Science News

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Mission controllers cross their fingers whenever the Sun is stormy and their spacecraft have to fly over the South Atlantic. There, even satellites in low orbits suffer many hits by atomic bullets from the Sun. http://www.hypography.com/gallery/files/5/earth_magnetic_400_thumb.jpgTroublesome faults occur in electronic systems and astronauts see flashes in their eyes. The Earth's magnetic field, which shields our planet against charged atomic particles coming from outer space, is curiously weak in that region. The South Atlantic Anomaly, as the experts call it, is one pressing reason why they are intensifying their exploration of the Earth's magnetism. Denmark's Ørsted satellite, launched in 1999, is dedicated to magnetic research, whilst Germany's CHAMP mission (2000) measures both magnetism and gravity. These satellites show that the danger zone for satellites over Brazil and the South Atlantic is growing wider towards the southern Indian Ocean. The Earth's magnetic field is becoming generally weaker at an astonishing rate. When a French-Danish team compared Ørsted's results for 2000 with those from an American satellite, Magsat, 20 years earlier, the decline in the field's strength suggested that it might disappear completely in a thousand years or so. The experts wonder if our planet is preparing to swap its north and south magnetic poles around, as it has often done before during the Earth's long history. These and other mysteries about our magnetic planet will get the closer attention they deserve, in ESA's forthcoming Swarm project. Three satellites will work together to measure the magnetic field and its variations far more accurately than ever before. The Swarm mission was proposed to ESA by Eigil Friis-Christensen (Copenhagen), Hermann Lühr (Potsdam) and Gauthier Hulot (Paris) with support from scientists in seven European countries and the USA. ESA selected the project in 2004 as an 'opportunity mission' in its Earth Explorer programme. All being well, Swarm will be operational by 2009. After climbing into space on a single launcher, the satellites will adopt orbits passing over the Earth's poles. Swarm A and B will fly side by side, simultaneously measuring the magnetic field from positions up to 150 kilometres apart in the east-west direction near the equator. Their orbits will at first be 450 kilometres above the surface, but by the end of the mission they will come as low as 300 kilometres, for more accurate measurements of magnetism originating from the Earth's crust. Swarm C will always fly higher, remaining at more than 500 kilometres altitude throughout the mission. Compared with its sisters, Swarm C will give simultaneous snapshots of the magnetic field over quite different regions of the Earth, and impressions of the same region at different times of day. Separating the different sources of magnetism Ordinary magnetic compasses obey the main magnetic field, produced by electric currents in the Earth's core of molten iron. But in magnetic storms, compass needles wander. Since the 19th Century scientists have linked these storms to eruptions on the Sun. Many space ventures, recently including the ESA-NASA SOHO spacecraft and ESA's four-satellite Cluster mission, have helped to clarify the solar connection. We live in a protective bubble in space called the magnetosphere. At its boundary, gusts in a non-stop solar wind of atomic particles battle with the Earth's magnetism. As a result, events in outer space make a continual but highly variable contribution to the magnetic field. So do electric currents in the ionosphere, the zone of free electrons and charged air molecules high in the atmosphere that's best known for reflecting radio signals. Other, much weaker patterns are overlaid on the global picture. In the Earth's crust, many rocks have built-in magnetism that remembers the direction of the main magnetic field when they formed. This affects the field measured locally. By its subtle east-west comparisons Swarm will picture the magnetic field of the crust with unprecedented clarity. And even ocean water generates electric currents as it move in the main field, so that the ebb and flow of the tides have a slight magnetic effect. As gauged by the satellites, the main field is roughly 6,000 times stronger than the rock magnetism of the ocean floor, and 30,000 times greater than the influence of the oceanic tides. Only with delicate measurements by satellite constellations, supported by ground stations, ships and aircraft carrying magnetic instruments, can scientists sort out all the patterns of magnetism from the different sources. The most careful analyses reveal yet another effect. Magnetic variations drive electric currents in the mantle, the main region between the core and the crust. These in turn cause further magnetic changes, from which scientists can estimate the electrical conductivity of the mantle. This provides a check on the temperature of the material hidden deep in the Earth's interior. "What excites us is the huge scope of what we can study even with quite small satellites," comments Nils Olsen of the Danish National Space Center in Copenhagen, who analyses Ørsted's results while he helps to plan Swarm. "By making magnetic measurements in space we get new information about the Earth, from the molten core deep under our feet, through the mantle, to the crust on which we live. And then we go on upwards into the upper atmosphere, through the planet's local space environment, and all the way to the Sun itself, which is the source of daily magnetic disturbances." Practical benefits Solar storms can be fatal for satellites, and not only on account of radiation damage. The atmosphere inflates and low-orbiting spacecraft run into unexpected air resistance. Experts used to think it was just a matter of the air being heated by particles and electric currents in the regions around the poles, where auroras occur. Now a sensitive French-built accelerometer on the German CHAMP satellite has revealed heating by intense currents where the solar wind pushes towards the magnetic poles in daytime. The three Swarm satellites will investigate this new effect with accelerometers of their own. Swarm's operational lifetime, 2009-13, will coincide with the next expected peak of storminess on the Sun. Immediate practical benefits will centre on Swarm's general monitoring of space weather, and the solar events affecting not just spacecraft and astronauts but technological systems on the ground as well. Magnetic storms can damage power systems and pipelines, whilst the changes in the magnetic field can mislead any navigational systems that use magnetic compasses. These include compasses operating underground to guide the drills used to find and recover oil. For scientists, the biggest benefit of Swarm is that high-quality magnetic measurements provide a new way of 'x-raying' the hidden interior of planet. Earthquake waves and variations in the strength of gravity already provide a picture of the hot core, the rocky mantle that surrounds it, and the ever-active crust. But the picture is not yet clear enough for scientists to agree how the internal machinery of the planet really works. "Magnetic measurements give a fresh point of view on the Earth's interior," says Roger Haagmans, who is responsible for solid-Earth science in ESA's Earth Observation programme. "And Swarm will also investigate the puzzling changes in the Earth's core that are responsible for the present weakening of the magnetic field. That's already a matter of practical concern for many satellite operators. With a better idea of the reasons, we may know what to expect in the busy decades of spaceflight that we have ahead of us." Source: European Space Agency

