kilometers per second. A "thick," warm inner dust shell traced by [Fe II] emission is surrounded by a cooler and denser outer shell that is traced by strong H2 emission. Even though the outer H2 skin is remarkably thin and uniform it contains about 11 solar masses of gas and dust ejected over a period of less than five years. The Gemini spectra show that the density in the outer shell may reach 107 particles per cm3. The spatio-kinematic structure of H2 emission at the pinched waist of the nebula helps explain the unusual and complex structures seen in other high-resolution images. The current shape of the Homunculus nebula is of two well-defined polar lobes outlined by an outer massive shell of gas and dust. Smith states that these Gemini/PHOENIX data indicate that most of the mass lost during the Great Eruption of the mid-nineteenth century was limited to the high latitudes of the star, with almost all of the mechanical energy escaping between 45 degrees and the pole. "The mass distribution in the nebula indicates that its shape is a direct result of an aspherical explosion from the star itself, instead of being pinched at the waist by the surrounding circumstellar material," said Smith. * Exploding 'Star Within A Star' -------------------------------- (RAS Press Release, April 7th, 2006) (http://www.ras.org.uk/index.php?option=com_content&task=view&id=987&Itemid=2) On 12 February 2006, amateur astronomers reported that a faint star in the constellation of Ophiuchus had suddenly become clearly visible in the night sky without the aid of a telescope. Records show that this so-called recurrent nova, RS Ophiuchi (RS Oph), has previously reached this level of brightness five times in the last 108 years, most recently in 1985. The latest explosion has been observed in unprecedented detail by an armada of space- and ground-based telescopes. Speaking today (Friday) at the RAS National Astronomy Meeting at Leicester, Professor Mike Bode of Liverpool John Moores University and Dr Tim O'Brien of Jodrell Bank Observatory will present the latest results which are shedding new light on what happens when stars explode. RS Oph is just over 5,000 light years away from Earth. It consists of a white dwarf star (the super-dense core of a star, about the size of the Earth, that has reached the end of its main hydrogen-burning phase of evolution and shed its outer layers) in close orbit with a much larger red giant star. The two stars are so close together that hydrogen-rich gas from the outer layers of the red giant is continuously pulled onto the dwarf by its high gravity. After around 20 years, enough gas has been accreted that a runaway thermonuclear explosion occurs on the white dwarf's surface. In less than a day, its energy output increases to over 100,000 times that of the Sun, and the accreted gas (several times the mass of the Earth) is ejected into space at speeds of several thousand km per second. Five explosions such as this per century can only be explained if the white dwarf is near the maximum mass it could have without collapsing to become an even denser neutron star. What is also very unusual in RS Oph is that the red giant is losing enormous amounts of gas in a wind that envelops the whole system. As a result, the explosion on the white dwarf occurs "inside" its companion's extended atmosphere and the ejected gas then slams into it at very high speed. Within hours of notification of the latest outburst of RS Oph being relayed to the international astronomical community, telescopes both on the ground and in space swung into action. Among these is NASA's Swift satellite which, as its name suggests, can be used to react rapidly to things that change in the sky. Included in its armoury of instruments is an X-ray Telescope (XRT), designed and built by the University of Leicester. "We realised from the few X-ray measurements taken late in the 1985 outburst that this was an important part of the spectrum in which to observe RS Oph as soon as possible," said Professor Mike Bode of Liverpool John Moores University, who led the observing campaign for the 1985 outburst and now heads the Swift follow-up team on the current explosion. "The expectation was that shocks would be set up both in the ejected material and in the red giant's wind, with temperatures initially of up to around 100 million degrees Celsius - nearly 10 times that in the core of the Sun. We have not been disappointed! " The first observations by Swift, only three days after the outburst began, revealed a very bright X-ray source. Over the initial few weeks, it became even brighter and then began to fade, with the spectrum suggesting that the gas was cooling down, although still at a temperature of tens of millions of degrees. This was exactly what was expected as the shock pushed into the red giant's wind and slowed down. Then something remarkable and unexpected happened to the X-ray emission. "About a month after the outburst, the X-ray brightness of RS Oph increased very dramatically," explained Dr. Julian Osborne of the University of Leicester. "This was presumably because the hot white dwarf, which is still burning nuclear fuel, then became visible through the red giant's wind. "This new X-ray flux was extremely variable, and we were able to see pulsations which repeat every 35 seconds or so. Although it is very early days, and data are still being taken, one possibility for the variability is that this is due to instability in the nuclear burning rate on the white dwarf." Observatories Swing Into Action Meanwhile, observatories working at other wavelengths changed their programmes to observe the event. Dr. Tim O'Brien of Jodrell Bank Observatory, who did his PhD thesis work on the 1985 explosion, and Dr. Stewart Eyres of the University of Central Lancashire, lead the team that is securing the most detailed radio observations to date of such an event. "In 1985, we were not able to begin observing RS Oph until nearly three weeks after the outburst, and then with facilities that were far less capable than those available to us today," said Dr. O'Brien. "Both the radio and X-ray observations from the last outburst gave us tantalising glimpses of what was happening as the outburst evolved. In addition, this time, we have developed very much more advanced computer models. The combination of the two now will undoubtedly lead to a greater understanding of the circumstances and consequences of the explosion. "In 2006, our first observations with the UK's MERLIN system were made only four days after the outburst and showed the radio emission to be much brighter than expected," added Dr. Eyres. "Since then it has brightened, faded, then brightened again. With radio telescopes in Europe, North America and Asia now monitoring the event very closely, this is our best chance yet of understanding what is truly going on." Optical observations are also being obtained by many observatories around the globe, including the robotic Liverpool Telescope on La Palma. Observations are also being conducted at the longer wavelengths of the infrared part of the spectrum. "For the first time we are able to see the effects of the explosion and its aftermath at infrared wavelengths from space, with NASA's Spitzer Space Telescope," said Professor Nye Evans of Keele University, who heads the infrared follow-up team. "Meanwhile, the observations we have already obtained from the ground, from the United Kingdom Infrared Telescope on the summit of Mauna Kea in Hawai'i, already far surpass the data we had during the 1985 eruption. "The shocked red giant wind and the material ejected in the explosion give rise to emission not only at X-ray, optical and radio wavelengths, but also in the infrared, via coronal lines (so-called because they are prominent in the Sun's very hot corona). These will be crucial in determining the abundances of the elements in the material ejected in the explosion and in confirming the temperature of the hot gas." 26 February 2006 was a highlight of the observational campaign. In what must surely be a unique event, four space satellites, plus radio observatories around the globe, observed RS Oph on the same day. "This star could not have exploded at a better time for international ground and space based studies of an event which has been changing every time we look at it," said Professor Sumner Starrfield of Arizona State University, who heads the U.S. side of the collaboration. "We are all very excited and exchanging many emails every day trying to understand what is happening on that day and then predict the behaviour on the next." What is apparent is that RS Oph is behaving like a "Type II" supernova remnant. Type II supernovae represent the catastrophic death of a star at least 8 times the mass of the Sun. They also eject very high velocity material which