Tenth Planet Has a Moon

PASADENA, Calif. --The newly discovered 10th planet, 2003 UB313, is looking more and more like one of the solar system's major players. It has the heft of a real planet (latest estimates put it at about 20 percent larger than Pluto), a catchy code name (Xena, after the TV warrior princess), and a Guinness Book-ish record of its own (at about 97 astronomical units-or 9 billion miles from the sun-it is the solar system's farthest detected object). And, astronomers from the California Institute of Technology and their colleagues have now discovered, it has a moon.

The moon, 100 times fainter than Xena and orbiting the planet once every couple of weeks, was spotted on September 10, 2005, with the 10-meter Keck II telescope at the W.M. Keck Observatory in Hawaii by Michael E. Brown, professor of planetary astronomy, and his colleagues at Caltech, the Keck Observatory, Yale University, and the Gemini Observatory in Hawaii. The research was partly funded by NASA. A paper about the discovery was submitted on October 3 to Astrophysical Journal Letters.

"Since the day we discovered Xena, the big question has been whether or not it has a moon," says Brown. "Having a moon is just inherently cool-and it is something that most self-respecting planets have, so it is good to see that this one does too."

Brown estimates that the moon, nicknamed "Gabrielle"-after the fictional Xena's fictional sidekick-is at least one-tenth of the size of Xena, which is thought to be about 2700 km in diameter (Pluto is 2274 km), and may be around 250 km across.

To know Gabrielle's size more precisely, the researchers need to know the moon's composition, which has not yet been determined. Most objects in the Kuiper Belt, the massive swath of miniplanets that stretches from beyond Neptune out into the distant fringes of the solar system, are about half rock and half water ice. Since a half-rock, half-ice surface reflects a fairly predictable amount of sunlight, a general estimate of the size of an object with that composition can be made. Very icy objects, however, reflect a lot more light, and so will appear brighter-and thus bigger-than similarly sized rocky objects.

Further observations of the moon with NASA's Hubble Space Telescope, planned for November and December, will allow Brown and his colleagues to pin down Gabrielle's exact orbit around Xena. With that data, they will be able to calculate Xena's mass, using a formula first devised some 300 years ago by Isaac Newton.

"A combination of the distance of the moon from the planet and the speed it goes around the planet tells you very precisely what the mass of the planet is," explains Brown. "If the planet is very massive, the moon will go around very fast; if it is less massive, the moon will travel more slowly. It is the only way we could ever measure the mass of Xena-because it has a moon."

The researchers discovered Gabrielle using Keck II's recently commissioned Laser Guide Star Adaptive Optics system. Adaptive optics is a technique that removes the blurring of atmospheric turbulence, creating images as sharp as would be obtained from space-based telescopes. The new laser guide star system allows researchers to create an artificial "star" by bouncing a laser beam off a layer of the atmosphere about 75 miles above the ground. Bright stars located near the object of interest are used as the reference point for the adaptive optics corrections. Since no bright stars are naturally found near Xena, adaptive optics imaging would have been impossible without the laser system.

"With Laser Guide Star Adaptive Optics, observers not only get more resolution, but the light from distant objects is concentrated over a much smaller area of the sky, making faint detections possible," says Marcos van Dam, adaptive optics scientist at the W.M. Keck Observatory, and second author on the new paper.

The new system also allowed Brown and his colleagues to observe a small moon in January around 2003 EL61, code-named "Santa," another large new Kuiper Belt object. No moon was spotted around 2005 FY9-or "Easterbunny"-the third of the three big Kuiper Belt objects recently discovered by Brown and his colleagues using the 48-inch Samuel Oschin Telescope at Palomar Observatory. But the presence of moons around three of the Kuiper Belt's four largest objects-Xena, Santa, and Pluto-challenges conventional ideas about how worlds in this region of the solar system acquire satellites.