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The center of our galaxy is hidden behind a "brick wall" of obscuring dust so thick that not even the Hubble Space Telescope can penetrate it. Astronomers Silas Laycock and Josh Grindlay (Harvard-Smithsonian Center for Astrophysics) and colleagues have lifted that veil to reveal a beautiful vista swarming with stars. http://www.hypography.com/gallery/files/5/upper_right_color_lores_thumb.jpgMoreover, their hunt for specific stars associated with X-ray-emitting sources has ruled out one of two options for the nature of these X-ray sources: most apparently are not associated with massive stars, which would have shown up as bright counterparts in their deep infrared images. This points to the X-ray sources being white dwarfs, not black holes or neutron stars, accreting matter from low-mass binary companion stars. Their study is being presented today at a press conference at the 205th meeting of the American Astronomical Society in San Diego, Calif. To peer into the galactic center, Laycock and Grindlay used the unique capabilities of the 6.5-meter-diameter Magellan Telescope in Chile. By gathering infrared light that more easily penetrates dust, the astronomers were able to detect thousands of stars that otherwise would have remained hidden. Their goal was to identify stars that orbit, and feed, X-ray-emitting white dwarfs, neutron stars or black holes - any of which could yield the faint X-ray sources discovered originally with NASA's Chandra X-ray Observatory. Chandra previously detected more than 2000 X-ray sources in the central 75 light-years of our galaxy. About four-fifths of the sources emitted mostly hard (high-energy) X-rays. The precise nature of those hard X-ray sources remained a mystery. Two possibilities were suggested by astronomers: 1) high-mass X-ray binary systems, containing a neutron star or black hole with a massive stellar companion; or, 2) cataclysmic variables, containing a highly magnetized white dwarf with a low-mass stellar companion. Determining the nature of the sources can teach us about the star formation history and dynamical evolution of the region near the galactic center. "If we found that most of the hard X-ray sources were high-mass X-ray binaries, it would tell us that there had been a lot of recent star formation because massive stars don't live long," says Laycock. "Instead, we found that most of the X-ray sources are likely to be older systems associated with low-mass stars." That conclusion comes from a null result: that is, most of the counterparts to the X-ray sources must be fainter than the brightness expected if the X-ray sources had massive companions. Since massive stars are both rare and bright, an association with the X-ray sources would have been easy to spot. Smaller stars are more common and fainter, making it difficult to match them to a specific X-ray source. Analysis of the infrared images found only a chance number of matches between stars and the locations of X-ray sources. Many of those matches likely were due to the crowded field of view. "The fact that we found no significant excess of bright infrared counterparts means that the galactic center Chandra sources are probably low-mass binaries. Since by far the most common low-mass binaries with X-ray luminosities, spectra, and variability similar to the galactic center Chandra sources are accreting magnetic white dwarfs, we conclude these are the most likely identification," says Grindlay. If the X-ray sources near the galactic center are accreting white dwarfs, the large numbers of compact low-mass binaries required could suggest that they formed in the very dense star cluster around the galactic center or that they have been "deposited" there by the destruction of globular clusters. Deeper infrared observations and spectra of the sources are needed to make actual identifications and constrain the masses of the accreting compact objects. Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe. Source: Harvard-Smithsonian Center for Astrophysics

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Wouldn't it be convenient if your birthday, Christmas and the Fourth of July -- not to mention most other major holidays -- all fell on the same day of the week, year after year? Wouldn't it make life -- or at least planning -- easier, for instance, to know that Dec. 17 would always fall on a Saturday or that January 1 -- New Year's Day -- would always be celebrated on a Sunday? Richard Conn Henry, professor in the Henry A. Rowland Department of Physics and Astronomy at The Johns Hopkins University, thinks it would. He has designed -- using computer programs and complex mathematical formulas -- a new calendar that would make it happen. Under Henry's plan, each new 12-month period is identical to the one that came before. Each month has either 30 or 31 days. January, for instance, would have 30 days, as would February, April, May, July, August, October and November. March, June, September and December would all have 31 days. Henry, a physicist who also directs the Maryland Space Grant Consortium, says his new calendar would have "profound economic and practical benefits" if adopted worldwide. He is waging a Web-based campaign to make this happen by Jan. 1, 2006. Henry points out that this transition date is ideal, because New Year's Day 2006 falls on a Sunday on both the old and proposed calendars, facilitating a seamless transition. "Just ask yourself how much time and effort are expended each year in redesigning the calendar of every single organization worldwide to accommodate the coming year's calendar, and it becomes obvious that my calendar would make life much simpler and would have noteworthy benefits economically, especially for businesses and other institutions," Henry said. "With my plan, we can have a stable calendar that is absolutely identical from year to year and which allows the permanent, rational planning of annual activities, from school to work holidays." Called the "Calendar-and-Time Plan" (C&T) because it also advocates the worldwide adoption of a 24-hour, universal time scale (more on that later), Henry's innovation promises to improve on what he sees as the "defects" of the dozen or so rival reform calendars that have been proffered by various individuals and institutions in the past 100 years. "Calendar reform has always failed before, and for a simple reason: All major proposals involved breaking the seven-day cycle of the week, which has always been -- and probably will always be -- completely unacceptable to humankind because it goes against the Fourth Commandment of the Bible about keeping the Sabbath Day," Henry said. "C&T never breaks that biblical cycle." What's more, the C&T calendar is "far more convenient" than is the current Gregorian calendar, which has been in place for more than 400 years -- ever since Pope Gregory, in 1582, modified a calendar that was instituted by Julius Caesar in 46 BC. To bring Caesar's calendar into sync with the seasons (one of the main reasons for reforming it), the pope and his scholars removed 11 days from the calendar during that October, so that Oct. 4 was followed immediately by Oct. 15. The need for that kind of adjustment derived from the same problem that makes designing an effective calendar a challenge today: the fact that there is an uneven number of days in an Earth year: 365.2422 days, to be exact. Our current calendar tackles this challenge by instituting "leap years" every four years. Henry thinks he has found a better solution: drop leap year entirely and institute, instead, a one-week "mini-month" between June and July every five or six years. In honor of his personal hero, Sir Isaac Newton, Henry has dubbed this seven-day period "Newton." His computer calculation ensures that "Newton Week" brings the new calendar in sync with seasonal changes as the Earth circles the sun. Newton Weeks would bring