interacts with their surroundings. However, the full evolution of a supernova remnant takes tens of thousands of years. In RS Oph, this evolution is literally occurring before our eyes, around 100,000 times faster. "In the 2006 outburst of RS Oph, we have a unique opportunity of understanding much more fully such things as runaway thermonuclear explosions and the end-points of the evolution of stars," said Professor Bode. "With the observational tools now at our disposal, our efforts 21 years ago look rather primitive by comparison." * XMM-Newton reveals a tumbling neutron star -------------------------------------------- (ESA Press Release, April 19th, 2006) (http://www.esa.int/esaCP/SEMSIWNFGLE_index_0.html) Using data from ESA's XMM-Newton X-ray observatory, an international group of astrophysicists discovered that one spinning neutron star doesn't appear to be the stable rotator scientists would expect. These X-ray observations promise to give new insights into the thermal evolution and finally the interior structure of neutron stars. Spinning neutron stars, also known as pulsars, are generally known to be highly stable rotators. Thanks to their periodic signals, emitted either in the radio or in the X-ray wavelength, they can serve as very accurate astronomical 'clocks'. The scientists found that over the past four and a half years the temperature of one enigmatic object, named RX J0720.4-3125, kept rising. However, very recent observations have shown that this trend reversed and the temperature is now decreasing. According to the scientists this effect is not due to a real variation in temperature, but instead to a changing viewing geometry. RX J0720.4-3125 is most probably 'precessing', that is it is slowly tumbling and therefore, over time, it exposes to the observers different areas of the surface. Neutron stars are one of the endpoints of stellar evolution. With a mass comparable to that of our Sun confined into a sphere of 20-40 km diameter, their density is even somewhat higher than that of an atomic nucleus - a billion tonnes per cubic centimetre. Soon after their birth in a supernova explosion their temperature is of the order of 1 000 000 ºC and the bulk of their thermal emission falls in the X-ray band of the electromagnetic spectrum. Young isolated neutron stars are slowly cooling down and it takes a million years before they become too cold to be observable in X-rays. Neutron stars are known to possess very strong magnetic fields, typically several trillion times stronger than that of the Earth. The magnetic field can be so strong that it influences the heat transport from the stellar interior through the crust leading to hot spots around the magnetic poles on the star surface. It is the emission from these hotter polar caps which dominates the X-ray spectrum. There are only a few isolated neutron stars known from which we can directly observe the thermal emission from the surface of the star. One of them is RX J0720.4-3125, rotating with a period of about eight and a half seconds. "Given the long cooling time scale it was therefore highly unexpected to see its X-ray spectrum changing over a couple of years," said Frank Haberl from the Max-Planck-Institute for Extraterrestrial Physics in Garching (Germany), who led the research group. "It is very unlikely that the global temperature of the neutron star changes that quickly. We are rather seeing different areas of the stellar surface at different times. This is also observed during the rotation period of the neutron star when the hot spots are moving in and out of our line of sight, and so their contribution to the total emission changes," Haberl continued. A similar effect on a much longer time scale can be observed when the neutron star precesses (similarly to a spinning top). In that case the rotation axis itself moves around a cone leading to a slow change of the viewing geometry over the years. Free precession can be caused by a slight deformation of the star from a perfect sphere, which may have its origin in the very strong magnetic field. During the first XMM-Newton observation of RX J0720.4-3125 in May 2000, the observed temperature was at minimum and the cooler, larger spot was predominantly visible. On the other hand, four years later (May 2004) the precession brought into view mostly the second, hotter and smaller spot, that made the observed temperature increase. This likely explains the observed variation in temperature and emitting areas, and their anti-correlation. In their work Haberl and colleagues developed a model for RX J0720.4-3125 which can explain many of the peculiar characteristics which have been a challenge to explain so far. In this model the long-term change in temperature is produced by the different fractions of the two hot polar caps which enter into view as the star precesses with a period of about seven to eight years. In order for such a model to work, the two emitting polar regions need to have different temperatures and sizes, as it has been recently proposed in the case of another member of the same class of isolated neutron stars. According to the team, RX J0720.4-3125 is probably the best case to study precession of a neutron star via its X-ray emission directly visible from the stellar surface. Precession may be a powerful tool to probe the neutron star interior and learn about the state of matter under conditions which we can not produce in the laboratory. Additional XMM-Newton observations are planned to further monitor this intriguing object. "We are continuing the theoretical modelling from which we hope to learn more about the thermal evolution, the magnetic field geometry of this particular star and the interior structure of neutron stars in general," Haberl concluded. * NASA's Spitzer Finds Hints of Planet Birth Around Dead Star ------------------------------------------------------------- (NASA News, April 5th, 2006) (http://www.jpl.nasa.gov/news/news.cfm?release=2006-049) NASA's Spitzer Space Telescope has uncovered new evidence that planets might rise up out of a dead star's ashes. The infrared telescope surveyed the scene around a pulsar, the remnant of an exploded star, and found a surrounding disk made up of debris shot out during the star's death throes. The dusty rubble in this disk might ultimately stick together to form planets. This is the first time scientists have detected planet-building materials around a star that died in a fiery blast. "We're amazed that the planet-formation process seems to be so universal," said Dr. Deepto Chakrabarty of the Massachusetts Institute of Technology in Cambridge, principal investigator of the new research. "Pulsars emit a tremendous amount of high energy radiation, yet within this harsh environment we have a disk that looks a lot like those around young stars where planets are formed." A paper on the Spitzer finding appears in the April 6 issue of Nature. Other authors of the paper are lead author Zhongxiang Wang and co-author David Kaplan, both of the Massachusetts Institute of Technology. The finding also represents the missing piece in a puzzle that arose in 1992, when Dr. Aleksander Wolszczan of Pennsylvania State University found three planets circling a pulsar called PSR B1257+12. Those pulsar planets, two the size of Earth, were the first planets of any type ever discovered outside our solar system. Astronomers have since found indirect evidence the pulsar planets were born out of a dusty debris disk, but nobody had directly detected this kind of disk until now. The pulsar observed by Spitzer, named 4U 0142+61, is 13,000 light-years away in the Cassiopeia constellation. It was once a large, bright star with a mass between 10 and 20 times that of our sun. The star probably survived for about 10 million years, until it collapsed under its own weight about 100,000 years ago and blasted apart in a supernova explosion. Some of the debris, or "fallback," from that explosion eventually settled into a disk orbiting the shrunken remains of the star, or pulsar. Spitzer was able to spot the warm glow of the dusty disk with its heat-seeking infrared eyes. The disk orbits at a distance of about 1 million miles and probably contains about 10 Earth-masses of material. Pulsars are a class of supernova remnants, called neutron stars, which are incredibly dense. They have masses about 1.4 times that of the sun squeezed into bodies only 10 miles wide. One teaspoon of a neutron star would weigh about 2 billion tons. Pulsar 4U 0142+61 is an X-ray pulsar, meaning that it spins and pulses with X-ray radiation. Any planets around the stars that gave rise to pulsars would have been incinerated when the stars blew up. The pulsar disk discovered by Spitzer might represent the first step in the formation of a new, more exotic type of planetary system, similar to