Previously, researchers believed that Kuiper Belt objects obtained moons through a process called gravitational capture, in which two formerly separate objects moved too close to one another and become entrapped in each other's gravitational embrace. This was thought to be true of the Kuiper Belt's small denizens-but not, however, of Pluto. Pluto's massive, closely orbiting moon, Charon, broke off the planet billions of years ago, after it was smashed by another Kuiper Belt object. Xena's and Santa's moons appear best explained by a similar origin.

"Pluto once seemed a unique oddball at the fringe of the solar system," Brown says. "But we now see that Xena, Pluto, and the others are part of a diverse family of large objects with similar characteristics, histories, and even moons, which together will teach us much more about the solar system than any single oddball ever would."

Brown's research is partly funded by NASA.

For more information on the discovery and on Xena, visit www.gps.caltech.edu/~mbrown/planetlila

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Contact: Kathy Svitil (626) 395-8022 ksvitil@caltech.edu

Visit the Caltech Media Relations Web site at: http://pr.caltech.edu/media

 

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KS
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Work Continues on the Solar System's Three Recently Discovered Objects

CAMBRIDGE, England--When planetary scientists announced on July 29 that they had discovered a new planet larger than Pluto, the news overshadowed the two other objects the group had also found. But all three objects are odd additions to the solar system, and as such could revolutionize our understanding of how our part of the celestial neighborhood evolved.

To the discoverers, the objects still go by the unofficial code-names "Santa," "Easterbunny," and "Xena," though they are officially known to the International Astronomical Union as 2003 EL61, 2005 FY9, and 2003 UB313. The three objects were all detected with the 48-inch Samuel Oschin Telescope at Palomar Observatory by a team composed of planetary scientists from the California Institute of Technology, the Gemini Observatory, and Yale University. Xena is the object the group describes as one of sufficient size to be called the tenth planet.

"All three objects are nearly Pluto-sized or larger, and all are in elliptical orbits tilted out of the plane of the solar system," says Mike Brown, a professor of planetary astronomy at Caltech and leader of the effort.

"We think that these orbital characteristics may mean that they were all formed closer to the sun, and then were tossed around by the giant planets before they ended up with the odd orbits they currently have," Brown adds.

The other two members of the team are Chad Trujillo, a former postdoctoral researcher at Caltech and currently an astronomer at the Gemini Observatory in Hawaii, and David Rabinowitz of Yale University. Trujillo has led the spectrographic studies of the discoveries, while Rabinowitz is one of the builders of the instrument affixed to the Oschin Telescope for the study, and has led the effort to understand the color and spin of the objects.

Santa, Easterbunny, and Xena are all members of the Kuiper belt, a region beyond the orbit of Neptune that for decades was merely a hypothetical construct based on the behavior of comets, among other factors. But astronomers began detecting objects in the mid-1990s, and the Kuiper belt was suddenly a reality rather than a hypothesis.

Xena, which is currently about 97 astronomical units from the sun (an astronomical unit being the 93-million-mile distance between the sun and Earth), is at least the size of Pluto and almost certainly significantly larger. The researchers are able to determine its smallest possible size because, thanks to the laws of motion, they know very accurately the distance of the planet from the sun. And because they also know very precisely how much light the planet gives off, they can also calculate the diameter of the planet as if it were reflecting sunlight as a uniformly white ball in the sky. Hence, a perfectly round mirror at that distance would be the size of Pluto.

However, the question remains how well the new planet reflects light. The less reflective its surface, the bigger it must be to put out enough light to be detected here on Earth.

At any rate, the researchers hope that infrared data returned by the Spitzer Space Telescope over the weekend of August 27-28, in addition to recently obtained data from the 30-meter IRAM telescope in Spain, will help nail down Xena's size. In much the same way that the detected visible light sets a lower limit on the diameter, the infrared radiation detected by the Spitzer will ideally set an upper limit. That's because the Spitzer is capable of measuring the total amount of heat given off by the planet; and because the researchers know the likely surface temperature is about 405 degrees below zero Fahrenheit, they can infer the overall size of the body.