with them benefits not enjoyed under the Gregorian calendar, Henry said. "If I had my way, everyone would get Newton Week off as a paid vacation and could spend the time doing physics, or other activities of their choice," he said, only half jokingly . "You can't say the same of leap years." Newton Week would pop up irregularly: 2009, 2015, 2020 and 2026, for instance, would all need a Newton Week to keep the calendar as close to the cycle of the seasons as possible. As a result, the new calendar is never more than five days off the seasons. In fact, after Jan.1, 2006, the C&T calendar would be identical to the current calendar 15 percent of the time, and only one day different 29 percent of the time. Henry has established what he calls the "International Association for 2006," an online organization aimed at rallying support for his plan. He serves as president of the organization, and Jess Cully, a calendar reform enthusiast from Portsmouth, England, is now vice president for that country. In addition to advocating the adoption of the new calendar, Henry also urges everyone to simultaneously switch to what is called "Universal Time" (formerly known as Greenwich Mean Time). Doing so would synchronize the date and time the same worldwide, streamlining such things as international business and exchange. "We would quickly get used to the fact that sunrise and sunset henceforth occur at what seem to us unusual hours by the clock," Henry said. "My late mother, for example, successfully switched from Fahrenheit temperature to Celsius, telling me on one occasion, 'It's a very hot day -- 30 degrees!' That shows me that people are adaptable if benefits are there. The C&T benefit is much greater than that resulting from the change from Fahrenheit to Celsius." Source: Johns Hopkins University

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An ancient mystery may have been solved by LSU Associate Professor of Physics and Astronomy Bradley E. Schaefer. http://www.hypography.com/gallery/files/5/farneseback_thumb.jpg Schaefer has discovered that the long-lost star catalog of Hipparchus, which dates back to 129 B.C., appears on a Roman statue called the Farnese Atlas. Hipparchus was one of the greatest astronomers of antiquity and his star catalog was the first in the world, as well as the most influential. The catalog was lost early in the Christian era, perhaps in the fire at the great library in Alexandria. The Farnese Atlas is a Roman statue, dating to the second century, that depicts the Titan Atlas holding a sky globe on his shoulder. The statue, currently housed in Italy, includes relief figures on the globe depicting the ancient Greek constellations in fine detail. Schaefer has discovered that the constellation figures on the Farnese Atlas are an accurate rendition of Hipparchus' star catalog. According to Schaefer, the discovery will likely lead to the solution of several long-debated questions. Indeed, Schaefer's discovery is already stirring interest among those in the field of astronomy. "The constellations are one of our more enduring intellectual properties, and in antiquity, they turned the night sky into familiar territory. Dr. Schaefer's clever and disciplined analysis of the oldest graphic representation of the traditional Greek constellations reveals unexpected roots of scientific astronomy in a celebrated work of ancient art," said E.C. Krupp, director of the Griffith Observatory in Los Angeles. Schaefer, who earned his doctorate from the Massachusetts Institute of Technology in 1983, specializes in astronomy and astrophysics. He has long been interested in the history of astronomy and has written extensively on the subject. He began his examination of the Farnese Atlas statue while conducting research on ancient constellation lore. Schaefer said that scientists have long held Hipparchus in high regard for his work, which was conducted between 140 B.C. and 125 B.C. He is known for the discovery of the first nova and a process called precession; a theory for the motions of the sun and moon; top-quality planetary observations; and the first-ever catalog of about 1,000 stars. Unfortunately, only one of Hipparchus' books has survived to today: "Commentaries," which describes the constellation figures in detail. The rest of his written work is known only through the references of later astronomers. For example, Schaefer said, Hipparchus' star catalog was described in the work "Almagest" by the influential Greek astronomer and geographer Ptolemy, who lived around A.D. 85 to A.D. 165. The Farnese Atlas – roughly seven feet tall and made of marble – is now in the Farnese Collection in the National Archaeological Museum in Naples, Italy. The statue's sky globe, which is 26 inches in diameter, shows 41 Greek constellations, as well as the celestial equator, tropics and ecliptic. Art historians have concluded that the statue is a late Roman copy of a Greek original. Schaefer said that the constellations are accurately depicted, so the sculptor must have based his work on some specific astronomical observations. Throughout the last century, Schaefer explained, these observations have been attributed to many sources, but not Hipparchus. Schaefer said that a number of facts led to the conclusion that the statue's sky globe was based on Hipparchus' catalog. Precession, as discovered by Hipparchus, is a process whereby the stars and constellation figures slowly move with respect to the celestial equator, tropics and lines of constant right ascension. This provides the key to dating the original observations, Schaefer explained, because it means that investigators need only look on the sky globe to see what date matches the constellation positions. Thus, Schaefer traveled to Naples and made the first astronomical analysis of the constellation positions. For his analysis, Schaefer took his own pictures, because the photographic analysis requires knowledge of the distance between globe and camera. He measured a total of 70 positions on the globe and made a formal mathematical fit to find the best date. Schaefer concluded that the best date for the original observations is 125 B.C. He said that the normal margin of error in this result is ±55 years. In other words, Schaefer said, there is a two-thirds chance that the real date was somewhere between 180 B.C. and 70 B.C. Schaefer said that the date of 125 B.C. immediately points to Hipparchus' circa-129 B.C. catalog as the original observational source. Indeed, he said, all previously proposed source candidates are confidently eliminated because they come from time periods that are either too early or too late. Positioning on the globe is another key indicator of the source, said Schaefer. The positioning of the constellation figures on the Farnese Atlas has a typical accuracy of 3.5 degrees. Schaefer said that such accuracy is essentially impossible to achieve by simple verbal descriptions (as found in the works of other potential sources, such as Aratus or Eudoxus) which are accurate to around 8 degrees. Nevertheless, ancient star catalogs would have the required accuracy. However, it is Hipparchus who is known to have a star catalog created around the correct time, 129 B.C., whereas the next catalog, created by Ptolemy, came much too late, in A.D. 128. In addition, Schaefer said it is known that Hipparchus constructed many sky globes based on his star catalog. For instance, ancient coins depict Hipparchus seated in front of a globe and Ptolemy writes explicitly of Hipparchus making such globes. Thus, Schaefer explained, a likely scenario is that Hipparchus used his catalog to make an accurate globe, which was later copied exactly by a Greek statue sculptor. Then, the Greek statue was later copied by a Roman sculptor. The constellations of the Farnese Atlas also contain many specific details that point to Hipparchus as