the one found by Wolszczan in 1992. "I find it very exciting to see direct evidence that the debris around a pulsar is capable of forming itself into a disk. This might be the beginning of a second generation of planets," Wolszczan said. Pulsar planets would be bathed in intense radiation and would be quite different from those in our solar system. "These planets must be among the least hospitable places in the galaxy for the formation of life," said Dr. Charles Beichman, an astronomer at NASA's Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, Calif. * NASA Achieves Breakthrough in Black Hole Simulation ----------------------------------------------------- (NASA News, April 18th, 2006) (http://www.nasa.gov/home/hqnews/2006/apr/HQ_06188_black_hole_simulation.html) NASA scientists have reached a breakthrough in computer modeling that allows them to simulate what gravitational waves from merging black holes look like. The three-dimensional simulations, the largest astrophysical calculations ever performed on a NASA supercomputer, provide the foundation to explore the universe in an entirely new way. According to Einstein's math, when two massive black holes merge, all of space jiggles like a bowl of Jell-O as gravitational waves race out from the collision at light speed. Previous simulations had been plagued by computer crashes. The necessary equations, based on Einstein's theory of general relativity, were far too complex. But scientists at NASA's Goddard Space Flight Center in Greenbelt, Md., have found a method to translate Einstein's math in a way that computers can understand. "These mergers are by far the most powerful events occurring in the universe, with each one generating more energy than all of the stars in the universe combined. Now we have realistic simulations to guide gravitational wave detectors coming online," said Joan Centrella, head of the Gravitational Astrophysics Laboratory at Goddard. The simulations were performed on the Columbia supercomputer at NASA's Ames Research Center near Mountain View, Calif. This work appears in the March 26 issue of Physical Review Letters and will appear in an upcoming issue of Physical Review D. The lead author is John Baker of Goddard. Similar to ripples on a pond, gravitational waves are ripples in space and time, a four-dimensional concept that Einstein called spacetime. They haven't yet been directly detected. Gravitational waves hardly interact with matter and thus can penetrate the dust and gas that blocks our view of black holes and other objects. They offer a new window to explore the universe and provide a precise test for Einstein's theory of general relativity. The National Science Foundation's ground-based Laser Interferometer Gravitational-Wave Observatory and the proposed Laser Interferometer Space Antenna, a joint NASA - European Space Agency project, hope to detect these subtle waves, which would alter the shape of a human from head to toe by far less than the width of an atom. Black hole mergers produce copious gravitational waves, sometimes for years, as the black holes approach each other and collide. Black holes are regions where gravity is so extreme that nothing, not even light, can escape their pull. They alter spacetime. Therein lies the difficulty in creating black hole models: space and time shift, density becomes infinite and time can come to a standstill. Such variables cause computer simulations to crash. These massive, colliding objects produce gravitational waves of differing wavelengths and strengths, depending on the masses involved. The Goddard team has perfected the simulation of merging, equal-mass, non-spinning black holes starting at various positions corresponding to the last two to five orbits before their merger. With each simulation run, regardless of the starting point, the black holes orbited stably and produced identical waveforms during the collision and its aftermath. This unprecedented combination of stability and reproducibility assured the scientists that the simulations were true to Einstein's equations. The team has since moved on to simulating mergers of non-equal-mass black holes. Einstein's theory of general relativity employs a type of mathematics called tensor calculus, which cannot easily be turned into computer instructions. The equations need to be translated, which greatly expands them. The simplest tensor calculus equations require thousands of lines of computer code. The expansions, called formulations, can be written in many ways. Through mathematical intuition, the Goddard team found the appropriate formulations that led to suitable simulations. * Deadly astronomical event not likely to happen in our galaxy, study finds ---------------------------------------------------------------------------- (Ohio State News, April 20th, 2006) (http://researchnews.osu.edu/archive/gammaray.htm) Are you losing sleep at night because you're afraid that all life on Earth will suddenly be annihilated by a massive dose of gamma radiation from the cosmos? Well, now you can rest easy. Some scientists have wondered whether a deadly astronomical event called a gamma ray burst could happen in a galaxy like ours, but a group of astronomers at Ohio State University and their colleagues have determined that such an event would be nearly impossible. Gamma ray bursts (GRBs) are high-energy beams of radiation that shoot out from the north and south magnetic poles of a particular kind of star during a supernova explosion, explained Krzysztof Stanek, associate professor of astronomy at Ohio State. Scientists suspect that if a GRB were to occur near our solar system, and one of the beams were to hit Earth, it could cause mass extinctions all over the planet. The GRB would have to be less than 3,000 light years away to pose a danger, Stanek said. One light year is approximately 6 trillion miles, and our galaxy measures 100,000 light years across. So the event would not only have to occur in our galaxy, but relatively close by, as well. In the new study, which Stanek and his coauthors submitted to the Astrophysical Journal, they found that GRBs tend to occur in small, misshapen galaxies that lack heavy chemical elements (astronomers often refer to all elements other than the very lightest ones -- hydrogen, helium, and lithium -- as metals). Even among metal-poor galaxies, the events are rare -- astronomers only detect a GRB once every few years. But the Milky Way is different from these GRB galaxies on all counts -- it's a large spiral galaxy with lots of heavy elements. The astronomers did a statistical analysis of four GRBs that happened in nearby galaxies, explained Oleg Gnedin, a postdoctoral researcher at Ohio State. They compared the mass of the four host galaxies, the rate at which new stars were forming in them, and their metal content to other galaxies catalogued in the Sloan Digital Sky Survey. Though four may sound like a small sample compared to the number of galaxies in the universe, these four were the best choice for the study because astronomers had data on their composition, Stanek said. All four were small galaxies with high rates of star formation and low metal content. Of the four galaxies, the one with the most metals -- the one most similar to ours -- hosted the weakest GRB. The astronomers determined that the odds of a GRB occurring in a galaxy like that one to be approximately 0.15 percent. And the Milky Way's metal content is twice as high as that galaxy, so our odds of ever having a GRB would be even lower than 0.15 percent. "We didn't bother to compute the odds for our galaxy, because 0.15 percent seemed low enough," Stanek said. He figures that most people weren't losing sleep over the possibility of an Earth-annihilating GRB. "I wouldn't expect the stock market to go up as a result of this news, either," he said. "But there are a lot of people who have wondered whether GRBs could be blamed for mass extinctions early in Earth's history, and our work suggests that this is not the case." Astronomers have studied GRBs for more than 40 years, and only recently determined where they come from. In fact, Stanek led the team that tied GRBs to supernovae in 2003. He and Gnedin explained that when a very massive, rapidly rotating star explodes in a supernova, its magnetic field directs gamma radiation to flow only out of the star's north and south magnetic poles, forming high-intensity jets. Scientists have measured the energies of these events and assumed -- rightly so, Stanek said -- that such high-intensity radiation could destroy life on a planet. That's why some scientists have proposed that a GRB could have been responsible for a mass extinction that occurred on Earth 450 million years ago. Now it seems that gamma ray bursts may not pose as much a danger to Earth or any other potential life in the