Space cargo ship near completion

 

By Jonathan Amos Science reporter, BBC News The last fuelling procedure begins on Friday morning The launch and docking windows for the ATV, Europe's huge new space-station resupply ship, have been set. The Automated Transfer Vehicle (ATV) will be lofted in the 22 February to 8-9 March timeframe, European Space Agency (Esa) officials say. The 20-tonne vessel will then attach itself to the international outpost during one of two windows; in early March, or in late March to early April. ATV is the biggest, most sophisticated spacecraft Europe has attempted to fly. Its preparation at the Kourou spaceport in French Guiana is very nearly complete. This Friday, engineers will start the final stage of fuelling, adding 2.7 tonnes of oxidiser to the ship's propellant system. Once this is done, and major headway has been made on the final 200 or so items on an "open work list", the ATV will be moved out of Kourou's giant S5 integration halls and taken to the Baf (Final Assembly Building) where it will be mated with its Ariane 5 launcher. SPACE STATION CARGO TRUCKS Mission Guide: Jules Verne ATV (l) will resupply the ISS with up to 7,500kg of cargo Capacity is three times that of the Russian Progress craft (r) Deliveries will include science equipment, food and clothing Large tanks can transport vital air, water and fuel supplies ATV project's estimated cost is about 1.3bn euros (£0.9bn) At least four craft will follow the maiden ATV - Jules Verne Named after the author who wrote about fantastic journeys   "We are on schedule," said Nicolas Chamussy, ATV programme manager for prime contractor EADS Astrium. "Since October, we have lost just three days in the planning. We have some 200 actions still to do, but these are normal; I don't see major issues," he told BBC News. Last week, at a general designers' review in Moscow, the Russians (one of the major partners in the space station project) gave their formal approval for the mission to proceed. A similar meeting will be held in the US this week at which the Americans are also expected to sign off ATV. A gathering of space agency officials on 6 February will then begin the process of narrowing the launch window to a specific date. Much will depend on what happens to the shuttle Atlantis. It is scheduled to fly to the International Space Station on 7 February. If it is held on the ground because of bad weather or further technical problems, the ATV launch date may start to creep to the back of its window. But when ATV lifts off is probably not so important as when it arrives. It cannot dock when the shuttle is present or in flight - not least because the two vehicles both make use of the US Tracking and Data Relay Satellite System. "We have built ATV to be almost independent of a lot of the other operations," explained John Ellwood, Esa's ATV mission manager.                                                          ATV flight animation There are about 200 - mostly simple - tasks still to perform "We have a lot of flexibility in when we actually dock. We will launch as soon as ATV is ready, the launcher is ready and the ground segment is ready. "We then go to the space station and we have the option of immediately docking if conditions are right or we could loiter. We have a strategy where we go to a point 2,000km in front of the space station and just wait there." The best times to dock are 15-19 March and 30 March to 5 April. These are periods when the station's alignment to the Sun will give astronauts a clear view of the ATV's approach; cameras will not be blinded by bright light. Once attached, the ATV - dubbed Jules Verne for its first flight - will stay on-station until August, after which it will be commanded to undock and ditch itself in the Pacific. Preparation work on the second ATV, likely to fly in 2010, has already begun. Jonathan.Amos-INTERNET@bbc.co.uk

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MESSENGER at Mercury

For the first time in more than 30 years, a spacecraft has returned to Mercury, providing images from sections of the planet that have never been viewed by a spacecraft.

Provided by the Johns Hopkins University

The top left image was taken when MESSENGER was about 21,000 miles from Mercury, and the bottom right image was snapped from a distance of about 250,000 miles. NASA/JHUAPL/Carnegie Institution of Washington [View Larger Image] Updated January 28, 2008 After MESSENGER completed its successful flyby of Mercury, the Narrow Angle Camera (NAC), part of the Mercury Dual Imaging System (MDIS), took images of the receding planet. Beginning on January 14, 2008, about 100 minutes after MESSENGER's closest pass by the surface of Mercury, until January 15, 2008, about 19 hours later, the NAC acquired one image every four minutes. In all, 288 images were snapped during this sequence; shown here are just 12 of those departing shots. This large set of departing NAC images has been assembled into a movie, which will be shown today during a NASA press conference at 1 pm EST.

The width of this image is about about 125 miles (200 kilometers), showing that these scarps can be hundreds of miles long on Mercury. NASA/JHUAP/Carnegie Institution of Washington [View Larger Image] Updated January 27, 2008 As the MESSENGER team continues to study the high-resolution images taken during the Mercury flyby encounter on January 14, 2008, scarps (cliffs) that extend for long distances are discovered. This frame, taken by the Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS), shows a region of Mercury's surface previously unseen by spacecraft and a large scarp crossing vertically through the scene, on the far right of the image. This scarp is the northern continuation of the one seen in the NAC image released on January 16. The presence of many long and high scarps, as discovered from pictures from the Mariner 10 mission in 1974 and 1975, suggests a history for Mercury that is unlike that of any of the other planets in the solar system. These giant scarps are believed to have formed when Mercury's interior cooled and the entire planet shrank slightly as a result. However, Mariner 10 was able to view less than half the planet, so the global extent of these scarps has been unknown. MESSENGER images, like this one, are providing the first high-resolution looks at many areas on Mercury's surface, and science team members are busy mapping these newly discovered scarps to see whether they are common everywhere on the planet.

This image was acquired about 94 minutes after MESSENGER's closest approach to Mercury, when the spacecraft was at a distance of about 20,000 miles (32,000 kilometers). NASA/JHUAP/Carnegie Institution of Washington [View Larger Image] Updated January 26, 2008 As MESSENGER sped by Mercury on January 14, 2008, the Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS) captured this shot looking toward Mercury's north pole. The surface shown in this image is from the side of Mercury not previously seen by spacecraft. The top right of this image shows the limb of the planet, which transitions into the terminator (the line between the sunlit, day side and the dark, night side) on the top left of the image. Near the terminator, the Sun illuminates surface features at a low angle, casting long shadows and causing height differences of the surface to appear more prominent in this region. It is interesting to compare MESSENGER's view to the north with the image looking toward the south pole, released on January 21. Comparing these two images, it can be seen that the terrain near the south pole is more heavily cratered while some of the region near the north pole shows less cratered, smooth plains material, consistent with the general observations of the poles made by Mariner 10. MESSENGER acquired over 1200 images of Mercury's surface during its flyby, and the MESSENGER team is busy examining all of those images in detail, to understand the geologic history of the planet as a whole, from pole to pole.