the original observer. Schaefer made a comparison between the Farnese Atlas and all ancient constellation descriptions, including those of Ptolemy and other ancient astronomers and thinkers, such as Hipparchus, Aratus, Eratosthenes, Eudoxus and Homer. All ancient sources other than Hipparchus have many and major differences in their descriptions of the constellations. However, the detailed comparison shows Hipparchus' "Commentary" to have no differences and many unique similarities. Thus, the case for Hipparchus' lost star catalog appearing on the Farnese Atlas is based on: The derived date of 125 B.C., which matches Hipparchus and rejects all other candidates; The fact that the accuracy of the sky globe requires a star catalog, and only Hipparchus had created one before A.D. 128; The fact that Hipparchus is known to have produced working sky globes from his catalog; The fact that only Hipparchus' description of the constellation figures matches the Farnese Atlas. Schaefer said that the discovery of Hipparchus' lost star catalog on the Farnese Atlas could provide answers to two long-standing questions that have been the source of heated debate: What did Hipparchus use as coordinates and what fraction of Hipparchus' star catalog made it into Ptolemy's "Almagest?" Now, Schaefer said, with an accurate representation of Hipparchus' catalog, researchers can make exhaustive correlations between all constellation figures on the Farnese Atlas and those contained within "Almagest." But, Schaefer said, perhaps the best part of the discovery is "simply that we have recovered one of the most famous known examples of lost ancient wisdom." Source: Louisiana State University

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http://www.hypography.com/gallery/files/5/huygens005_thumb.jpgToday, after its seven-year journey through the Solar System on board the Cassini spacecraft, ESA’s Huygens probe has successfully descended through the atmosphere of Titan, Saturn’s largest moon, and safely landed on its surface. The first scientific data arrived at the European Space Operations Centre (ESOC) in Darmstadt, Germany, this afternoon at 17:19 CET. Huygens is mankind’s first successful attempt to land a probe on another world in the outer Solar System. “This is a great achievement for Europe and its US partners in this ambitious international endeavour to explore the Saturnian system,” said Jean-Jacques Dordain, ESA’s Director General. Following its release from the Cassini mothership on 25 December, Huygens reached Titan’s outer atmosphere after 20 days and a 4 million km cruise. The probe started its descent through Titan’s hazy cloud layers from an altitude of about 1270 km at 11:13 CET. During the following three minutes Huygens had to decelerate from 18 000 to 1400 km per hour. A sequence of parachutes then slowed it down to less than 300 km per hour. At a height of about 160 km the probe’s scientific instruments were exposed to Titan’s atmosphere. At about 120 km, the main parachute was replaced by a smaller one to complete the descent, with an expected touchdown at 13:34 CET. Preliminary data indicate that the probe landed safely, likely on a solid surface. The probe began transmitting data to Cassini four minutes into its descent and continued to transmit data after landing at least as long as Cassini was above Titan’s horizon. The certainty that Huygens was alive came already at 11:25 CET today, when the Green Bank radio telescope in West Virginia, USA, picked up a faint but unmistakable radio signal from the probe. Radio telescopes on Earth continued to receive this signal well past the expected lifetime of Huygens. Huygens data, relayed by Cassini, were picked up by NASA’s Deep Space Network and delivered immediately to ESA’s European Space Operation Centre in Darmstadt, Germany, where the scientific analysis is currently taking place. “Titan was always the target in the Saturn system where the need for ‘ground truth’ from a probe was critical. It is a fascinating world and we are now eagerly awaiting the scientific results,” says Professor David Southwood, Director of ESA’s scientific programmme. “The Huygens scientists are all delighted. This was worth the long wait,” says Dr Jean-Pierre Lebreton, ESA Huygens Mission Manager. Huygens is expected to provide the first direct and detailed sampling of Titan’s atmospheric chemistry and the first photographs of its hidden surface, and will supply a detailed ‘weather report’. One of the main reasons for sending Huygens to Titan is that its nitrogen atmosphere, rich in methane, and its surface may contain many chemicals of the kind that existed on the young Earth. Combined with the Cassini observations, Huygens will afford an unprecedented view of Saturn’s mysterious moon. “Descending through Titan was a once-in-a-lifetime opportunity and today’s achievement proves that our partnership with ESA was an excellent one,” says Alphonso Diaz, NASA Associate Administrator of Science. The Cassini-Huygens mission is a cooperation between NASA, the European Space Agency and ASI, the Italian space agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, is managing the mission for NASA’s Office of Space Science, Washington. JPL designed, developed and assembled the Cassini orbiter. “The teamwork in Europe and the USA, between scientists, industry and agencies has been extraordinary and has set the foundation for today’s enormous success,” concludes Jean-Jacques Dordain. Source: ESA

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In the largest galaxy survey ever, the Sloan Digital Sky Survey (SDSS) confirmed the role of gravity in growing structures in the universe, using the result to precisely measure the geometry of the universe. The SDSS researchers from the University of Arizona, New York University, the University of Portsmouth (UK), the University of Pittsburgh and the Massachusetts Institute of Technology, detected ripples in the galaxy distribution made by sound waves generated soon after the Big Bang. "These sound waves left their imprint in the Cosmic Microwave Background, remnant radiation from the Big Bang seen when the universe was 400,000 years old," lead investigator Daniel Eisenstein of the University of Arizona said. "We are now seeing the corresponding cosmic ripples in the SDSS galaxy maps. Seeing the same ripples in the early universe and the relatively nearby galaxies is smoking-gun evidence that the distribution of galaxies today grew via gravity." Eisenstein made the announcement today during a press conference at the winter meeting of the American Astronomical Society in San Diego. The paper, "Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies" was submitted for publication to the Astrophysical Journal on December 31, 2004. Ripples as yardsticks The early Universe was smooth and homogenous, quite a contrast from the clumpy array of galaxies and clusters of galaxies observed today. One of the major goals of cosmology is to understand how these structures grew out of the initially smooth universe. The galaxies we see today consist of ordinary matter, made up of the atoms of our familiar world. However, astronomers have long known that there is roughly five times more 'dark matter' than ordinary or 'baryonic' matter. Understanding how gravity causes the clumps that will become galaxies and clusters of galaxies to grow as the universe expands requires studying the interaction between ordinary and dark matter. "In the early Universe, the interaction between gravity and pressure caused a region of space with more ordinary matter than average to oscillate, sending out waves very much like the ripples in a pond when you throw in a peeble," explains SDSS scientist and co-author Bob Nichol, an astrophysicist at the Institute of Cosmology & Gravitation at the University of Portsmouth (UK), the most recent