Brown predicts that Xena will likely be highly reflective, because the spectrographic data gathered by his colleague and codiscoverer Chad Trujillo at the Gemini Observatory show the surface to have a similar composition to that of the highly reflective Pluto. If indeed Xena reflects 70 percent of the sunlight reaching it, as does Pluto, then Xena is about 2700 kilometers in diameter.

And then there's the matter of naming the new planet, which is pretty much in the hands of the International Astronomical Union. Brown says the matter is in "committee limbo": while one IAU committee is taking its time deciding whether or not it is a planet, other committees have to wait until they know what it is before they can consider a name. So for the time being, the discoverers keep calling the new planet Xena, though the name will sooner or later change.

The second of the objects, currently nicknamed Santa because Brown and his colleagues found it on December 28, 2004, is one of the more bizarre objects in the solar system, according to Rabinowitz. His observations from a small telescope in Chile show that Santa is a fast-rotating cigar-shaped body that is about the diameter of Pluto along its longer axis. No large body in the solar system comes even close to rotating as fast as Santa's four-hour period. Observations by Brown and his colleagues at the Keck Observatory have shown that Santa also has a tiny moon, nicknamed Rudolph, which circles it every 49 days. The third new discovery is Easterbunny, so named because of its discovery earlier this year on March 1. Easterbunny is also at 52 astronomical units, and like Santa is probably about three-quarters the size of Pluto. Morever, Easterbunny is now the third known object in the Kuiper belt, after Pluto and Xena, which is known to have a surface covered in frozen methane. For decades, Pluto was the only known methane-covered object beyond Neptune, but "now we suddenly have three in a variety of sizes at a variety of distances and can finally try to understand Pluto and its cousins," says Kris Barkume, a PhD student working with Brown.

"With so many bright objects coming out at once it is hard to keep them all straight," says Brown, adding that the remote region beyond Neptune may present even more surprises in the future.

"We hope to discover a few more large objects in the outer solar system."

The research is funded by NASA. For more information see http://www.gps.caltech.edu/~mbrown

 

 

Writer: 
Robert Tindol
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Evolutionary Accident Probably Caused The Worst Snowball Earth Episode, Study Shows

PASADENA--For several years geologists have been gathering evidence indicating that Earth has gone into a deep freeze on several occasions, with ice covering even the equator and with potentially devastating consequences for life. The theory, known as "Snowball Earth," has been lacking a good explanation for what triggered the global glaciations.

Now, the California Institute of Technology research group that originated the Snowball Earth theory has proposed that the culprit for the earliest and most severe episode may have been lowly bacteria that, by releasing oxygen, destroyed a key gas keeping the planet warm.

In the current issue of the Proceedings of the National Academy of Sciences (PNAS), Caltech graduate student Robert Kopp and his supervising professor, Joe Kirschvink, along with alumnus Isaac Hilburn (now a graduate student at the Massachusetts Institute of Technology) and graduate student Cody Nash, argue that cyanobacteria (or blue-green algae) suddenly evolved the ability to break water and release oxygen about 2.3 billion years ago. Oxygen destroyed the greenhouse gas methane that was then abundant in the atmosphere, throwing the global climate completely out of kilter.

Though the younger sun was only about 85 percent as bright as it is now, average temperatures were comparable to those of today. This state of affairs, many researchers believe, was due to the abundance of methane, known commercially as natural gas. Just as they do in kitchen ranges, methane and oxygen in the atmosphere make an unstable combination; in nature they react in a matter of years to produce carbon dioxide and water. Though carbon dioxide is also a greenhouse gas, methane is dozens of times more so.