This image of Mercury's surface is about 600 miles (1000 kilometers) across. NASA/JHUAP/Carnegie Institution of Washington [View Larger Image] Updated January 25, 2008 During MESSENGER's flyby of Mercury on January 14, 2008, part of the planned sequence of observations included taking images of the same portion of Mercury's surface from five different viewing angles. The first view from this sequence was taken just after MESSENGER made its closest approach to Mercury, from a low viewing angle; an image of the first view was released on January 19. The image released here, acquired with the Wide Angle Camera (WAC) on the Mercury Dual Imaging System (MDIS), was snapped 13 minutes after MESSENGER's closest approach with Mercury. The lower two-thirds of this image shows much of the same terrain seen in the first view, but from a much higher viewing angle, as the spacecraft began to pass nearly overhead. At the time of this image, MESSENGER was at a distance of about about 2000 miles (3000 kilometers) from Mercury. A comparison of the images taken at different viewing angles provides important information about the properties of the materials that make up Mercury's surface. In addition, each view was taken through all 11 of the WAC's narrow-band color filters. The image shown here is from filter 7, which is sensitive to light near the red end of the visible spectrum (750 nm). The MESSENGER team is working to compare these images taken from different perspectives and in different colors to understand surface properties on Mercury. In addition, knowledge of the variation of image properties with viewing angle in this region will permit a more confident comparison of images of other portions of the surface taken at different illumination and viewing angles.

Experience MESSENGER's Mercury flyby virtually Planetary scientists have sent the MESSENGER space probe to Mercury to answer questions left hanging after the visit of the last spacecraft, Mariner 10, in the mid-1970s. NASA / JHUAPL / CIW [View Larger Image] See Mercury through the "eyes" of MESSENGER's imagers with the Mercury Flyby Visualization Tool. This new web feature offers a unique opportunity to see simulated views of Mercury from MESSENGER's perspective during approach, flyby, and departure, or in real-time (as the observations actually occur). This tool combines the best available image map of Mercury's surface with observation sequences for the Mercury Dual Imaging System (MDIS), Mercury Atmospheric and Surface Composition Spectrometer (MASCS), and Mercury Laser Altimeter (MLA). The map of Mercury's surface combines Earth-based low-resolution radar images from the Arecibo Observatory in Puerto Rico and image mosaics from the Mariner 10 spacecraft flybys of Mercury in 1974 and 1975.

This image shows just a portion (276 kilometers, or 172 miles, wide) of one frame taken with the Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS). In this image alone, 763 craters have been identified and measured (shown in green) along with 189 hills (shown in yellow). Altogether, 491 frames were taken by the NAC to create high-resolution mosaics of Mercury's surface. NASA/JHUAP/Carnegie Institution of Washington [View Larger Image] Updated January 24, 2008 On January 14, 2008, MESSENGER flew by Mercury and snapped images of a large portion of the surface that had not been previously seen by spacecraft. Ever since the first images were received back on Earth one day later, January 15, MESSENGER team members have been closely examining and studying this "new" terrain with great interest and excitement. One of many investigations underway includes identifying and measuring the impact craters on these previously unseen regions. The density of craters on the surface of a planet can be used to indicate the relative age of different places on the surface; the more craters the surface has accumulated, the older the surface. By counting craters on different areas of Mercury's surface, a relative geologic history of the planet can be constructed, indicating which surfaces formed first and which formed later. However, this process is also time consuming; Mercury has a lot of craters! Of course, simply counting the craters is not enough. Each crater has to be measured and classified to fully interpret the differences in crater density. Many small craters form as "secondaries," as clumps of material ejected from a "primary" crater re-impact the surface in the regions surrounding the primary. In order to learn about the history of asteroid and comet impacts on Mercury, scientists have to distinguish between the primary and secondary craters. Once many more craters are measured, MESSENGER researchers will have new insights into the geological history of Mercury.

This color image shows the Matisse crater. NASA/JHUAP/Carnegie Institution of Washington [View Larger Image] Updated January 23, 2008 As the MESSENGER spacecraft approached Mercury on January 14, 2008, the Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS) snapped this image of the crater Matisse. Named for the French artist Henri Matisse, Matisse crater was imaged during the Mariner 10 mission and is about 130 miles (210 kilometers) in diameter. Matisse crater is in the southern hemisphere and can be seen near the terminator of the planet (the line between the sunlit, day side and the dark, night side) in both the color and single-filter, black-and-white images released previously that show an overview of the entire incoming side of Mercury. On Mercury, craters are named for people, now deceased, who have made contributions to the humanities, such as artists, musicians, painters, and authors. The International Astronomical Union (IAU) oversees the official process of naming new craters and other new features discovered on bodies throughout the solar system. Scientists studying and mapping unnamed features can suggest names for consideration by the IAU. The 1213 images taken by MESSENGER during its first flyby encounter with Mercury cover a large region of Mercury's surface previously unseen by spacecraft, revealing many new craters and other features that will need to be named.

This visible-infrared image shows an incoming view of Mercury, about 80 minutes before MESSENGER's closest pass of the planet on January 14, 2008, from a distance of about 27,000 kilometers (17,000 miles). NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image] Updated January 22, 2008 One week ago, the MESSENGER spacecraft transmitted to Earth the first high-resolution image of Mercury by a spacecraft in over 30 years, since the three Mercury flybys of Mariner 10 in 1974 and 1975. MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band color filters, in contrast to the two visible-light filters and one ultraviolet filter that were on Mariner 10's vidicon camera. By combining images taken through different filters in the visible and infrared, the MESSENGER data allow Mercury to be seen in a variety of high-resolution color views not previously possible. MESSENGER's eyes can see far beyond the color range of the human eye, and the colors seen in the accompanying image are somewhat different from what a human would see. The color image was generated by combining three separate images taken through WAC filters sensitive to light in different wavelengths; filters that transmit light with wavelengths of 1000, 700, and 430 nanometers (infrared, far red, and violet, respectively) were placed in the red, green, and blue channels, respectively, to create this image. The human eye is sensitive across only the wavelength range 400 to 700 nanometers. Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in the single-filter, black-and-white image released last week. Image sequences acquired through the 11 different MDIS filters are being used to distinguish subtle color variations indicative of different rock types. By analyzing color differences across all 11 filters, the MESSENGER team is investigating the variety of mineral and rock types present on Mercury's surface. Such information will be key to addressing fundamental questions about how Mercury formed and evolved. Mercury has a diameter of about 3030 miles (4880 kilometers), and the smallest feature visible in this color image is about 6 miles (10 kilometers) in size.

This image was acquired about 98 minutes after MESSENGER's closest approach to Mercury, when the spacecraft was at a distance of about 21,000 miles (33,000 kilometers). NASA/JHUAPL/CWI [View Larger Image] Updated January 21, 2008 One week ago, on January 14, 2008, MESSENGER passed 124 miles (200 kilometers) above the surface of Mercury and snapped the first pictures of a side of Mercury not previously seen by a spacecraft. The image to the right shows that previously unseen side, with a view looking toward Mercury's south pole. The southern limb of the planet can be seen in the bottom right of the image. The bottom left of the image shows the transition from the sunlit, day side of Mercury to the dark, night side of the planet, a transition line known as the terminator. In the region near the terminator, the sun shines on the surface at a low angle, causing the rims of craters and other elevated surface features to cast long shadows, accentuating height differences in the image. This image is just one in a planned sequence of 42 images acquired by the Narrow Angle Camera of the Mercury Dual Imaging System (MDIS). From these 42 images, the MESSENGER team is creating a high-resolution mosaic image of this previously unseen portion of Mercury. During the flyby, MDIS took more than 1,200 images, which are being combined to create multiple mosaics with different resolutions and of different portions of the planet. The creation of high-resolution mosaic images will enable a global view of Mercury's surface and will be used to understand the geologic processes that made Mercury the planet we see today.