universe, either, since they are unlikely to occur where life would develop. Planets need metals to form, Stanek said, so a low-metal galaxy would probably have fewer planets, and fewer chances for life. He added that he didn't originally intend to address the question of mass extinctions. The study grew out of a group discussion during the Ohio State Department of Astronomy's "morning coffee" -- a daily half-hour where faculty and students review new astronomy journal articles that have been posted to Internet preprint servers overnight. In February, Stanek published a paper on a GRB he had observed, and during coffee someone asked whether he thought it was just a coincidence that these events seem to happen in small, metal-poor galaxies. "My initial reaction was that it's not a coincidence, and everyone just knows that GRBs happen in metal-poor galaxies. But then people asked, 'Is it really that well known? Has anybody actually proven it to be true?' And we realized that nobody had." As a result, the list of coauthors on the paper includes astronomers across a broad range of expertise, which Stanek said is somewhat unusual in these days of specialized research. The coauthors were among faculty gathered for coffee that day, plus a few friends they recruited to help them: Stanek and Gnedin; John Beacom, assistant professor of physics and astronomy; Jennifer Johnson, assistant professor of astronomy; Juna Kollmeier, a graduate student; Andrew Gould, Marc Pinsonneault, Richard Pogge, and David Weinberg, all professors of astronomy at Ohio State; and Maryam Modjaz, a graduate student at the Harvard-Smithsonian Center for Astrophysics. * Unravelling a cosmic mystery - Scientists discover the Universe's strongest magnetic field ------------------------------------------------------------------------------------------- (University of Exeter Press Release, April 3rd, 2006) (http://www.exeter.ac.uk/news/magnetic.shtml) Scientists from The University of Exeter and the International University, Bremen have discovered what is thought to be the strongest magnetic field in the Universe. In a paper in the journal Science, Dr Daniel Price and Professor Stephan Rosswog show that violent collisions between neutron stars in the outer reaches of space create this field, which is 1000 million million times larger than our earth's own magnetic field. It's thought that these collisions could be behind some of the brightest explosions in the Universe since the Big Bang, so-called short Gamma-ray bursts. Dr Daniel Price, of the School of Physics at The University of Exeter, said: " We have managed to simulate, for the first time, what happens to the magnetic field when neutron stars collide, and it seems possible that the magnetic field produced could be sufficient to spark the creation of Gamma-ray bursts. Gamma-ray bursts are the most powerful explosions we can detect but until recently little to nothing has been known about how they are generated. It's thought that strong magnetic fields are essential in producing them, but until now no one has shown how fields of the required intensity could be created." He continues: "What really surprised us was just how fast these tremendous fields are generated - within one or two milliseconds after the stars hit each other." Prof Stephan Rosswog, of the International University, Bremen, Germany, adds: "Even more incredible is that the magnetic field strengths reached in the simulations are just lower limits on the strengths that may be actually be produced in nature. It has taken us months of nearly day and night programming to get this project running - just to calculate a few milliseconds of a single collision takes several weeks on a supercomputer." The remnants of supernovae, neutron stars are formed when massive stars run out of nuclear fuel and explode, shedding their outer layers and leaving behind a small but extremely dense core. When two neutron stars are left orbiting each other, they will spiral slowly together, resulting in these massive collisions. * Hubble's view of Cigar Galaxy on sixteenth mission anniversary ---------------------------------------------------------------- (ESA Press Release, April 24th, 2006) (http://www.esa.int/esaCP/SEMEQ8OFGLE_index_0.html) To celebrate the NASA-ESA Hubble Space Telescope's 16 years of success, the two space agencies are releasing the sharpest wide-angle view ever obtained of Messier 82 (M82), a galaxy remarkable for its webs of shredded clouds and flame-like plumes of glowing hydrogen blasting out from its central regions. Located 12 million light-years away, M82 appears high in the northern spring sky in the direction of the constellation Ursa Major, the Great Bear. It is also called the 'Cigar Galaxy' because of the elongated elliptical shape produced by the tilt of its starry disk relative to our line of sight. As shown in this mosaic image, M82 is a magnificent starburst galaxy. Throughout its central region young stars are being born ten times faster than they are inside in our Milky Way Galaxy. These numerous hot new stars not only emit radiation but also charged particles that form the so-called stellar wind. Stellar winds streaming from these stars combine to form a galactic 'superwind'. The superwind compresses enough gas to trigger the ignition of millions more stars and blasts out towering plumes of hot ionised hydrogen gas, above and below the disk of the galaxy (seen in red in the image). In M82 young stars are crammed into star clusters. These then congregate by the dozen to make the bright patches or 'starburst clumps' seen in the central parts of M82. The individual clusters in the clumps can only be distinguished in the ultra-sharp Hubble images. Most of the pale objects sprinkled around the main body of M82 that look like fuzzy stars are actually star clusters about 20 light-years across and containing up to a million stars. The rapid rate of star formation in this galaxy will eventually be self-limiting. When star formation becomes too vigorous, it destroys the material needed to make more stars. So the starburst will eventually subside, probably in a few tens of millions of years. The observation was made in March 2006 with the Advanced Camera for Surveys' Wide Field Channel. Astronomers assembled the six-image composite mosaic by combining exposures taken with four coloured filters. These capture starlight from visible and infrared wavelengths as well as the light from the glowing hydrogen filaments. * The universe trapped in its own web ------------------------------------- (RAS Press Release, April 4th, 2006) (http://www.ras.org.uk/index.php?option=com_content&task=view&id=972&Itemid=2) Astronomers from the University of Nottingham, UK, and the Instituto de Astrofisica de Canarias (Spain), have found the first observational evidence that galaxies are not randomly oriented. Instead, they are aligned following a characteristic pattern dictated by the large-scale structure of the invisible dark matter that surrounds them. This discovery confirms one of the fundamental aspects of galaxy formation theory and implies a direct link between the global properties of the Universe and the individual properties of galaxies. Galaxy formation theories predicted such an effect, but its empirical verification has remained elusive until now. The results of this work were published the 1 April issue of Astrophysical Journal Letters. Nowadays, matter is not distributed uniformly throughout space but is instead arranged in an intricate "cosmic web" of filaments and walls surrounding bubble-like voids. Regions with high galaxy concentrations are known as galaxy clusters whereas low density regions are termed voids. This inhomogeneous distribution of matter is called the "Large-scale distribution of the Universe." When the Universe is considered as whole, this distribution has a similar appearance to a spider's web or the neural network of the brain. But it was not always like this. After the Big Bang, when the Universe was much younger, matter was distributed homogeneously. As the Universe was evolving, gravitational pulls began to compress the matter in certain regions of space, forming the large-scale structure that we currently observe. According to these models and theories a direct consequence of this process is that galaxies should be preferentially oriented perpendicularly to the direction of the linear filaments. Several observational studies have looked for a preferential spatial orientation (or alignment) of galaxy rotation axes with respect to their surrounding large-scale structures. However, none of them have been successful, due to the difficulties associated with trying to characterise the filaments. The research conducted by the astrophysical group formed by Ignacio Trujillo (University of Nottingham, UK), Conrado