The problem began when cyanobacteria evolved into the first organisms able to use water in photosynthesis, releasing oxygen into the environment as a waste product. More primitive bacteria depend upon soluble iron or sulfides for use in photosynthesis; the switch to water allowed them to grow almost everywhere that had light and nutrients. Many experts think this happened early in Earth history, between 3.8 and 2.7 billion years ago, in which case some process must have kept the cyanobacteria from destroying the methane greenhouse for hundreds of millions of years. The Caltech researchers, however, find no hard evidence in the rocks to show that the switch to water for photosynthesis occurred prior to 2.3 billion years ago, which is about when the Paleoproterozoic Snowball Earth was triggered.

For cyanobacteria to trigger the rapid onset of a Snowball Earth, they must have had an ample supply of key nutrients like phosphorous and iron. Nutrient availability is why cyanobacterial blooms occur today in regions with heavy agricultural runoff.

Fortunately for the bacteria, Earth 2.3 billion years ago had already entered a moderately cold period, reflected in glacially formed rocks in Canada. Measurements of the magnetization of these Canadian rocks, which the Caltech group published earlier this year, indicate that the glaciers that formed them may have been at middle latitudes, just like the glaciers of the last ice age.

The action of the glaciers, grinding continental material into powder and carrying it into the oceans, would have made the oceans rich in nutrients. Once cyanobacteria evolved this new oxygen-releasing ability, they could feast on this cornucopia, turning an ordinary glaciation into a global one.

"Their greater range should have allowed the cyanobacteria to come to dominate life on Earth quickly and start releasing large amounts of oxygen," Kopp says.

This was bad for the climate because the oxygen destabilized the methane greenhouse. Kopp and Kirschvink's model shows that the greenhouse may have been destroyed in as little as 100,000 years, but almost certainly was eliminated within several million years of the cyanobacteria's evolution into an oxygen-generating organism. Without the methane greenhouse, global temperatures plummeted to -50 degrees Celsius.

The planet went into a glacial period so cold that even equatorial oceans were covered with a mile-thick layer of ice. The vast majority of living organisms died, and those that survived, either underground or at hydrothermal vents and springs, were probably forced into bare subsistence. If correct, the authors note, then an evolutionary accident triggered the world's worst climate disaster.

However, in evolving to cope with the new influx of oxygen, many survivors gained the ability to breathe it. This metabolic process was capable of releasing much energy and eventually allowing the evolution of all higher forms of life.

Kirschvink and his lab have earlier shown a mechanism by which Earth could have gotten out of Snowball Earth. After some tens of millions of years, carbon dioxide would build up to the point that another greenhouse took place. In fact, the global temperature probably bounced back to +50 degrees Celsius, and the deep-sea vents that provided a refuge for living organisms also had steadily released various trace metals and nutrients. So not only did life return after the ice layers melted, but it did so with a magnificent bloom.

"It was a close call to a planetary destruction," says Kirschvink. "If Earth had been a bit further from the sun, the temperature at the poles could have dropped enough to freeze the carbon dioxide into dry ice, robbing us of this greenhouse escape from Snowball Earth."

Of course, 2.3 billion years is a very long time ago. But the episode points to a grim reality for the human race if conditions ever resulted in another Snowball Earth. We who are living today will never see it, but Kirschvink says that an even worse Snowball Earth could occur if the conditions were again right.

"We could still go into Snowball if we goof up the environment badly enough," he says. "We haven't had a Snowball in the past 630 million years, and because the sun is warmer now it may be harder to get into the right condition. But if it ever happens, all life on Earth would likely be destroyed. We could probably get out only by becoming a runaway greenhouse planet like Venus."

Kirschvink is Caltech's Van Wingen Professor of Geobiology.

The PNAS paper is titled "The Paleoproterozoic Snowball Earth: A Climate Disaster Triggered by the Evolution of Oxygenic Photosynthesis."

 

 

 

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Robert Tindol
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Planetary Scientists Discover Tenth Planet

PASADENA, Calif.--A planet larger than Pluto has been discovered in the outlying regions of the solar system with the Samuel Oschin Telescope at Palomar Observatory, California Institute of Technology planetary scientist Mike Brown announced today.