This picture provides a global context for the MDIS Narrow Angle Camera (NAC) images taken while MESSENGER was inbound. This image was taken about 80 minutes before closest approach from a distance of about 17,000 miles (27,000 kilometers) and shows features as small as 6 miles (10 kilometers). NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image] Updated January 18, 2008 As MESSENGER neared Mercury on January 14, 2008, the spacecraft's Wide Angle Camera on the Mercury Dual Imaging System (MDIS) took images of the planet through each of its 11 filters. This image of the planet's full crescent was taken using the 7th filter, in light near the far-red end of the visible spectrum (750 nm). The image shows portions of Mercury previously seen by Mariner 10, but when Mariner 10 flew by the planet at each of its encounters the Sun was nearly overhead. For this MESSENGER flyby, in contrast, the Sun is shining obliquely on regions near the day/night boundary (called the terminator) on the right-hand side of the crescent, revealing the surface topography in sharp relief. This image illustrates how MESSENGER, during its future flybys and subsequent orbital mission, will teach us much about the portion of Mercury already imaged by Mariner 10, and not just because of its superior camera and close proximity to the planet. The solar lighting geometry makes an enormous difference. A day after its successful flyby of Mercury, the MESSENGER spacecraft turned toward Earth on Tuesday and began downloading the 500 megabytes of data that had been stored on the solid-state recorder during the encounter. All of those data, including 1,213 images from the Mercury Dual Imaging System (MDIS) cameras, have now been received by the Science Operations Center at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. Preliminary analysis of these data by the MESSENGER Science Team has confirmed that all seven MESSENGER instruments are healthy and operated as planned during the flyby. As MESSENGER flew by the planet, it missed its targeted aim point by only 5.12 miles (8.25 kilometers), affording the critical gravity assist needed to continue on a course to become, in 2011, the first spacecraft ever to orbit Mercury. During this first encounter, the payload successfully conducted a carefully orchestrated sequence of observations designed to take full advantage of the geometry of the flyby trajectory and to optimize the science return from each instrument. In addition to images of the previously unseen portion of the planet's surface, measurements were made that will contribute to the characterization of all aspects of Mercury and its environment, from its metallic core to the far reaches of its magnetosphere. "We have one excited science team," says MESSENGER Project Manager, Peter D. Bedini, of APL, "and their enthusiasm is contagious." The analysis of these data is just beginning, but there are already indications that new discoveries are at hand.

The image shows a variety of surface textures, including smooth plains at the center of the image, many impact craters (some with central peaks), and rough material that appears to have been ejected from the large crater to the lower right. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image] Updated January 17, 2008 As the MESSENGER spacecraft drew closer to Mercury for its historic first flyby, the spacecraft's Narrow Angle Camera (NAC) on the Mercury Dual Imaging System (MDIS) acquired an image mosaic of the sunlit portion of the planet. This image is one of those mosaic frames and was acquired on January 14, 2008, when the spacecraft was about 11,000 miles (18,000 kilometers) from the surface of Mercury, about 55 minutes before MESSENGER's closest approach to the planet. This large 120 miles (about 200 milometers) crater was seen in less detail by Mariner 10 more than 3 decades ago and was named Sholem Aleichem for the Yiddish writer. In this MESSENGER image, it can be seen that the plains deposits filling the crater's interior have been deformed by linear ridges. The shadowed area on the right of the image is the day-night boundary, known as the terminator. Altogether, MESSENGER acquired over 1200 images of Mercury, which the science team members are now examining in detail to learn about the history and evolution of the innermost planet.

This MESSENGER image was taken from a distance of about 11,000 miles (18,000 kilometers), about 56 minutes before the spacecraft's closest encounter with Mercury. It shows a region roughly 300 miles (500 km) across, and craters as small as 0.6 mile (1 km) can be seen in the image above. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image] Updated January 16, 2008 As MESSENGER approached Mercury on January 14, 2008, the spacecraft's Narrow-Angle Camera on the Mercury Dual Imaging System (MDIS) instrument captured this view of the planet's rugged, cratered landscape illuminated obliquely by the Sun. The large, shadow-filled, double ringed crater to the upper right was glimpsed by Mariner 10 more than three decades ago and named Vivaldi, after the Italian composer. Its outer ring has a diameter of about about 125 miles (200 kilometers). MESSENGER's modern camera has revealed detail that was not well seen by Mariner 10, including the broad ancient depression overlapped by the lower-left part of the Vivaldi crater. The MESSENGER science team is in the process of evaluating later images snapped from even closer range showing features on the side of Mercury never seen by Mariner 10. It is already clear that MESSENGER's superior camera will tell us much that could not be resolved even on the side of Mercury viewed by Mariner's vidicon camera in the mid-1970s.

The MESSENGER spacecraft snapped this image yesterday morning from a distance of 470,000 miles (760,000 km). The image has a resolution of about 12 miles (20 km) per pixel. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington [View Larger Image] Updated January 14, 2008 NASA's MESSENGER spacecraft is on track for its first flyby of Mercury today. The craft will explore the planet from as close as 125 miles (200 kilometers). The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) craft, launched August 3, 2004, will be the first spacecraft to study the innermost planet while in orbit around it. Following three flybys during the next 3 years, MESSENGER will reach orbit around Mercury in 2011. Planetary scientists are eager to get a closer look at the Sun's nearest neighbor. "We are about to visit Mercury for the first time in more than 30 years, and we can't wait," says MESSENGER principal investigator Sean Solomon of the Carnegie Institution of Washington. NASA's Mariner 10 is the only other spacecraft to visit the planet closest to the Sun. "We'll be making close-in observations of the composition of Mercury's surface and atmosphere, and we'll be probing deeper into the planet's magnetosphere than we've ever been," says Solomon. The MESSENGER probe's Mercury Dual Imaging System cameras began snapping pictures of the planet January 9. NASA plans a mission update on the Mercury flyby January 30. Visit MESSENGER's online newsroom.