institution to join the SDSS collaboration. "These ripples in the matter grew for a million years until the Universe cooled enough to freeze them in place. What we now see in the SDSS galaxy data is the imprint of these ripples billions of years later." Or gravity's signature could be likened to a ringing bell's resonance in time and space, adds Idit Zehavi of the University of Arizona. "This last ring gets forever quieter and deeper in tone as the Universe expands. It is now so faint as to be detectable only by the most sensitive surveys," Zehavi explains. "The SDSS has measured the tone of this last ring very accurately. "Comparing the measured value with that predicted gives a yardstick that enables us to determine the rate at which the universe expands, which in turn depends on the amount of both dark matter and dark energy," Zehavi explains. Dark energy is the still mysterious force driving the acceleration and expansion of the Universe today. Waves separated by 500 million light years The sound waves propagated for the first million years of the Universe's history. Their existence was first predicted in 1970 and they were first seen in 1999 in fluctuations in the remnant light from the hot glow of the Big Bang known as the Cosmic Microwave Background. It had long been suggested that these sound waves should also be present in the distribution of galaxies, but the signal was predicted to be subtle and difficult to discern. To find the signal, the SDSS team mapped more than 46,000 very luminous red galaxies over a volume of space roughly five billion light years in diameter. They found a slight excess of galaxies with separations of 500 million light years, exactly the predicted signature of the sound waves. "This is just the scale predicted for these ripples", explained David Hogg of New York University, a member of the team. "The precise determination of the distance between ripples allows us to set the scale of the expansion of the universe, which in turn allows us to constrain the properties of both dark matter and dark energy." SDSS team member Kazuhiro Yahata of the University of Tokyo led a complementary analysis of quasar clustering and credits the huge volume of SDSS data that allows such findings. While Yahata's analysis did not directly detect the 500 million light year yardstick in the quasar distribution, its results are fully consistent with the presence of sound waves. A similar analysis on a different dataset by the Two Degree Field Galaxy Redshift Survey has also detected the sound waves. "It is impressive verification of the standard cosmological model that two groups with independent data have both made significant detections of the baryon induced features in large-scale galaxy clustering," said Shaun Cole of the University of Durham (UK), lead author of the Two Degree Field study. "The amazing thing about all these results is that they are in perfect accord with the predictions of our standard cosmological model, including both dark matter and dark energy," says Eisenstein. "So while it all fits together, it still leaves us 'in the dark' about the nature of these two mysterious components which dominate the energy of the universe." Source: University of Arizona

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http://www.hypography.com/gallery/files/5/huygens_rentree_l_thumb.jpgHere is an updated timeline for the descent of the Huygens spacecraft through Titan's atmosphere on Friday, 15 january 2005. All times below are Earth received time, Central european Time (ie, GMT+1). Actual spacecraft events occur 67 minutes earlier, as this is the time taken for signals to reach Earth from Cassini. 10.51 Huygens turns transmitters on Although Huygens cannot contact Cassini during the first part of the descent, it turns on its transmitters in preparation. 11.13Huygens reaches 'interface altitude' The 'interface altitude' is defined as 1270 kilometres above the surface of the moon where entry into Titan's atmosphere takes place. 11.16 Pilot parachute deploys The parachute deploys when Huygens detects that it has slowed to 400 metres per second, at about 180 kilometres above Titan's surface. The pilot parachute is the probe's smallest, only 2.6 metres in diameter. Its sole purpose is to pull off the probe's rear cover, which protected Huygens from the frictional heat of entry. 2.5 seconds after the pilot parachute is deployed, the rear cover is released and the pilot parachute is pulled away. The main parachute, which is 8.3 metres in diameter, unfurls. 11.17 Huygens begins transmitting to Cassini and front shield released At about 160 kilometres above the surface, the front shield is released. 42 seconds after the pilot parachute is deployed, inlet ports are opened up for the Gas Chromatograph Mass Spectrometer and Aerosol Collector Pyrolyser instruments, and booms are extended to expose the Huygens Atmospheric Structure Instruments. The Descent Imager/Spectral Radiometer will capture its first panorama, and it will continue capturing images and spectral data throughout the descent. The Surface Science Package will also be switched on, measuring atmospheric properties. 11.32 Main parachute separates and drogue parachute deploys The drogue parachute is 3 metres in diameter. At this level in the atmosphere, about 125 metres in altitude, the large main parachute would slow Huygens down so much that the batteries would not last for the entire descent to the surface. The drogue parachute will allow it to descend at the right pace to gather the maximum amount of data. 11.49 Surface proximity sensor activated Until this point, all of Huygens's actions have been based on clock timers. At a height of 60 kilometres, it will be able to detect its own altitude using a pair of radar altimeters, which will be able to measure the exact distance to the surface. The probe will constantly monitor its spin rate and altitude and feed this information to the science instruments. All times after this are approximate. 11.56 Possible icing effects to probe The probe has been designed to withstand possible icing as it descends to 50 kilometres above the surface, through the coldest part of the atmosphere. 12.57 Gas Chromatograph Mass Spectrometer begins sampling atmosphere This is the last of Huygens's instruments to be activated fully. The descent is expected to take 137 minutes in total, plus or minus 15 minutes. Throughout its descent, the spacecraft will continue to spin at a rate of between 1 and 20 rotations per minute, allowing the camera and other instruments to see the entire panorama around the descending spacecraft. 13.30 Descent Imager/Spectral Radiometer lamp turned on Close to the surface, Huygens's camera instrument will turn on a light. The light is particularly important for the 'Spectral Radiometer' part of the instrument to determine the composition of Titan's surface accurately. 13.34 Surface touchdown This time may vary by plus or minus 15 minutes depending on how Titan's atmosphere and winds affect Huygens's parachuting descent. Huygens will hit the surface at a speed of 5-6 metres per second. Huygens could land on a hard surface of rock or ice or possibly land on an ethane sea. In either case, Huygens's Surface Science Package is designed to capture every piece of information about the surface that can be determined in the three remaining minutes that Huygens is designed to survive after landing. 15.44 Cassini stops collecting data Huygens's landing site drops below Titan's horizon as seen by Cassini and the orbiter stops collecting data. Cassini will listen for Huygens's signal as long as there is the slightest possibility that it can be detected. Once Huygens's landing site disappears below the horizon, there's no more chance of signal, and Huygens's work is finished. 16.24 First data received on Earth Getting data from Cassini to Earth is now routine, but for the Huygens mission, additional safeguards are put in place to make sure that none of Huygens's data are lost. Giant radio antennas around the world will listen for Cassini as the orbiter relays repeated copies of Huygens data. Updated info can be found at: http://www.esa.int/SPECIALS/Cassini-Huygens/SEMXYGQ3K3E_0.html