The planet is a typical member of the Kuiper belt, but its sheer size in relation to the nine planets already known means that it can only be classified as a planet, Brown says. Currently about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), the planet becomes the farthest-known object in the solar system, and the third brightest of the Kuiper belt objects.

"It will be visible over the next six months and is currently almost directly overhead in the early-morning eastern sky, in the constellation Cetus," says Brown, who made the discovery with colleagues Chad Trujillo, of the Gemini Observatory, and David Rabinowitz, of Yale University, on January 8.

Brown and Trujillo first photographed the new planet with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of this year. In the last seven months, the scientists have been studying the planet to better estimate its size and its motions.

"It's definitely bigger than Pluto," says Brown, who is professor of planetary astronomy. Scientists can infer the size of a solar-system object by its brightness, just as one can infer the size of a faraway light bulb if one knows its wattage. The reflectance of the planet is not yet known--in other words, it's not yet possible to tell how much light from the sun is reflected away--but the amount of light the planet reflects puts a lower limit on its size.

"Even if it reflected 100 percent of the light reaching it, it would still be as big as Pluto," says Brown. "I'd say it's probably one and a half times the size of Pluto, but we're not sure yet of the final size.

"But we are 100 percent confident that this is the first object bigger than Pluto ever found in the outer solar system."

Determination of the upper limit of the size of the planet is constrained by results from the Spitzer Space Telescope, which has already proved its mettle in studying the heat of dim, faint, faraway objects such as the Kuiper-belt bodies. Because the Spitzer is unable to detect the new planet, the overall diameter must be less than 3,000 kilometers, Brown says. A name for the new planet has been proposed by the discoverers to the International Astronomical Union, and they are awaiting the decision of this body before announcing the name.

The research is funded by NASA. For more information see http://www.gps.caltech.edu/~mbrown

Samuel Oschin Telescope: http://www.astro.caltech.edu/palomarnew/sot.html

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RT

KamLAND Detector Provides New Way to Study Heat from Radioactive Materials Within Earth

PASADENA, Calif.--Much of the heat within our planet is caused by the radioactive decay of the elements uranium and thorium. Now, an international team of particle physicists using a special detector in Japan has demonstrated a novel method of measuring that radioactive heat.

In the July 28 issue of the journal Nature, the physicists report on measurements of electron antineutrinos they have detected from within Earth by using KamLAND, the Kamioka Liquid Scintillator Anti-Neutrino Detector. These data indicate that Earth itself generates about 20 billion kilowatts (or terawatts) of power from underground radioactive decays.

According to Robert McKeown, a physicist at the California Institute of Technology and one of the authors of the paper, the results show that this novel approach to geophysical research is feasible. "Neutrinos and their corresponding antiparticles, antineutrinos, are remarkable for their ability to pass unhindered through large bodies of matter like the entire Earth, and so can give geophysicists a powerful method to access the composition of the planet's interior."

McKeown credits the discovery with the unique KamLAND experimental apparatus. The antineutrino detector was primarily built to study antineutrinos emitted by Japanese nuclear power plants. The KamLAND experiment has already resulted in several breakthroughs in experimental particle physics, including the 2002 discovery that antineutrinos emitted by the power plants do indeed change flavor as they travel through space. This result helped solve a longstanding mystery related to the fact that the number of neutrinos from the sun was apparently too small to be reconciled with our current understanding of nuclear fusion. The new results turn from nuclear reactors and the sun to the Earth below. To detect geoneutrinos (or antineutrinos arising from radioactive decays within the planet), the researchers carefully shielded the detector from background radiation and cosmic sources, and also compensated for the antineutrinos that have come from Japan's 53 nuclear power reactors.

The decays of both uranium and thorium have been well understood for decades, with both decays eventually resulting in stable isotopes of lead. KamLAND is the first detector built with the capability to detect the antineutrinos from these radioactive decays.