January 8, 2008 On January 9, MESSENGER's Mercury Dual Imaging System cameras began gathering pictures of Mercury as the probe zeros in on the planet. "With just one week to go before the flyby, the spacecraft is on target to encounter the planet at an altitude of 202 kilometers," says Mission Systems Engineer Eric Finnegan of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. "All subsystems and instruments are operating nominally and configured for the start of the flyby sequence, except for the Mercury Laser Altimeter and part of the Gamma-Ray Spectrometer, which we'll turn on just before the flyby." Over the next week, the team will make final flyby preparations and upload the final command sequences for the encounter. "We are about to visit Mercury for the first time in more than 30 years, and we can't wait," says MESSENGER Principal Investigator Sean Solomon of the Carnegie Institution of Washington. "In addition to providing the critical gravity assist that will move MESSENGER along its path toward Mercury orbit insertion in March 2011, this flyby will let us see parts of Mercury never before viewed by spacecraft. We'll be making close-in observations of the composition of Mercury's surface and atmosphere, and we'll be probing deeper into the planet's magnetosphere than we've ever been. We expect many surprises." On December 19th, MESSENGER's 19th trajectory correction maneuver (TCM-19) changed the spacecraft's velocity by 3.6 feet per second (1.1 meters per second), directing MESSENGER closer to its intended target for the first flyby. TCM-19 went so well that the mission design and navigation teams have decided that a TCM scheduled for January 10 will not be needed. "Cancellation of this maneuver is a demonstration of the near-perfect execution of TCM-19 just prior to the start of the holiday season," says Finnegan.

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Space Rock Misses Mars, Barely

 

By Jeremy Hsu Staff Writer posted: 30 January 2008 06:42 am ET

An asteroid once thought to be on a collision course with Mars passed the Red Planet today without incident.

Astronomers first estimated that asteroid 2007 WD5 had as high as a 3.6 percent chance of striking the planet. Newer observations kept lowering the odds for the 164-foot space rock until Jan. 9, when NASA's Near-Earth Object (NEO) program office effectively ruled out chances of an impact.

"Mars sees these kinds of near-miss encounters every ten or twenty years, but the impact rate for asteroids this size is about once in a thousand years," said Steve Chesley, an astronomer at the Jet Propulsion Lab in Pasadena, California.

Astronomers had hoped the fleet of spacecraft orbiting Mars would get a chance to observe the asteroid plowing into the Martian surface. The subsequent crater would have roughly equaled the size of the Meteor Crater that formed in northern Arizona 50,000 years ago, with a 0.5-mile diameter. Such an impact would have also allowed scientists to study the dust cloud from the impact.

"We were hoping for a spectacular show to reveal a lot," Chesley said. "We've actually never seen a significant impact on a terrestrial planet."

Mars is a smaller and harder target for space rocks to hit when compared with Earth, but about five times as many asteroids cross the Martian orbit, according to Chesley. 2007 WD5's path around the sun ranges from just outside Earth's orbit to the outer edge of the asteroid belt between Mars and Jupiter, but will not impact with either Mars or Earth in the next century, JPL researchers said.

The asteroid missed Mars by a distance of approximately 6.5 Mars radii.

Similar near misses occur with Earth. And similarly, astronomers sometimes give odds on a possible impact and then, with further observations, reduce the odds to zero.

In fact, the Mars flyby occurred a day after a 500-foot asteroid flew by Earth at a distance somewhat greater than from the Earth to the Moon.

Chesley and other astronomers considered having one of the Martian rovers eyeball the passing 2007 WD5, but judged the task too difficult for the robotic explorers. None of the orbiting spacecraft turned their cameras or other equipment on the passing rock, either.

"After we knew it was going to miss, it's really a pretty ordinary asteroid cruising around the solar system," Chesley said.

• VIDEO: Killer Comets and Ominous Asteroids
• IMAGES: Impact Craters on Earth and Beyond
• VIDEO: Bootprints on Asteroids
  

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Dust Strangely Vaporized by Stellar Explosion

 

By Clara Moskowitz Staff Writer posted: 28 January 2008 06:05 am ET

Explosions of small stars, long thought to create stellar dust, actually sweep dust away, scientists discovered.

For years, researchers have observed swirling dust clouds around systems called recurring novas, which periodically explode. New images of a distant nova have now overturned astronomers' long-standing assumption that the dust originates in the blasts.

Scientists recently observed the RS Ophiuchi system, where a small white dwarf star and large red giant orbit each other. Over time, the giant sheds its outer layer of gas, which the dwarf sweeps up. The little star's mass grows gradually, eventually reaching a tipping point, when the top layer ignites in a thermonuclear explosion and expels the surface into space. The process then starts over — astronomers have already seen this system "go nova" in 1898, 1933, 1958, 1967 and 1985.

When RS Ophiuchi blew again in February 2006, researchers took advantage of a new instrument, called the Keck Nuller, at the W. M. Keck Observatory in Mauna Kea, Hawaii, to watch the event in action. The Nuller used two giant telescopes to block out the overwhelming light from the explosion so scientists could study its fainter surroundings.

They were surprised to see no dust in the bright zone around the star and only to see dust farther away, where the blast wave had not yet reached. The researchers surmised that the detonation had vaporized nearby dust particles, and that the outer dust must have been created before the bang.

"This flies in the face of what we expected," said Richard Barry, an astronomer at NASA's Goddard Space Flight Center in Greenbelt, Md., who headed up the observations. "Astronomers had previously thought that nova explosions actually create dust."

The team suspects the dust is really produced when the white dwarf plows through the red giant's trail of debris, creating patches of gas where atoms are cool and dense enough to clump together into dust particles.

The findings will be detailed in the May 1 issue of the Astrophysical Journal.

• Top 10 Star Mysteries
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Hyperfast Star Ejected from the Large Magellenic Cloud

Written by Nicholos Wethington

Occasionally, stars minding their own business around the supermassive black hole at the center of our galaxy get chucked out of the Milky Way, never to return. Fraser wrote about the discovery of two of these exiled stars, hurling away at the mind-blowing speed of over 1 million miles an hour. A recent study of another shows that not all of them originate in the center of our own galaxy.
New results from astronomers at the Carnegie Institute show that one star rocketing away from the Milky Way hearkens from the Large Magellanic Cloud, our neighboring galaxy. There have been ten such hypervelocity stars discovered, but where this one came from was quite a conunudrum.
Named HE 0437-5439, it's nine times the mass of the Sun, and is traveling at 1.6 million miles an hour (2.6 million km an hour). The origin of the star has been a mystery until now because of its youth: it is 35 million years old, but it would have taken 100 million years to get to its current location if it were from the center of the Milky Way.
This meant that the star either came from somewhere else, or had to have formed out of the merger of two low-mass stars from the Milky Way, a so-called "blue straggler."
Carnegie astronomers Alceste Bonanos and Mercedes López-Morales, and collaborators Ian Hunter and Robert Ryans from Queen's University Belfast took measurements of the composition of the star – the first time this has been done on any hypervelocity star – and determined that its metal-poor makeup pointed towards the Large Magellanic Cloud as the former home of the castaway.
Bonanos said,"We've ruled out that the star came from the Milky Way. The concentration of [heavy] elements in Large Magellanic Cloud stars are about half those in our Sun. Like evidence from a crime scene, the fingerprints point to an origin in the Large Magellanic Cloud."
Hypervelocity stars get their kick of energy from their interaction with a black hole. The stars were once part of a binary system, and as one star in the system gets captured by the black hole, the other is abruptly released, booting it clear out of the galaxy.
The mere fact that the Large Magellanic Cloud produced this hyperfast star hints at the presence of a black hole there, which has never previously been observed to exist.
Source: Carnegie Institute Press Release

Filed under: Astronomy, Black Holes

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UK Astronomy Community "Deliberately Sabotaged" By Funding Cuts To Gemini Observatories

Written by Ian O'Neill


UK astronomers have been dealt a serious and unexpected blow. Funding cuts to space research has stopped the nation from continuing its work at the Gemini observatories in Hawaii and Chile. The UK helped to build the 8.1 meter telescopes and have ploughed £70 million ($140 million) to date into the construction and development of the sites since the late 1990's. In an effort to plug a £80 million ($160 million) deficit in space research funding, the Science and Technology Facilities Council (STFC) has signalled to researchers that the UK will be pulling out of the project, leaving astronomers bemused and angry.