Carretero and Santiago G. Patiri, (both from the Instituto de Astrofisica de Canarias, Spain) has been able to measure this effect, confirming theoretical predictions. To achieve this goal, they used a new technique based on the analysis of the huge voids that are found in the large-scale structure of the Universe. These voids have been detected by searching for large regions of space depleted of bright galaxies. In addition, they took advantage of information provided by the two largest sky surveys yet undertaken: the Sloan Digital Sky Survey and the Two Degree Field Survey. These surveys contain positional information for more than half a million galaxies located within a distance of one billion light-years of the Earth. Other parameters provided by the surveys, such as the position angle and the ellipticity of the objects, were used to estimate the orientation of the disk galaxies. "We found that there is an excess of disk galaxies that are highly inclined relative to the plane defined by the large-scale structure surrounding them," explained Dr. Trujillo. "Their rotation axes are mainly oriented in the direction of the filaments. "Our work provides important confirmation of the tidal torque theory which explains how galaxies have acquired their current spin," said Trujillo. "The spin of the galaxies is believed to be intrinsically linked to their morphological shapes. So, this work is a step forward on our understanding of how galaxies have reached their current shapes." * The Search For The History Of The Universe's Light Emission ------------------------------------------------------------- (PPARC Press Release, April 20th, 2006) (http://www.pparc.ac.uk/Nw/GammaRay.asp) The light emitted from all objects in the Universe during its entire history - stars, galaxies, quasars etc. forms a diffuse sea of photons that permeates intergalactic space, referred to as "diffuse extragalactic background light" (EBL). Scientists have long tried to measure this fossil record of the luminous activity in the Universe in their quest to decipher the history and evolution of the Cosmos, but its direct determination from the diffuse glow of the night sky is very difficult and uncertain. Very high energy (VHE) gamma-rays, some 100,000,000,000 times more energetic than normal light, offer an alternative way to probe this background light, and UK researchers from Durham University in collaboration with international partners used the High Energy Stereoscopic System (HESS) gamma-ray telescopes in the Khomas Highlands of Namibia to observe several quasars (the most luminous VHE gamma-ray sources known) with this goal in mind. The results, to be published in the April 20 issue of Nature, turned out to be rather striking. Gamma-rays, which are produced in the most violent objects in the Universe, are absorbed in their journey from distant objects to Earth if they happen to hit a photon of "normal" background light. This fog of light in which the Universe is bathed is a fossil record of all the light emitted in the Universe over its lifetime, from the glare of the first stars and galaxies up to the present time. So, using the distant quasars as a probe and studying the effect of the fossil light on the energy distribution of the initial gamma-rays, astrophysicists used HESS to derive a limit on the maximum amount of this 'extragalactic background light', which is remarkably lower than what previous estimates had suggested. This result, published in the April 20 issue of Nature, has important consequences for our understanding of galaxy formation and evolution, and expands the horizon of the gamma-ray Universe which is clearly more transparent to gamma-rays than previously believed Commenting in the findings, Dr Lowry McComb of Durham University, said, "HESS has in the last few years achieved a number of important discoveries concerning high-energy gamma-ray sources in our own Galaxy and has revolutionized high-energy gamma-ray astronomy. These new HESS results illustrate the power of the instrument for extragalactic astronomy and cosmology. The discovery of lower levels of intergalactic starlight has the interesting side effect that the Universe becomes more transparent to gamma rays and that the telescopes can look deeper into the cosmos, increasing their reach for further discoveries!" * Galaxy simulation breaks new ground ------------------------------------- (Institute of Physics Press Release, April 3rd, 2006) (http://www.iop.org/news/1089?rss=2.0) Two astronomers have performed one of the world's largest astrophysics simulations to date in order to model the growth of galaxies. Using the "Earth Simulator" supercomputer in Japan, which is also used for climate modelling and simulating seismic activity, Masao Mori of the University of California at Los Angeles and Masayuki Umemura at the University of Tsukuba have calculated how galaxies evolved from just 300 million years after the Big bang to the present day. The results show that galaxies may have evolved much faster than currently believed (Nature 440 644). According to the "hierarchical" model, galaxies are formed via a bottom-up process that starts with the formation of small clumps of gas and stars that then merge into bigger systems. Mori and Umemura simulated this process using a powerful 3D hydrodynamic code combined with a "spectral synthesis" code for an astrophysical plasma in order to take into account the dynamical and chemical evolution of a primordial galaxy. The Earth-Simulator simulation was performed with an ultra-high resolution based on 1024 "grid points", making it one of the biggest calculations ever performed in astrophysics. Mori and Masayuki set up the initial conditions in their simulation based on a cold dark matter universe, the parameters of which are determined by measurements of the cosmic microwave background. These observations, first made in 2003, show that we are living in a flat universe comprising just 4 percent ordinary matter, 22 percent dark matter and 74 percent dark energy - in agreement with the standard model of cosmology. The researchers then directly compared their numerical results with observations of primitive galaxies called Lyman-alpha emitters and "Lyman break" galaxies, which astronomers find in the most distant and therefore oldest parts of the universe. The results show that the primordial bubbles of gas that formed in the early universe just 300 millions years after the Big Bang do indeed look like Lyman-alpha emitters. After about 1 billion years, the simulations show that these galaxies mutate into Lyman break galaxies. Finally, after 10 billion years of evolution, the structures resemble present-day elliptical galaxies. The simulation also predicts the mixture of chemical elements in the galaxy at each stage of its evolution, and suggests that our Milky Way has roughly the same composition today as it did when it was just 1 billion years old. Until now, galaxies were thought to have evolved gradually and become enriched in heavier elements beyond hydrogen and helium over a period of 10 billion years by repeated star formation and supernova explosions. "Our finding shows that galaxy formation proceeded much faster and that a large amount of heavy elements were produced in galaxies in just 1 billion years," says Mori. 3. SPACE MISSIONS _________________ * New and Improved Antimatter Spaceship for Mars Missions --------------------------------------------------------- (NASA News, April 14th, 2006) (http://www.nasa.gov/centers/goddard/news/topstory/2006/antimatter_spaceship.html) Most self-respecting starships in science fiction stories use antimatter as fuel for a good reason it's the most potent fuel known. While tons of chemical fuel are needed to propel a human mission to Mars, just tens of milligrams of antimatter will do (a milligram is about one-thousandth the weight of a piece of the original M and M candy). However, in reality this power comes with a price. Some antimatter reactions produce blasts of high energy gamma rays. Gamma rays are like X-rays on steroids. They penetrate matter and break apart molecules in cells, so they are not healthy to be around. High-energy gamma rays can also make the engines radioactive by fragmenting atoms of the engine material. The NASA Institute for Advanced Concepts (NIAC) is funding a team of researchers working on a new design for an antimatter-powered spaceship that avoids this nasty side effect by producing gamma rays with much lower energy. Antimatter is sometimes called the mirror image of normal matter because while it looks just like ordinary matter, some properties are reversed. For example, normal electrons, the familiar particles that carry electric current in everything from cell phones to plasma TVs, have a negative electric charge. Anti-electrons have a positive