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A trio of massive, young star clusters found embedded in a star cloud may shed light on the formation of super-star clusters and globular clusters. The discovery, made with images taken with the Hubble Space Telescope, is being presented today by You-Hua Chu and Rosie Chen of the University of Illinois at Urbana-Champaign and Kelsey Johnson of the University of Virginia to the American Astronomical Society meeting in San Diego. This finding indicates that super-star clusters may be formed by coalescence of smaller clusters. The tightly packed group of clusters was found in the core of the active star formation region NGC 5461, within an arm of the giant spiral galaxy M101. This galaxy is located about 23 million light-years away in the constellation Ursa Major (the Big Dipper). "NGC 5461 has such a high concentration of light in its core that some astronomers have thought it might host a super-star cluster," said Chu, who is a professor of astronomy at Illinois and principal investigator of the project. Super-star clusters, with a total mass of up to 1 million times that of the sun, are five to 50 times more massive than the spectacular R136 cluster at the center of the Tarantula Nebula in the Large Magellanic Cloud. They are believed to be the young counterparts of the massive globular clusters in our galaxy. Hubble Space Telescope images of the core of NGC 5461 revealed a tight group of three massive clusters surrounded by a cloud of stars within a region about 100 light-years in diameter. Although each cluster is comparable to the R136 cluster, the total mass within this small volume is similar to that of a super-star cluster. http://www.hypography.com/gallery/files/5/uiuc-starcluster_b011005.jpg Lower right: a blue image of the spiral galaxy M101 from the Second Palomar Observatory Sky Survey. The box marks the location of NGC 5461.Lower left: A false color image of NGC 5461 made from images taken with the Hubble Space Telescope Wide-Field Planetary Camera 2 using filters F547M, F675W, and F656N (displayed in blue, green, and red, respectively). Young stars and clusters will appear predominantly blue, while the ionized interstellar gas appears red. Credits: NASA, Y.-H. Chu and R. Chen (University of Illinois), and K. Johnson (University of Virginia). Upper left: A close-up of the core of NGC 5461 taken with the Hubble Space Telescope Advanced Camera for Surveys using the F435W filter to show the clusters and surrounding star cloud. Credits: NASA, K.D. Kuntz (University of Maryland Baltimore County). "If NGC 5461 were several times farther away, even the Hubble Space Telescope would be unable to resolve this tight group of clusters," said Chen, a graduate student at Illinois. "It is possible that some of the super-star clusters previously reported in distant galaxies actually consist of groups of clusters similar to NGC 5461." The large amount of mass at the core of NGC 5461 produces a strong gravitational field, causing the clusters and stars to move and interact dynamically. The rapidly fluctuating gravitational field produced by this interaction dissipates the relative motion of the clusters into random motions of individual stars. Eventually, the clusters and surrounding star cloud will merge into one single star cluster. "The Hubble Space Telescope images of NGC 5461 provide a unique glimpse of a super-star cluster in the making," said Johnson, a professor of astronomy at Virginia. "There is no super-star cluster yet, but it is just a matter of time." The dynamical evolution of the clusters at the core of NGC 5461 is being simulated by astronomy professor Paul Ricker at Illinois. Preliminary results show that under optimal conditions these clusters may merge within a few million years. "Fortunately, NGC 5461 is near enough, and young enough for us to resolve it with the Hubble Space Telescope," Chu said. "We were indeed lucky to catch it at such an opportune time." Source: University of Illinois at Urbana-Champaign

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NASA lit a birthday candle today for its twin Mars Exploration Rovers, Spirit and Opportunity. The Spirit rover begins its second year on Mars investigating puzzling rocks unlike any found earlier. http://www.hypography.com/gallery/files/5/rover1_400_thumb.jpg The rovers successfully completed their three-month primary missions in April. They astound even their designers with how well they continue operating. The unanticipated longevity is allowing both rovers to reach additional destinations and to keep making discoveries. Spirit landed on Jan. 3 and Opportunity Jan. 24, 2004, respectively. "You could have cut the tension here with a knife the night Spirit landed," said NASA Administrator Sean O'Keefe. "Just remembering the uncertainty involved with the landing emphasizes how exciting it is for all of us, since the rovers are still actively exploring. The rovers created an amazing amount of public interest and have certainly helped advance the Vision for Space Exploration," he said. The twin Mars explorers have drawn the most hits to NASA Web sites - - more than 9 billion in 2004. Dr. Charles Elachi, director of NASA's Jet Propulsion Laboratory, Pasadena, Calif., said, "Little did we know a year ago that we'd be celebrating a year of roving on Mars. The success of both rovers is tribute to hundreds of talented men and women who have put their knowledge and labor into this team effort." "The rovers are both in amazingly good shape for their age," said JPL's Jim Erickson, rover project manager. "The twins sailed through the worst of the martian winter with flying colors, and spring is coming. Both rovers are in strong positions to continue exploring, but we can't give you any guarantees." Opportunity is driving toward the heat shield that protected it during descent through the martian atmosphere. Rover team members hope to determine how deeply the atmospheric friction charred the protective layer. "With luck, our observations may help to improve our ability to deliver future vehicles to the surface of other planets," Erickson said. Spirit is exploring the Columbia Hills within the Gusev Crater. "In December, we discovered a completely new type of rock in Columbia Hills, unlike anything seen before on Mars," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers' science payloads. Jumbled textures of specimens dubbed "Wishstone" and "Wishing Well" look like the product of an explosion, perhaps from a volcano or a meteor impact. These rocks are much richer in phosphorus than any other known Mars rocks. "Some ways of making phosphates involve water; others do not," Squyres said. "We want to look at more of these rocks to see if we can distinguish between those possible histories." NASA's next Mars mission, the Mars Reconnaissance Orbiter, is due to launch in August. "As great as the past year has been, Mars launch opportunities come along like clockwork every 26 months," said Dr. Firouz Naderi of JPL, manager of NASA's Mars Exploration Program. "At every one of them in the foreseeable future, we intend to go to Mars, building upon the findings by the rovers." NASA Chief Scientist Dr. Jim Garvin said, "Mars lures us to explore its mysteries. It is the most Earth-like of our sister planets, and many believe it may hold clues to whether life ever existed or even originated beyond Earth. The rovers have shown us Mars had persistently wet, possibly life-sustaining environments. Beyond their own profound discoveries, the rovers have advanced our step-by- step program for examining Mars. We will continue to explore Mars robotically, and eventually with human explorers." Source: NASA/JPL