Next month, the UK's involvement in the multi-national Gemini project will end. After a decade of construction and research, the world's most advanced telescopes will lose one of their most influential donors as the STFC has declared the British involvement in the project surplus to the government's vision for the future of UK science. This decision will leave the US, Canada, Chile, Australia, Brazil and Argentina to continue astronomy without their 23.8% shareholder. The move has bewildered astronomers as the Gemini project is considered to be one of the most successful international collaborations in recent years, allowing the seven nation "science club" to observe both hemispheres' night sky with unparalleled clarity.

"To withdraw from the state-of-the-art Gemini facilities leaves the UK ground-based astronomy strategy in disarray - some would say deliberately sabotaged." - Professor Paul Crowther, Sheffield University, UK.

This move by the STFC highlights the recent turbulence in physics funding. After the merger of two of the largest research councils in the UK, the Particle Physics and Astronomy Research Council (PPARC) and the Central Laboratory of the Research Councils (CCLRC), the STFC was formed and inherited the unenviable task to find the money to cover the research funding deficit. New prestige facilities such as the Diamond Synchrotron, in Oxfordshire, are over-budget and the shortfall has to be found elsewhere. Requests have been made to the UK government for more funds, but the request has fallen on deaf ears. International research has therefore suffered, with more cuts in astronomy, particle physics and laser optics forecast. Jobs will be lost and the prediction is that the UK will have some of the most advanced physics research centers, but with no scientists to do the research.
The Gemini project is just one of the recent casualties during these dim times for UK physics. A campaign website outlining all the recent cutbacks by the STFC funding crisis has been set up to bring attention to the spiralling problem. The banner reads: "International Year Of Astronomy, 2009 (unless you're from the UK*). The Universe - Yours To Discover. *All we could afford was this logo." - STFC Funding Crisis: Astronomy.

Worrying times for the UK, and international physics as a whole.
Sources: BBC website

Filed under: Observatories

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Gravity: the 'Holy Grail' of physics

By Dr Brian Cox Presenter, BBC Horizon: What on Earth is wrong with gravity? Newton's concept of gravity has problems, says Brian Cox Isaac Newton wrote down his theory of gravity in 1689, and his equations are used to this day to send space probes to the outer edges of our Solar System. So what could possibly be wrong with our understanding of it? There are problems with Newton's theory, however. It doesn't quite describe the orbit of Mercury, the closest planet to the Sun, and as Newton knew very well it has nothing to say about what the force of gravity actually is. It took over 200 years and the genius of Albert Einstein to discover a deeper theory. Einstein's General Theory of Relativity describes the force we see as gravity as being due to the bending and curving of space and time (or to be more accurate "space-time") by heavy objects like the Earth and Sun. Curved space-time This is a bizarre concept, but many of us use Einstein's theory everyday when we jump in our cars and turn on the satellite navigation system. Astonishingly, the fact that the Earth bends time has to be taken into account, otherwise our sat-navs would drift by 11km per day. Einstein's theory of curved space-time beautifully predicts the orbit of Mercury, and much more extreme phenomena out in the Universe. The Ligo observatories aim to detect gravitational waves Perhaps the most extreme test of Einstein comes in the from of binary pulsars: two stars as massive as the Sun but squashed to the size of a city, orbiting each other thousands of times a second. Einstein predicts that these exotic stars should spiral inwards towards each other as they release energy in the form of gravitational waves. Changes in the violent dance of the binary pulsars have been observed at exactly the rate predicted by Einstein, but the gravitational waves themselves have yet to be seen. This is the goal of the Ligo observatories near Seattle and New Orleans. Gravitational waves as predicted by Einstein are one of the strangest phenomena in nature. Broken theory They are a travelling, stretching and squashing of space and time! If they exist, they will be passing through you right now as you read this, speeding up and slowing down your watch and stretching and squashing your head, fortunately by an amount less than the size of a sub-atomic particle. Einstein's laws must break down in the hearts of black holes So you don't feel them, but, remarkably, Ligo may see their effects. The observation of gravitational waves would be another remarkable triumph for Einstein, but even that will not satisfy physicists like myself. This is because we know that there are places in the Universe where Einstein must fail. In the heart of black holes, giant suns collapsed to a single infinitely dense point, Einstein breaks down. And even more crucially, back at the beginning of time, the Big Bang itself, Einstein's picture of space and time is no longer adequate. We physicists are therefore faced with a deep problem. If we want to truly understand how, and maybe even why, the Universe began, then we must know what space and time looked like right back at the beginning. Such a theory, if it exists, would be what is known as a quantum theory of gravity - a theory that supersedes Einstein and works not only in the world of planets, stars and galaxies, but also in the sub-atomic sized world of black holes and the very beginning of the Universe itself. This quest is the "Holy Grail" of 21st century physics. Dr Brian Cox presents Horizon: What on Earth is wrong with Gravity? on BBC Two at 2100GMT, Tue 29 Feb or afterwards from BBC iPlayer. Posted by: Lucimary Vargas Além Paraíba-MG-Brasil observatorio.monoceros@gmail.com

Astrônomo investiga relação entre agricultura e as fases da lua

Professor Germano Afonso apresenta sua pesquisa na Coopavel com a ajuda de um planetário inflável

Lenara Londero | reportagem@canalrural.com.br

Quando estudamos a história das civilizações antigas na escola, aprendemos que naquele tempo em que os calendários ainda não haviam sido inventados os homens se guiavam pela posição dos astros para saber onde estavam e que estação climática estava próxima. Mas dificilmente reparamos como a astronomia, ciência que estuda a posição dos corpos celestes, pode ter relação com a agricultura. Este é o objetivo do pós-doutor em Astronomia pela Universidade de Paris, Germano Afonso.

Tendo como base uma estrutura inflável que reproduz o ambiente de um planetário, Afonso tem promovido sessões diárias de explicações sobre o papel da lua no campo para os agricultores que visitam o Show Rural Coopavel. O astrônomo, que há 16 anos estuda o conhecimento indígena brasileiro sobre os astros, quer montar um mapa do conhecimento de produtores sobre a relação entre as fases lunares e a agropecuária.