charge, so scientists dubbed them "positrons". When antimatter meets matter, both annihilate in a flash of energy. This complete conversion to energy is what makes antimatter so powerful. Even the nuclear reactions that power atomic bombs come in a distant second, with only about three percent of their mass converted to energy. Previous antimatter-powered spaceship designs employed antiprotons, which produce high-energy gamma rays when they annihilate. The new design will use positrons, which make gamma rays with about 400 times less energy. The NIAC research is a preliminary study to see if the idea is feasible. If it looks promising, and funds are available to successfully develop the technology, a positron-powered spaceship would have a couple advantages over the existing plans for a human mission to Mars, called the Mars Reference Mission. diagram of positron rocket Image left: A diagram of a rocket powered by a positron reactor. Positrons are directed from the storage unit to the attenuating matrix, where they interact with the material and release heat. Liquid hydrogen (H2) circulates through the attenuating matrix and picks up the heat. The hydrogen then flows to the nozzle exit (bell-shaped area in yellow and blue), where it expands into space, producing thrust. Print-resolution copy Credit: Positronics Research, LLC "The most significant advantage is more safety," said Dr. Gerald Smith of Positronics Research, LLC, in Santa Fe, New Mexico. The current Reference Mission calls for a nuclear reactor to propel the spaceship to Mars. This is desirable because nuclear propulsion reduces travel time to Mars, increasing safety for the crew by reducing their exposure to cosmic rays. Also, a chemically-powered spacecraft weighs much more and costs a lot more to launch. The reactor also provides ample power for the three-year mission. But nuclear reactors are complex, so more things could potentially go wrong during the mission. "However, the positron reactor offers the same advantages but is relatively simple," said Smith, lead researcher for the NIAC study. Also, nuclear reactors are radioactive even after their fuel is used up. After the ship arrives at Mars, Reference Mission plans are to direct the reactor into an orbit that will not encounter Earth for at least a million years, when the residual radiation will be reduced to safe levels. However, there is no leftover radiation in a positron reactor after the fuel is used up, so there is no safety concern if the spent positron reactor should accidentally re-enter Earth's atmosphere, according to the team. It will be safer to launch as well. If a rocket carrying a nuclear reactor explodes, it could release radioactive particles into the atmosphere. "Our positron spacecraft would release a flash of gamma-rays if it exploded, but the gamma rays would be gone in an instant. There would be no radioactive particles to drift on the wind. The flash would also be confined to a relatively small area. The danger zone would be about a kilometer (about a half-mile) around the spacecraft. An ordinary large chemically-powered rocket has a danger zone of about the same size, due to the big fireball that would result from its explosion," said Smith. Another significant advantage is speed. The Reference Mission spacecraft would take astronauts to Mars in about 180 days. "Our advanced designs, like the gas core and the ablative engine concepts, could take astronauts to Mars in half that time, and perhaps even in as little as 45 days," said Kirby Meyer, an engineer with Positronics Research on the study. Advanced engines do this by running hot, which increases their efficiency or "specific impulse" (Isp). Isp is the "miles per gallon" of rocketry: the higher the Isp, the faster you can go before you use up your fuel supply. The best chemical rockets, like NASA's Space Shuttle main engine, max out at around 450 seconds, which means a pound of fuel will produce a pound of thrust for 450 seconds. A nuclear or positron reactor can make over 900 seconds. The ablative engine, which slowly vaporizes itself to produce thrust, could go as high as 5,000 seconds. One technical challenge to making a positron spacecraft a reality is the cost to produce the positrons. Because of its spectacular effect on normal matter, there is not a lot of antimatter sitting around. In space, it is created in collisions of high-speed particles called cosmic rays. On Earth, it has to be created in particle accelerators, immense machines that smash atoms together. The machines are normally used to discover how the universe works on a deep, fundamental level, but they can be harnessed as antimatter factories. "A rough estimate to produce the 10 milligrams of positrons needed for a human Mars mission is about 250 million dollars using technology that is currently under development," said Smith. This cost might seem high, but it has to be considered against the extra cost to launch a heavier chemical rocket (current launch costs are about 10,000 dollars per pound) or the cost to fuel and make safe a nuclear reactor. "Based on the experience with nuclear technology, it seems reasonable to expect positron production cost to go down with more research," added Smith. Another challenge is storing enough positrons in a small space. Because they annihilate normal matter, you can't just stuff them in a bottle. Instead, they have to be contained with electric and magnetic fields. "We feel confident that with a dedicated research and development program, these challenges can be overcome," said Smith. If this is so, perhaps the first humans to reach Mars will arrive in spaceships powered by the same source that fired starships across the universes of our science fiction dreams. * NASA Mars Rovers Head for New Sites After Studying Layers ----------------------------------------------------------- (NASA News, April 12th, 2006) (http://www.jpl.nasa.gov/news/news.cfm?release=2006-054) NASA's Mars rover Spirit has reached a safe site for the Martian winter, while its twin, Opportunity, is making fast progress toward a destination of its own. The two rovers recently set out on important -- but very different -- drives after earlier weeks inspecting sites with layers of Mars history. Opportunity finished examining sedimentary evidence of ancient water at a crater called "Erebus," and is now rapidly crossing flat ground toward the scientific lure of a much larger crater, "Victoria." Spirit studied signs of a long-ago explosion at a bright, low plateau called "Home Plate" during February and March. Then one of its six wheels quit working, and Spirit struggled to complete a short advance to a north-facing slope for the winter. "For Spirit, the priority has been to reach a safe winter haven," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the Mars Exploration Rover project. The rovers have operated more than eight times as long as their originally planned three-month explorations on Mars. Each has driven more than 6.8 kilometers (4.2 miles) about 11 times as far as planned. Combined, they have returned more than 150,000 images. Two years ago, the project had already confirmed that at least one place on Mars had a wet and possibly habitable environment long ago. The scientific findings continue. Opportunity spent most of the past four months at Erebus, a highly eroded impact crater about 300 meters (1,000 feet) in diameter, where the rover found extensive exposures of thin, rippled layering interpreted as a fingerprint of flowing water. "What we see at Erebus is a thicker interval of wetted sediment than we've seen anywhere else," said Dr. John Grotzinger of the California Institute of Technology, "The same outcrops also have cracks that may have formed from wetting and drying." In mid-March, Opportunity began a 2-kilometer (1.6-mile) trek from Erebus to Victoria, a crater about 800 meters (half a mile) across, where a thick sequence of sedimentary rocks is exposed. In the past three weeks, Opportunity has already driven more than a fourth of that distance. At Home Plate, Spirit found coarse layering overlain by finer layering in a pattern that fits accumulation of material falling to the ground after a volcanic or impact explosion. In one place, the layers are deformed where a golfball-size rock appears to have fallen on them while they were soft. "Geologists call that a 'bomb sag,' and it is strong evidence for some kind of explosive origin," Squyres said. "We would like to have had time to study Home Plate longer, but we needed to head for a north-facing slope before winter got too bad." Spirit is in Mars' southern hemisphere, where the sun is crossing lower in the northern sky each day. The rovers rely on solar power. The amount available will keep dropping until the shortest days of the Mars winter, four months from now. To