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The European Space Agency's Huygens probe successfully detached from NASA's Cassini orbiter today to begin a three-week journey to Saturn's moon Titan. http://www.hypography.com/gallery/files/5/huygens_rentree2_hires_thumb.jpg NASA's Deep Space Network tracking stations in Madrid, Spain, and Goldstone, Calif., received the signal at 7:24 p.m. (PST). All systems performed as expected and there were no problems reported with the Cassini spacecraft. The Huygens probe, built and managed by the European Space Agency, was bolted to Cassini and has been riding along during the nearly seven-year journey to Saturn largely in a "sleep" mode. Huygens will be the first human-made object to explore on-site the unique environment of Titan, whose chemistry is assumed to be very similar to that of early Earth before life formed. Huygens will tell us whether this assumption is correct. "We wish to congratulate our European partners as their journey begins and wish them well on their descent to Titan," said Robert T. Mitchell, Cassini program manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We are very excited to see the probe off and to have accomplished this part of our job. Now we're ready to finish our part -- receiving and relaying the Huygens data back to Earth." "Today's release is another successful milestone in the Cassini- Huygens odyssey," said Dr. David Southwood, director of science program for the European Space Agency. "This was an amicable separation after seven years of living together. Our thanks to our partners at NASA for the lift. Each spacecraft will now continue on its own but we expect they'll keep in touch to complete this amazing mission. Now all our hopes and expectations are focused on getting the first in-situ data from a new world we've been dreaming of exploring for decades." The Huygens probe will remain dormant until the onboard timer wakes it up just before the probe reaches Titan's upper atmosphere on Jan. 14, 2005. Then it will begin a dramatic plunge through Titan's murky atmosphere, tasting its chemical makeup and composition as it descends to touch down on its surface. The data gathered during this 2-1/2 hour descent will be transmitted from the probe to the Cassini orbiter. Afterward, Cassini will point its antenna to Earth and relay the data through NASA's Deep Space Network to JPL and on to the European Space Agency's Space Operations Center in Darmstadt, Germany, which serves as the operations center for the Huygens probe mission. From this control center, ESA engineers will be tracking the probe and scientists will be standing by to process the data from the probe's six instruments. On Monday, Dec. 27, the Cassini orbiter will perform a deflection maneuver to keep it from following Huygens into Titan's atmosphere. This maneuver will also establish the required geometry between the probe and the orbiter for radio communications during the probe descent. More information on the Cassini-Huygens mission is available at: http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. Source: NASA/JPL

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A team led by University of Maine scientists has reported finding a potential link between changes in solar activity and the Earth's climate http://www.hypography.com/newdesign/sunearth.jpgIn a paper due to be published in an upcoming volume of the Annals of Glaciology, Paul Mayewski, director of UMaine's Climate Change Institute, and 11 colleagues from China, Australia and UMaine describe evidence from ice cores pointing to an association between the waxing and waning of zonal wind strength around Antarctica and a chemical signal of changes in the sun's output. At the heart of the paper, Solar Forcing of the Polar Atmosphere, are calcium, nitrate and sodium data from ice cores collected in four Antarctic locations and comparisons of those data to South Pole ice core isotope data for beryllium-10, an indicator of solar activity. The authors also point to data from Greenland and the Canadian Yukon that suggest similar relationships between solar activity and the atmosphere in the northern hemisphere. They focus on years since 1400 when the Earth entered a roughly 500-year period known as the Little Ice Age. The researchers' goal is to understand what drives the Earth's climate system without taking increases in greenhouse gases into account, says Mayewski. "There are good reasons to be concerned about greenhouse gases, but we should be looking at the climate system with our eyes open," he adds. Understanding how the system operates in the absence of human impacts is important for responding to climate changes that might occur in the future. Mayewski founded the International Transantarctic Scientific Expedition (ITASE) and is the co-author of The Ice Chronicles: The Quest to Understand Global Climate Change, published in 2002 with Frank White. The United States' ITASE office is located at UMaine. Antarctic locations used in the paper include: Law Dome, a 4,576-foot high ice mound located about 68 miles from the coast facing the Indian Ocean and the site of an Australian research station; Siple Dome, a 2,000-foot high ice covered mound located between two ice streams that flow out of the Transantarctic Mountains into the Ross ice shelf, and the site of a U.S. research station; and two ITASE field sites west of Siple Dome where ice cores were collected during field surveys in 2000 and 2001. The authors are Mayewski, Kirk A. Maasch, Eric Meyerson, Sharon Sneed, Susan Kaspari, Daniel Dixon, and Erich Osterberg, all from UMaine; Yping Yan of the China Meterological Association; Shichang Kang of UMaine and the Chinese Academy of Sciences; and Vin Morgan, Tas van Ommen and Mark Curran of the Antarctic Climate and Ecosystems CRC in Tasmania. Since at least the 1840s when sunspot cycles were discovered, scientists have proposed that solar variability could affect the climate, but direct evidence of that relationship and understanding of a mechanism have been lacking. The ice core data show, the authors write, that when solar radiation increases, more calcium is deposited at Siple Dome and at one of the ITASE field sites. The additional calcium may reflect an increase in wind strength in mid-latitude regions around Antarctica, they add, especially over the Indian and Pacific Oceans. Calcium in West Antarctic ice cores is thought to derive mainly from dust in Australia, Africa and South America and from sea salt in the southern ocean. That finding, they note, is consistent with other research suggesting that the sun may affect the strength of those mid-latitude winds through changes in stratospheric ozone over Antarctica. The authors also refer to sodium data from Siple Dome ice cores that have been reported by Karl Kreutz, director of UMaine's stable isotope laboratory. Changes in sodium appear to be associated with air pressure changes over the South Pacific. Ice core data from Law Dome focus on changes in nitrate and may reflect changing wind patterns over Antarctica. The wind currents that bring nitrate to the continent, however, are less well known than those that carry sodium and calcium. Researchers in the UMaine Climate Change Institute (http://www.climatechange.umaine.edu/) have focused on the relationship between solar variability and climate, particularly the use of isotopes in tree rings and ice cores to provide an indication of the sun's strength. The ice core data reported in the paper demonstrates a direct atmospheric consequence associated with changing solar radiation. Source: University of Maine