- O agricultor sabe que a melhor época pra podar a parreira é no início de agosto, quando a lua está minguante. Se você perguntar pra ele o motivo, ele vai dizer que não sabe, mas que o pai e o avô dele sempre fizeram assim, e é assim que dá certo. Estou buscando uma explicação científica para essa crença – exemplifica.
Após anos de pesquisas em etnoastronomia com índios, Germano agora quer investigar o conhecimento tradicional de agricultores ("os caboclos, aqueles que vivem na terra e da terra mesmo, os pequenos") sobre a ligação entre a lua e o sucesso da lavoura. O professor da Universidade Federal do Paraná acredita que a chave do mistério está na diferença de luminosidade proporcionada por cada fase do satélite da Terra.

- Os índios me ensinaram que o que influência não vem da atração gravitacional, que tem peso sobre as marés, mas sim da diferença de luz, porque quanto mais luz há, mais os insetos e pragas ficam ativos, agitados – logo, proporcionam maior prejuízo se o manejo da lavoura for feito em épocas de lua crescente ou cheia – explica.

Germano Afonso chama seu empreendimento de "resgate do conhecimento astronômico e sua aplicação na agricultura". Ele justifica seu interesse: se o Sol é indispensável para a agricultura, a Lua também tem papel fundamental .

- O conhecimento popular é muito desacreditado, mas há muita sabedoria no que o homem do campo diz e faz há décadas, séculos. O papel do cientista é resgatar esse conhecimento e sistematizá-lo, para que cada vez mais pessoas possam ser beneficiadas.

No meio da conversa que estávamos tendo ao lado de seu telescópio instalado em um estande da Coopavel, Germano se levantou, foi até um homem que estava passando pela feira, certificou-se de que ele era agricultor e perguntou: "O senhor acha que a lua tem alguma influência na hora de plantar, colher, podar?"

- Tem muitas plantas que cortamos na lua minguante. E tem plantas de raiz longa que, se plantar quando a lua é crescente, se desenvolvem pra cima da terra, ao invés de enterrar as raízes. Aí a planta fica fraca, então tem que plantar na minguante – respondeu o produtor de Ampére (PR) Antônio Pasqualotto, demonstrando estranheza pela pergunta, mas confirmando involuntariamente a teoria do professor Germano Afonso.

Atualmente o professor e pesquisador conta com apoio do Instituto Brasileiro de Assistência Social, Esportiva e Saúde (IBASS Corporate), uma organização da sociedade civil criada para administrar iniciativas voltados à educação, esporte, saúde, cultura, meio ambiente e projetos sociais. Ele revela que resolveu trazer o planetário móvel à Coopavel para disseminar sua pesquisa, estar em contato com os agricultores e também para atrair investidores interessados em financiar seu trabalho.

- Quero viajar por todas as regiões agrícolas do Paraná, conversar com os agricultores, aprender o que eles têm a dizer. Mas para isso preciso de recursos para deslocamento, alojamento, porque pesquisar também dá despesa. Pra chegar perto do conhecimento é preciso ouvir o agricultor de verdade, ir no lugar em que ele vive - explica.
CANAL RURAL

 

Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil
observatorio.monoceros@gmail.com

Stardust comet dust resembles asteroid materials

LIVERMORE, Calif. - Contrary to expectations for a small icy body, much of the comet dust returned by the Stardust mission formed very close to the young sun and was altered from the solar system's early materials.

When the Stardust mission returned to Earth with samples from the comet Wild 2 in 2006, scientists knew the material would provide new clues about the formation of our solar system, but they didn't know exactly how.

New research by scientists at Lawrence Livermore National Laboratory and collaborators reveals that, in addition to containing material that formed very close to the young sun, the dust from Wild 2 also is missing ingredients that would be expected in comet dust.  Surprisingly, the Wild 2 comet sample better resembles a meteorite from the asteroid belt rather than an ancient, unaltered comet.

Comets are expected to contain large amounts of the most primitive material in the solar system, a treasure trove of stardust from other stars and other ancient materials. But in the case of Wild 2, that simply is not the case.

By comparing the Stardust samples to cometary interplanetary dust particles (CP IDPs), the team found that two silicate materials normally found in cometary IDPs, together with other primitive materials including presolar stardust grains from other stars, have not been found in the abundances that might be expected in a Kuiper Belt comet like Wild 2. The high-speed capture of the Stardust particles may be partly responsible; but extra refractory components that formed in the inner solar nebula within a few astronomical units of the sun, indicate that the Stardust material resembles chondritic meteorites from the asteroid belt.

"The material is a lot less primitive and more altered than materials we have gathered through high altitude capture in our own stratosphere from a variety of comets," said LLNL's Hope Ishii, lead author of the research that appears in the Jan. 25 edition of the journal, Science. "As a whole, the samples look more asteroidal than cometary."

Because of its tail formed by vaporizing ices, Wild 2 is, by definition, a comet. "It's a reminder that we can't make black and white distinctions between asteroids and comets," Ishii said. "There is a continuum between them."

The surprising findings contradict researchers' initial expectations for a comet that spent most of its life orbiting in the Kuiper Belt, beyond Neptune. In 1974, Wild 2 had a close encounter with Jupiter that placed it into its current orbit much closer to Earth.

Comets formed beyond the so-called frost line where water and other volatiles existed as ices. Because of their setting far from the sun, they have been viewed as a virtual freezer, preserving the original preliminary ingredients of the solar system's formation 4.6 billion years ago. The Stardust spacecraft traveled a total of seven years to reach Wild 2 and returned to Earth in January 2006 with a cargo of tiny particles for scientist to analyze.

This is one of the first studies to closely compare Stardust particles to CP IDPs. This class of IDPs is believed to contain the most primitive and unaltered fraction of the primordial material from which our planets and other solar system objects formed. They are highly enriched in isotopically anomalous organic and inorganic outer solar nebula materials inherited - through the presolar molecular cloud - from dust produced around other stars. IDPs are gathered in the stratosphere by high altitude airplanes (ER-2s and WB-57s) that are typically more than 50 years old.

The Livermore team specifically searched for two silicate materials in Stardust that are believed to be unique to cometary IDPs: amorphous silicates known as GEMS (glass with embedded metal and sulfides); and sliver-like whiskers of the crystalline silicate enstatite (a rock-forming mineral). Surprisingly, the team found only a single enstatite whisker in the Stardust samples, and it had the wrong crystallographic orientation - a form typical of terrestrial and asteroidal enstatite.

Objects similar to GEMS were found, but Ishii and the team showed they were actually created during the high speed 6-kilometer per second impact of Wild 2 comet dust with the Stardust spacecraft's collector by making similar material in the laboratory.

In analyzing the Stardust material, Ishii's team used Livermore's SuperSTEM (scanning transmission electron microscope). Ishii said future analyses should focus on larger-grained materials, so-called micro-rocks, which suffered less alteration.

"The material found in primitive objects just wasn't there in the samples," said John Bradley, another LLNL author. "I think this is science in action. It's really exciting because it's just not what we expected."