keep producing enough electricity to run overnight heaters that protect vital electronics, Spirit's solar panels must be tilted toward the winter sun by driving the rover onto north-facing slopes. However, on March 13 the right-front wheel's drive motor gave out. Spirit has subsequently driven about 80 meters (262 feet) using five wheels and dragging the sixth, but an initial route toward a large hill proved impassable due to soft ground. Last week, the team chose a smaller nearby ridge, dubbed "Low Ridge Haven," as the winter destination. Spirit reached the ridge Sunday and has a favorable 11-degree tilt toward the north. "We have to use care choosing the type of terrain we drive over," Dr. Ashitey Trebi-Ollennu, a rover planner at NASA's Jet Propulsion Laboratory, Pasadena, Calif., said about the challenge of five-wheel driving. In tests at JPL, the team has been practicing a maneuver to gain additional tilt by perching the left-front wheel on a basketball-size rock. Spending eight months or so at Low Ridge Haven will offer time for many long-duration studies that members of the science team have been considering since early in the mission, said Dr. Ray Arvidson of Washington University in St. Louis, deputy principal investigator. These include detailed mapping of rocks and soils; in-depth determination of rock and soil composition; monitoring of clouds and other atmospheric changes; watching for subtle surface changes due to winds; and learning properties of the shallow subsurface by tracking surface-temperature changes over a span of months. * Europe scores new planetary success: Venus Express enters orbit around the Hothouse Planet -------------------------------------------------------------------------------------------- (ESA Press Release, April 11th, 2006) (http://www.esa.int/esaCP/SEM2GQNFGLE_index_0.html) This morning, at the end of a 153-day and 400-million km cruise into the inner Solar System beginning with its launch on 9 November 2005, ESA's Venus Express space probe fired its main engine at 09:17 CEST for a 50-minute burn, which brought it into orbit around Venus. With this firing, the probe reduced its relative velocity toward the planet from 29,000 to about 25,000 km/h and was captured by its gravity field. This orbit insertion manoeuvre was a complete success. During the next four weeks, the Venus Express probe will perform a series of manoeuvres to reach the scheduled operational orbit for its scientific mission. It will move from its current highly elongated 9-day orbit to a 24-hour polar orbit, culminating at 66,000 kilometres. From this vantage point, the orbiter will conduct an in-depth observation of the structure, chemistry and dynamics of the atmosphere of Venus for at least two Venusian days (486 Earth days). Enigmatic atmosphere From previous missions to Venus as well as observations directly from Earth, we already know that our neighbouring planet is shrouded in a thick atmosphere where extremes of temperature and pressure conditions are common. This atmosphere creates a greenhouse effect of tremendous proportions as it spins around the planet in four days in an unexplained 'super-rotation' phenomenon. The mission of Venus Express will be to carry out a detailed characterisation of this atmosphere, using state-of-the-art sensors in order to answer the questions and solve the mysteries left behind by the first wave of explorers. It will also be the first Venus orbiter to conduct optical observations of the surface through 'visibility windows' discovered in the infrared spectrum. The commissioning of the onboard scientific instruments will begin shortly and the first raw data are expected within days. The overall science payload is planned to be fully operational within two months. Europe explores the Solar System With this latest success, ESA is adding another celestial body to its range of Solar System studies. ESA also operates Mars Express around Mars, SMART-1 around the Moon and is NASA's partner on the Cassini orbiter around Saturn. In addition, ESA is also operating the Rosetta probe en route to comet 67P/Churyumov-Gerasimenko. It should reach its target and become the first spacecraft ever to enter orbit around a comet nucleus by 2014. Meanwhile, ESA also plans to complete the survey of our celestial neighbours with the launch of the BepiColombo mission to Mercury in 2013. "With the arrival of Venus Express, ESA is the only space agency to have science operations under way around four planets: Venus, the Moon, Mars and Saturn" underlines Professor David Southwood, the Director of ESA's science programmes. "We are really proud to deliver such a capability to the international science community." "To better understand our own planet, we need to explore other worlds in particular those with an atmosphere," said Jean-Jacques Dordain, ESA Director General. "We've been on Titan and we already are around Mars. By observing Venus and its complex atmospheric system, we will be able to better understand the mechanisms that steers the evolution of a large planetary atmosphere and the change of climates. In the end, it will help us to get better models of what is actually going on in our own atmosphere, for the benefit of all Earth citizens." State-of-the-art science package Venus Express was developed for ESA by a European industrial team led by EADS Astrium incorporating 25 main contractors from 14 European countries. Its design is derived from that of its highly successful predecessor, Mars Express, and its payload accommodates seven instruments including upgraded versions of three instruments developed for Mars Express and two for Rosetta. The PFS spectrometer will determine the temperature and composition profile of the atmosphere at very high resolution. It will also monitor the surface temperature and search for hot spots from possible volcanic activity. The UV/infrared SpicaV/SOIR spectrometer and the VeRa radioscience experiment will probe the atmosphere by observing the occultation of distant starts or the fading of radio signals on the planetary limb. SpicaV/SOIR will be particularly looking for traces of water molecules, molecular oxygen and sulphur compounds, which are suspected to exist in the atmosphere of Venus. The Virtis spectrometer will map the different layers of the atmosphere and provide imagery of the cloud systems at multiple wavelengths to characterise the atmospheric dynamics. On the outer edge of the atmosphere, the Aspera instrument and a magnetometer will investigate the interaction with the solar wind and plasma it generates in an open environment without the protection of a magnetosphere like the one we have around Earth. The VMC wide-angle multi-channel camera will provide imagery in four wavelengths, including one of the 'infrared windows' which will make imaging of the surface possible through the cloud layer. It will provide global images and will assist in the identification of phenomena detected by the other instruments. * New NASA Ames Spacecraft to Look for Ice at Lunar South Pole -------------------------------------------------------------- (NASA News, April 10th, 2006) (http://www.nasa.gov/centers/ames/news/releases/2006/06_21AR.html) NASA today announced that a small, 'secondary payload' spacecraft, to be developed by a team at NASA Ames Research Center, Moffett Field, Calif., has been selected to travel to the moon to look for precious water ice at the lunar south pole in October 2008. The smaller secondary payload spacecraft will travel with the Lunar Reconnaissance Orbiter (LRO) satellite to the moon on the same rocket, the Evolved Expendable Launch Vehicle (EELV), to be launched from Kennedy Space Center, Florida. The NASA Ames team proposed the secondary payload mission, which will be carried out by the Lunar CRater Observation and Sensing Satellite (LCROSS). "The LCROSS mission gives the agency an excellent opportunity to answer the question about water ice on the moon," said Daniel Andrews of NASA Ames, whose team proposed the LCROSS mission. "We think we have assembled a very creative, highly innovative mission, turning the upper stage of the rocket that brought us to the moon into a substantial impactor on the moon." After launch, the secondary payload LCROSS spacecraft will arrive in the lunar vicinity independent of the LRO satellite. On the way to the moon, the LCROSS spacecraft's two main parts, the Shepherding Spacecraft (S-S/C) and the Earth Departure Upper Stage (EDUS), will remain coupled. As the spacecraft approaches the moon's south pole, the upper stage will separate, and then will impact a crater in the south pole area. A plume from the upper stage crash will develop as the Shepherding Spacecraft heads in toward the moon. The Shepherding Spacecraft will fly through the plume, and instruments on the spacecraft will