The researchers plan to continue running the KamLAND experiments for several years. By reducing the trace residual radioactivity in the detector, they hope to increase the sensitivity of the experiment to geoneutrinos and neutrinos from the sun. The additional data will also allow them to better constrain the oscillation of neutrinos as they change their flavors, and perhaps to catch neutrinos from interstellar space if any supernovae occur in our galaxy.

Other members of McKeown's team at Caltech's Kellogg Radiation Lab are Christopher Mauger, a postdoctoral scholar in physics, and Petr Vogel, a senior research associate emeritus in physics. Other partners in the study include the Research Center for Neutrino Science at Tohuku University in Japan, the University of Alabama, the University of California at Berkeley and the Lawrence Berkeley National Laboratory, Drexel University, the University of Hawaii, the University of New Mexico, the University of North Carolina, Kansas State University, Louisiana State University, Stanford University, Duke University, North Carolina State University, the University of Tennessee, the Institute of High Energy Physics in Beijing, and the University of Bordeaux in France.

The project is supported in part by the U.S. Department of Energy.

 

 

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Robert Tindol
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Mars Has Been in the Deep Freeze for the Past Four Billion Years, Study Shows

PASADENA, Calif.--The current mean temperature on the equator of Mars is a blustery 69 degrees below zero Fahrenheit. Scientists have long thought that the Red Planet was once temperate enough for water to have existed on the surface, and for life to possibly have evolved. But a new study by Caltech and MIT scientists gives this idea the cold shoulder.

In the July 22 issue of the journal Science, Caltech graduate student David Shuster and MIT assistant professor Benjamin Weiss (formerly a Caltech student) report that their studies of Martian meteorites demonstrate that at least several rocks originally located near the surface of Mars have been freezing cold for four billion years. Their work is a novel approach to extracting information on the past climate of Mars through the study of Martian meteorites.

In fact, the evidence shows that during the last four billion years, Mars has likely never been sufficiently warm for liquid water to have flowed on the surface for extended periods of time. This implies that Mars has probably never had a hospitable environment for life to have evolved, unless life could have gotten started during the first half-billion years of its existence, when the planet was probably warmer.

The work involves two of the seven known "nakhlite" meteorites (named after El Nakhla, Egypt, where the first such meteorite was discovered), and the celebrated ALH84001 meteorite that some scientists believe shows evidence of microbial activity on Mars. Using geochemical techniques, Shuster and Weiss reconstructed a "thermal history" for each of the meteorites to estimate the maximum long-term average temperatures to which they were subjected.

"We looked at meteorites in two ways," says Weiss. "First, we evaluated what the meteorites could have experienced during ejection from Mars, 11 to 15 million years ago, in order to set an upper limit on the temperatures in a worst-case scenario for shock-heating."

Their conclusions were that ALH84001 could never have been heated to a temperature higher than 650 degrees Fahrenheit for even a brief period of time during the last 15 million years. The nakhlites, which show very little evidence of shock-damage, were unlikely to have been above the boiling point of water during ejection 11 million years ago.

Although these are still rather high temperatures, the other part of the research addressed the long-term thermal history of the rocks while they resided on Mars. They did this by estimating the total amount of argon still remaining in the samples, using data previously published by two teams at the University of Arizona and the NASA Johnson Space Center.

The gas argon is present in the meteorites as well as in many rocks on Earth as a natural consequence of the radioactive decay of potassium. As a noble gas, argon is not very chemically reactive, and because the decay rate is precisely known, geologists for years have measured argon as a means of dating rocks.