"Wild 2 doesn't look like what we thought all comets should look like," Ishii said. "The Stardust mission was a real success because without it, we would never have learned these things about our solar system. The sample return was vital for us to continue to unravel how our solar system formed and evolved."

In addition to Ishii and Bradley, other LLNL researchers include Zu Rong Dai, Miaofang Chi and Nigel Browning. Other institutions involved include UC Davis, the Natural History Museum of London, the University of Kent and the Netherlands Organization for Scientific Research (NWO).

Stardust is a part of NASA's series of Discovery missions and is managed by the Jet Propulsion Laboratory. Stardust launched in February 1999 and set off on three giant loops around the sun. It began collecting interstellar dust in 2000 and met Wild 2 in January 2004, when the spacecraft was slammed by thousands of comet particles including some the size of BBs that could have compromised the mission. It is the first spacecraft to safely make it back to Earth with cometary dust particles in tow.

Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by Lawrence Livermore National Security, LLC for the U.S. Department of Energy's National Nuclear Security Administration.

Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil
observatorio.monoceros@gmail.com

A theory of everything

Astronomers propose an astronomical test of string theory.

Provided by the U of I at Urbana-Champaign

This image shows the how the Big Bang formed our universe. Astronomy: Roen Kelly [View Larger Image] January 30, 2008 Ancient light absorbed by neutral hydrogen atoms could be used to test certain predictions of string theory, say cosmologists at the University of Illinois. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the Moon. String theory, a theory whose fundamental building blocks are tiny one-dimensional filaments called strings, is the leading contender for a "theory of everything." Such a theory would unify all four fundamental forces of nature (the strong and weak nuclear forces, electromagnetism, and gravity). But finding ways to test string theory has been difficult. Now, cosmologists at the U of I say absorption features in the 21-centimeter spectrum of neutral hydrogen atoms could be used for such a test. "High-redshift, 21-centimeter observations provide a rare observational window in which to test string theory, constrain its parameters and show whether or not it makes sense to embed a type of inflation, called brane inflation, into string theory," says Benjamin Wandelt, a professor of physics and of astronomy at the U of I. "If we embed brane inflation into string theory, a network of cosmic strings is predicted to form," Wandelt says. "We can test this prediction by looking for the impact this cosmic string network would have on the density of neutral hydrogen in the universe." About 400,000 years after the Big Bang, the universe consisted of a thick shell of neutral hydrogen atoms (each composed of a single proton orbited by a single electron) illuminated by what became known as the cosmic microwave background. Because neutral hydrogen atoms readily absorb electromagnetic radiation with a wavelength of 21 centimeters, the cosmic microwave background carries a signature of density perturbations in the hydrogen shell, which should be observable today, Wandelt says. Cosmic strings are filaments of infinite length. Their composition can be loosely compared to the boundaries of ice crystals in frozen water. When water in a bowl begins to freeze, ice crystals will grow at different points in the bowl, with random orientations. When the ice crystals meet, they usually will not be aligned to one another. The boundary between two such misaligned crystals is called a discontinuity or a defect. Cosmic strings are defects in space. A network of strings is predicted by string theory (and also by other supersymmetric theories known as Grand Unified Theories, which aspire to unify all known forces of nature except gravity) to have been produced in the early universe, but has not been detected so far. Cosmic strings produce characteristic fluctuations in the gas density through which they move, a signature of which will be imprinted on the 21-centimeter radiation. The cosmic string network predicted to occur with brane inflation could be tested by looking for the corresponding fluctuations in the 21-centimeter radiation. Like the cosmic microwave background, the cosmological 21-centimeter radiation has been stretched as the universe has expanded. Today, this relic radiation has a wavelength closer to 21 meters, putting it in the long-wavelength radio portion of the electromagnetic spectrum. To precisely measure perturbations in the spectra would require an array of radio telescopes with a collective area of more than 1,000 square kilometers. Such an array could be built using current technology, Wandelt says, but would be prohibitively expensive. If such an enormous array were eventually constructed, measurements of perturbations in the density of neutral hydrogen atoms could also reveal the value of string tension, a fundamental parameter in string theory, Wandelt says. "And that would tell us about the energy scale at which quantum gravity begins to become important."

 

 

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Lucimary Vargas
Além Paraíba-MG-Brasil
observatorio.monoceros@gmail.com

Old galaxies discovered

Astronomers uncover ancestors of Milky Way-type galaxies.

Provided by Rutgers University

Galaxy M74 is representative of spiral galaxies that evolved from recently discovered galaxies in the early universe. odd Boroson/NOAO/AURA/NSF [View Larger Image] January 25, 2008 Astronomers at Rutgers and Penn State universities have discovered galaxies in the distant universe that are ancestors of spiral galaxies like our Milky Way. These ancient objects, some of the first galaxies ever to form, are being observed as they looked when the universe was a mere 2 billion years old. Today, scientists peg the universe's age at 13.7 billion years, so light from these galaxies traveled almost 12 billion years to reach Earth. The newly discovered galaxies are quite small, one-tenth the size and one-twentieth the mass of our Milky Way. They also have fewer stars, only one-fortieth as many as are in the Milky Way. From ground-based telescopes, they look like individual stars in size. Recent images made by the Hubble Space Telescope, however, reveal them as regions of active star formation. "Finding these objects and discovering that they are a step in the evolution of our galaxy is akin to finding a key fossil in the path of human evolution," says Eric Gawiser, assistant professor in the Department of Physics and Astronomy in the Rutgers School of Arts and Sciences.

This image shows an extended, chain-like Lyman alpha emitter. NASA/ESA/C. Gronwall/Penn State [View Larger Image] The researchers determined that these galaxies were fertile breeding grounds for new stars, which burned hot and bright. These stars ionized the hydrogen atoms around them, stripping them of their electrons and causing them to emit a tell-tale sharp band of ultraviolet light known as Lyman alpha. The researchers also noted that several of these galaxies, sometimes 10 or more, pulled together over the ensuing few billion years to form a single spiral galaxy. "The Hubble Space Telescope has delivered striking images of these early galaxies, with 10 times the resolution of ground-based telescopes," says Caryl Gronwall, senior research associate in Penn State's Department of Astronomy & Astrophysics. "They come in a variety of shapes, round, oblong, and even somewhat linear, and we are starting to make precise measurements of their sizes." The astronomers discovered these galaxies as part of a 5-year-old census of galaxies in the early universe, a project called MUSYC (Multi-Wavelength Survey by Yale and Chile). Gawiser, while a National Science Foundation (NSF) astronomy and astrophysics postdoctoral fellow at Yale, initiated a search for several types of galaxies that could be precursors of Milky Way-type spirals; Gronwall led an investigation into the luminosity, density and distribution of the distinctive Lyman alpha emitters. Their statistical analyses and computer simulations of how galaxies cluster led them to the conclusion they first reported in December 2007: Lyman alpha emitters are the ancestors of spiral galaxies.