analyze the cloud to look for signs of water and other compounds. Additional space and Earth-based instruments also will study the 2.2-million-pound (1000-metric-ton) plume. Then the Shepherding Spacecraft itself will become an impactor, creating a second plume visible to lunar-orbiting spacecraft and Earth-based observatories. "The LCROSS mission will help us determine if there is water hidden in the permanently dark craters of the moon's south pole," said Marvin (Chris) Christensen, Robotic Lunar Exploration Program (RLEP) manager, and acting director of NASA Ames. "If we find substantial amounts of water ice there, it could be used by astronauts who later visit the moon to make rocket fuel," Christensen added. Earlier, NASA had requested proposals internally from its NASA field centers for existing or reasonably matured concepts for secondary payloads that would offer cost-effective contributions to RLEP. To prepare for the return of astronauts to the moon, NASA will conduct various RLEP robotic missions from 2008 to potentially 2016 to study, to map and to learn about the lunar surface. These early missions will help determine lunar landing sites and whether resources, such as oxygen, hydrogen and metals, are available for use in NASA's long-term lunar exploration objectives. "Establishing research stations on the moon will give us the experience and capabilities to extend to Mars and beyond," noted robotics deputy program manager Butler Hine of Ames. "An exploration science program with a sustained human presence on the moon gives us the opportunity to conduct fundamental science in lunar geology, history of the solar system, physics and the biological response to partial (Earth) gravity," said Christopher McKay, lunar exploration program scientist at Ames. The space agency specified that the winning proposal must demonstrate an affordable concept beneficial to RLEP, according to the document that asked NASA centers to submit suggestions for the secondary payload. NASA noted that the secondary payload mission should cost no more than 80 million dollars. NASA also required that the payload mass not exceed 2,205 pounds (1,000 kilograms). NASA encouraged its field centers to team with industry to develop proposals. On Jan. 10, NASA issued a request for information to industry to allow businesses to provide secondary payload concepts to NASA. Each NASA center reviewed ideas from industry as well as secondary payload concepts developed internally. NASA asked that the concepts advance the Vision for Space Exploration to include missions that evolve lunar science, characterize the lunar environment and support identification sites for future human missions as well as the utility of those sites. The space agency said that it was looking for missions that demonstrate technology that could enhance future exploration, that show operational schemes to support exploration, that develop or emplace infrastructure in support of exploration, that advance commercial opportunities and those missions that would collect engineering data to support the Constellation program. That program is developing NASA's new spaceship, the Crew Exploration Vehicle. * Asteroids: treasures of the past and a threat to the future ------------------------------------------------------------- (ESA Press Release, April 3rd, 2006) (http://www.esa.int/esaCP/SEMC43NFGLE_index_0.html) If a large asteroid such as the recently identified 2004 VD17 about 500 m in diameter with a mass of nearly 1000 million tonnes - collides with the Earth it could spell disaster for much of our planet. As part of ESA's Near-Earth Object deflecting mission Don Quijote, three teams of European industries are now carrying out studies on how to prevent this. ESA has been addressing the problem of how to prevent large Near-Earth Objects (NEOs) from colliding with the Earth for some time. In 1996 the Council of Europe called for the Agency to take action as part of a "long-term global strategy for remedies against possible impacts". Recommendations from other international organisations, including the UN and the Organisation for Economic Cooperation and Development (OECD), soon followed. In response to these and other calls, ESA commissioned a number of threat evaluation and mission studies through its General Studies Programme (GSP). In July 2004 the preliminary phase was completed when a panel of experts appointed by ESA recommended giving the Don Quijote asteroid-deflecting mission concept maximum priority for implementation. Now it is time for industry to put forward their best design solutions for the mission. Following an invitation to tender and the subsequent evaluation process, three industrial teams have been awarded a contract to carry out the mission phase-A studies. a team with Alcatel Alenia Space as prime contractor includes subcontractors and consultants from across Europe and Canada; Alcatel Alenia Space developed the Huygens Titan probe and is currently working on the ExoMars mission a consortium led by EADS Astrium, which includes Deimos Space from Spain and consultants from several European countries, brings their experience of working on the design of many successful ESA interplanetary missions such as Rosetta, Mars and Venus Express a team led by QinetiQ (UK), which includes companies and partners in Sweden and Belgium, draws on their expertise in mini and micro satellites including ESA's SMART-1 and Proba projects This month the three teams began work and a critical milestone will take place in October when the studies will be reviewed by ESA with the support of an international panel of experts. The results of this phase will be available next year. No reason for panic yet The risk is still small however, and may decrease even further when new observations are carried out. Still, if this or any other similar-sized object, such as 99942 Apophis, an asteroid that will come close enough to the Earth in 2029 to be visible to the naked eye, collided with our planet the energy released could be equivalent to a significant fraction of the world's nuclear arsenal, resulting in devastation across national borders. Luckily, impacts with very large asteroids are uncommon, although impacts with smaller asteroids are less unlikely and remote in time. In 1908 an asteroid that exploded over Siberia devastated an unpopulated forest area of more than 2000 km2; had it arrived just a few hours later, Saint Petersburg or London could have been hit instead. Fossils of the Solar System Asteroids are a part of our planet's history. As anyone visiting the Barringer Meteor Crater in Arizona, USA or aiming a small telescope at the Moon can tell, there is plenty of evidence that the Earth and its cosmic neighbourhood passed through a period of heavy asteroid bombardment. On the Earth alone the remains of more than 160 impacts have been identified, some as notorious as the Chicxulub crater located in Mexico's Yucatan peninsula, believed to be a trace of the asteroid that caused the extinction of the dinosaurs 65 million years ago. Collisions have shaped the history of our Solar System. Because asteroids and comets are remnants of the turbulent period in which the planets were formed, they are in fact similar to 'time capsules' and carry a pristine record of those early days. By studying these objects it is possible to learn more about the evolution of our Solar System as well as 'hints' about the origins of life on Earth. Comet 67P/Churyumov-Gerasimenko is one of these primitive building blocks and will be visited by ESA's Rosetta spacecraft in 2014, as a part of a very ambitious mission - the first ever to land on a comet. Rosetta will also visit two main belt asteroids (Steins and Lutetia) on its way to comet 67P/Churyumov-Gerasimenko. The mission will help us to understand if life on Earth began with the help of materials such as water and organisms brought to our planet by 'comet seeding'. ESA's Science programme is already looking at future challenges, and its Cosmic Vision 2015-2025 plan has identified an asteroid surface sample return as one of the key developments needed to further our understanding of the history and composition of our Solar System. Work still in progress Asteroids and comets are fascinating objects that can give or take life on a planetary scale. Experts around the world are putting all their energy and enthusiasm into deciphering the mysteries they carry within them. With an early launch provisionally scheduled for 2011, Don Quijote will serve as a 'technological scout' not only to mitigate the chance of the Earth being hit by a large NEO but also for the ambitious journeys to explore our solar system that ESA will continue to embark upon. The studies now being carried out by European industry will bring the Don Quijote test mission one step nearer.