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Santa will have company in the sky over most of the United States this holiday season. The International Space Station is visible in the early morning, flying by at five miles a second. Information about how, when and where to see it is available on the Internet at: http://www.jsc.nasa.gov/isssightings All sightings available from U.S. cities during the holidays are pre-dawn sightings. The Station is not expected to be visible in the evenings. The 200-ton plus Station, which is more than 170 feet long and 240 feet wide, will be visible from most continental U.S. cities, as well as Juneau, Alaska, on various days between Christmas Eve and New Year's Day. The Station's crew, Expedition 10 Commander Leroy Chiao and Flight Engineer Salizhan Sharipov, will celebrate the holidays aboard the orbiting research complex this year. Chiao and Sharipov will get a special delivery on Dec. 25 as a Russian cargo spacecraft docks with the Station. The cargo ship will bring 5,000 pounds of supplies, including food, water, fuel, spare equipment and Christmas presents from home. For those areas with opportunities to view the Station on Christmas Eve and Christmas Day mornings, the Progress cargo spacecraft also may be visible as it closes in on the Station. The Progress is scheduled to dock with the International Space Station about 7:05 p.m. EST. The docking will be carried live on NASA TV. Holiday greetings from the Station crew, video of Mission Control's season's greetings and footage of Mission Control tracking Santa Claus also are airing daily on NASA TV. Source: NASA press release

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A massive eruption of atomic oxygen from Saturn's outer rings, seen by Cassini's ultraviolet camera as the spacecraft neared its destination, may be an indication that the planet's wispy E ring is eroding so fast that it could disappear within 100 million years if not replenished. http://www.usc.edu/uscnews/stories/img/pic1_10855.gif Cassini's Ultraviolet Imaging Spectrograph (UVIS) detected the oxygen atoms spewing into a huge cloud on the dark side of Saturn's rings as Cassini prepared to enter orbit around Saturn in January 2004, said Donald Shemansky, professor of aerospace and mechanical engineering in the University of Southern California Viterbi School of Engineering and a co-investigator on the Cassini ultraviolet imaging team. Data indicated that about 275 million pounds (125 million kilograms) of oxygen was abruptly released in a short period of time. "This was our first surprise in the ultraviolet," said Shemansky, who will analyze ultraviolet data during Cassini's four-year tour of Saturn and its rings with Janet Hallett, a postdoctoral aerospace research associate in the USC Viterbi School. "We aren't sure yet whether this was a transient event or part of a routine recycling process in Saturn's magnetosphere," he said. "Right now scientists are speculating that the oxygen eruption may have been caused by a collision of ice particles from the planet's distant E ring with material in one of the main ring systems, A, B or C. Or it could have been a meteorite collision or an eruption of icy slush on Enceladus, a moon that orbits in the E ring." Shemansky and the 16-member Cassini ultraviolet imaging team reported their findings in the Dec. 16, 2004 issue of Science Express (see http://www.sciencexpress.org magazine). Despite Saturn's placid appearance from Earth, the planet is anything but that. The first detailed UV images from the Cassini mission show that Saturn commands a dynamic world of complex, braided ice rings, cannibalistic moons, 1,100 mile-per-hour planetary winds and electrifying auroral displays high in the night skies. Saturn, its moons and highly structured rings live inside a huge cavity in the solar wind created by the planet's strong magnetic field. The magnetosphere is a bubble of particles including electrons, various species of ions, neutral atoms and molecules, several populations of very energetic charged particles like those found in Earth's Van Allen Belts, and charged dust grains. These ionized (electrically charged) gases are called plasmas. However, unlike Jupiter's magnetosphere, Shemansky said Saturn's magnetic cocoon, which is smaller, is filled primarily with neutral gas rather than ions. "Saturn's magnetosphere is turning out to be very different from Jupiter's," he said. "It's dominated by neutral gas and water-rich ingredients produced by its rings, as icy moon debris collides, or by the more energetic collisions of incoming meteorites. It doesn't have nearly as many charged particles, and many of them are absorbed by the rings, so the plasma processes we are observing are entirely different." Two months after his initial observations, Shemansky and his ultraviolet team reported that the large cloud of escaping oxygen atoms had dissipated just as rapidly as it had appeared. Shemansky discounted theories that the rapid loss of material could be explained by "satellite sweeping," a process whereby tiny shepherding moons gobble up debris or deflect it as they clean out gaps between the rings. "The rate at which we saw material escaping from Saturn's outer rings implies that mass equivalent to the entire E ring, even including larger fragments and parent bodies, would be consumed in a period of about 100 million years if no replenishment processes are at work," he said. The rings of gas giants are made up of rocky debris from moons that have been torn apart by tidal waves or by an asteroid or comet collision during heavy bombardment periods. Rings are considered ephemeral and thought to disappear over time spans of billions of years. But Saturn's colorful rings appear to be younger. Scientists think the rings are much younger than the planet itself – perhaps only 100 million years old – which is young in cosmological time. They also suspect that Saturn has had several ring systems in its history, although they have never had direct evidence on which to base their assumptions. "These observations are a first in solar system exploration," Shemansky said. "We have direct evidence now that the rings are made up of pure ice and that they are shaped by processes that happen fast," he added. "They aren't the same processes that shaped our solar system 4.5 billion years ago. "Given the fact that the outer rings are present at this time means that the system is being replenished by interactive plasma processes," Shemansky continued. "Clearly, the fact that something is eating up micron-sized grains in the outer ring zones at a high rate tells us that some sort of recycling process must be going on to rebuild them." Cassini's UV imaging spectrograph has made other important observations. In the ultraviolet, scientists were able to see dust on the rings. Data showed variations in the amount of water-ice contained in the surfaces of ring particles, suggesting that darkened portions had been dusted with powder from pulverized moons or incoming meteoroids. The Cassini UVIS team also obtained ultraviolet images of Phoebe, Saturn's most distant large moon, during the inbound flight to Saturn. Data showed the absorption lines of water-ice on Phoebe's dark surface, which gave scientists more clues about its origins. The only moon in the Saturnian system to orbit in a retrograde, or backward, direction, Phoebe is similar to a common C-type carbonaceous asteroid. Scientists theorize that it was flung out of the Kuiper Belt, a region well beyond Neptune's orbit where thousands of small, icy comets reside, and sucked up by Saturn's strong gravitational field, but no one is absolutely sure of its origin. The Cassini-Huygens spacecraft and science instruments are part of an international mission by NASA, the European Space Agency and the Italian Space Agency to explore Saturn and its many moons and rings. Source: University of Southern California