This image shows an extended Lyman alpha emitter which shows evidence of merging. NASA/ESA/C. Gronwall/Penn State [View Larger Image] "We knew by our understanding of cosmological theory that spiral galaxies had to evolve from low-mass galaxies such as these," Gawiser says. "The challenge was to actually find them. We'd seen other early universe galaxies, but they were bigger and destined to evolve into elliptical galaxies, not spirals." The astronomers undertook four types of observations to find and characterize the objects they were seeking. They performed the first step, actually finding the Lyman alpha-emitting galaxies amid all the visible objects of deep space, using the Blanco 4-meter telescope at the NSF Cerro Tololo Inter-American Observatory in Chile. To measure their distance, they used the Magellan Telescope at Las Campanas Observatory, also in Chile, to measure redshift, an effect that shows how fast an object is receding from view due to a rapidly expanding universe. (The redshift at which they studied these galaxies is 3.1.) To determine how many stars are in the galaxies, they used the NASA Spitzer Space Telescope's Infrared Array Camera. And to determine how big the galaxies are, they used the NASA Hubble Space Telescope's Advanced Camera for Surveys. "Astronomy has long used a model where big surveys are followed by detailed studies of the interesting objects they find," says Nigel Sharp, program officer in NSF's Division of Astronomical Sciences. "This work nicely couples the large area, wide-field view of our ground-based telescope with the sharp focus of the Hubble, to probe to the faintest light levels. This team has come the closest yet to finding young galaxies that resemble our own Milky Way in its infancy."

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Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil
observatorio.monoceros@gmail.com

Cosmic fireworks fizzled out at universe's mid-life

UNIVERSITY OF TEXAS-AUSTIN NEWS RELEASE
Posted: January 25, 2008

AUSTIN, Texas ‹ We all start to party less around middle age, and new studies by a team led by University of Texas at Austin astronomer Shardha Jogee now finds that the universe, as a whole, is no exception.

According to the current models of galaxy formation, dubbed "hierarchical lambda cold dark matter" models, galaxies built up to their current masses, shapes, and sizes through the successive mergers of less massive protogalaxies made of gas, stars, and dark matter. In the first quarter of the universe's lifespan, the cosmic landscape was dominated by violent galaxy mergers, which could radically transform the shape of a galaxy and convert its gas into stars at an extreme rate. More than half of bright galaxies were indulging in such violent "partying."

New research is showing that all changed when the universe hit middle age. "Our study finds that over the last 7 billion years, after the universe hit its mid-forties, so to speak, it transitioned from a violent merger-driven mode into a quieter mode," Jogee said.

She and her team find that over each billion-year interval, only 10% of galaxies are typically involved in strong interactions and mergers.

Jogee's research team includes University of Texas at Austin students Sarah Miller and Kyle Penner, as well as her colleagues in the international GEMS collaboration, whose principal investigator is Hans-Walter Rix of the Max Planck Institute for Astronomy. Jogee's team has analyzed more than 5,000 galaxies imaged by Hubble Space Telescope as part of GEMS, one of the largest-area surveys conducted with Hubble in two filters.

"With Hubble's spectacular resolution," Penner said, "we could discern amazing tell-tale clues of the mergers and interactions ‹ huge tails, warps, ripples, double nuclei ‹ in galaxies billions of light-years away."

"It's been exciting to apply different complementary techniques in this large survey," Miller said, "and to sift through the merger history of the universe during this elusive era." Miller is the recipient of a 2008 Rhodes scholarship from Oxford University.

In addition to estimating the frequency of mergers, Jogee and her colleagues found that contrary to what is commonly assumed, the average star formation rate in these interacting and merging galaxies is only enhanced by a modest factor of two to three compared to that in normal non-interacting galaxies.

"While extreme bursts of star formation, so-called cosmic fireworks, may happen in some galaxy mergers or interactions, they are not the norm in the vast majority of galaxy interactions taking place over the last 7 billion years," Jogee said.

The findings of Jogee's team result from a powerful synergy of data from NASA's Hubble and Spitzer space telescopes. "Mid-infrared observations from the Spitzer Space Telescope, taken by George Rieke of The University of Arizona, were key for tracing hidden star formation, obscured by dust," Jogee said. "The exquisite resolution of the GEMS Hubble data in turn allowed us to identify strongly interacting and merging galaxies at much earlier cosmological times than conventional ground-based telescopes," said team member Daniel McIntosh of the University of Massachusetts, Amherst.

Jogee and her team, in fact, find that only 20% of the total cosmic star formation that took place over the last 7 billion years appears to come from strongly interacting and merging galaxies. These results extend the similar trend found for a smaller sample of about 1,500 galaxies over a narrower time interval by fellow team members Christian Wolf from Oxford University and Eric Bell of the Max Planck Institute of Astronomy.

Furthermore, the results reported by Jogee and her team on the modest fraction (about 20%) of merger-induced star formation, and the frequency of galaxy mergers over the last 7 billion years, are in remarkably good agreement with prevailing theoretical cold dark matter models of galaxy evolution.

According to team member Rachel Somerville of the Max Planck Institute of Astronomy, "Mergers are thought to be a crucial process in transforming galaxies, causing bursts of star formation, and perhaps even feeding gas to the supermassive black holes lurking in the galaxy's nucleus.

"Although the frequency of mergers predicted by the models agrees quite well with the observed frequency," Somerville said, "these observations can also teach us much more about the effect these violent episodes have on galaxies."

In fact, Jogee said, "Our results raise many additional questions which can only be addressed with next generation facilities. For example, the cosmic star-formation rate is declining in normal galaxies, but it remains unclear what drives this decline. Are galaxies using up their internal cold gas supply, or is the accretion rate of gas from external filaments declining?"

Next-generation radio facilities, such as ALMA [the Atacama Large Millimeter/Sub-millimeter Array] will be critical for exploring how the cold gas content of galaxies changes over the last seven billion years, she said.

"Another key thing to note is that some of our results starkly disagree with prevailing hierarchical models of galaxy evolution," Jogee said. According to these models, the frequency of pure disk galaxies or so-called "bulgeless galaxies" is expected to be extremely low, because a past major merger in the life of every galaxy invariably builds a bulge.

Contrary to such predictions, postdoctoral fellow Fabio Barazza, formerly working with Jogee at The University of Texas and now at Geneva Observatory's Ecole Polytechnique Federale de Lausanne, found that about 20% of present-day spiral galaxies are bulgeless or disk-dominated, based on the analysis of about 1,000 galaxies from the Sloan Digital Sky Survey.

"We also see striking super-thin bulgeless galaxies in GEMS, at earlier epochs," Jogee said. "We yet have to characterize the frequency and origin of these enigmatic bulgeless galaxies at different epochs, but there is no denying their prevalence in the local universe."

All in all, "We have made important headway in piecing part of the cosmic puzzle of galaxy evolution, but daunting challenges loom ahead for both observers and theorists," she said.

 

Posted by:
Lucimary Vargas
Além Paraíba-MG-Brasil
observatorio.monoceros@gmail.com