However, argon is also known to "leak" out of rocks at a temperature-dependent rate. This means that if the argon remaining in the rocks is measured, an inference can be made about the maximum heat to which the rock has been subjected since the argon was first made. The cooler the rock has been, the more argon will have been retained. Shuster and Weiss's analysis found that only a tiny fraction of the argon that was originally produced in the meteorite samples has been lost through the eons. "The small amount of argon loss that has apparently taken place in these meteorites is remarkable. Any way we look at it, these rocks have been cold for a very long time," says Shuster. Their calculations suggest that the Martian surface has been in deep-freeze for most of the last four billion years.

"The temperature histories of these two planets are truly different. On Earth, you couldn't find a single rock that has been below even room temperature for that long," says Shuster. The ALH84001 meteorite, in fact, couldn't have been above freezing for more than a million years during the last 3.5 billion years of history.

"Our research doesn't mean that there weren't pockets of isolated water in geothermal springs for long periods of time, but suggests instead that there haven't been large areas of free-standing water for four billion years.

"Our results seem to imply that surface features indicating the presence and flow of liquid water formed over relatively short time periods," says Shuster.

On a positive note for astrobiology, however, Weiss says that the new study does nothing to disprove the theory of "panspermia," which holds that life can jump from one planet to another by meteorites. Weiss and his supervising professor at Caltech, Joe Kirschvink (the Van Wingen Professor of Geobiology), several years ago showed that microbes could indeed have traveled from Mars to Earth in the hairline fractures of ALH84001 without having been destroyed by heat. In particular, the fact that the nakhlites have never been heated above about 200 degrees Fahrenheit means that they were not heat-sterilized during ejection from Mars and transfer to Earth.

The title of the new paper is "Martian Surface Paleotemperatures from Thermochronology of Meteorites."

 

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Robert Tindol
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First Planet Under Three Suns Is Discovered

PASADENA, Calif.—An extrasolar planet under three suns has been discovered in the constellation Cygnus by a planetary scientist at the California Institute of Technology using the 10-meter Keck I telescope in Hawaii. The planet is slightly larger than Jupiter and, given that it has to contend with the gravitational pull of three bodies, promises to seriously challenge our current understanding of how planets are formed.

In the July 14 issue of Nature, Maciej Konacki, a senior postdoctoral scholar in planetary science at Caltech, reports on the discovery of the Jupiter-class planet orbiting the main star of the close-triple-star system known as HD 188753. The three stars are about 149 light-years from Earth and are about as close to one another as the distance between the sun and Saturn.

In other words, a viewer there would see three bright suns in the sky. In fact, the sun that the planet orbits would be a very large object in the sky indeed, given that the planet's "year" is only three and a half days long. And it would be yellow, because the main star of HD 188753 is very similar to our own sun. The larger of the other two suns would be orange, and the smaller red.

Konacki refers to the new type of planet as "Tatooine planets," because of the similarity to Luke Skywalker's view of his home planet's sky in the first Star Wars movie.

"The environment in which this planet exists is quite spectacular," says Konacki. "With three suns, the sky view must be out of this world-literally and figuratively."

However, Konacki adds that the fact that a planet can even exist in a multiple-star system is amazing in itself. Binary and multiple stars are quite common in the solar neigborhood, and in fact outnumber single stars by some 20 percent.

Researchers have found most of the extrasolar planets discovered so far by using a precision velocity technique that is easier to employ on studies of single stars. Experts generally avoided close-binary and close-multiple stars because the existing planet detection techniques fail for such complicated systems, and also because theories of solar-system formation suggested that planets were very unlikely to form in such environments.

Konacki's breakthrough was made possible by his development of a novel method that allows him to precisely measure velocities of all members of close-binary and close-multiple-star systems. He used the technique for a search for extrasolar planets in such systems with the Keck I telescope. The planet in the HD 188753 system is the first one from this survey.

"If we believe that the same basic processes lead to the formation of planets around single stars and components of multiple stellar systems, then such processes should be equally feasible, regardless of the presence of stellar companions," Konacki says. "Planets from complicated stellar systems will put our theories of planet formation to a strict test."

Scientists in 1995 discovered the first "hot Jupiter"-in other words, an extrasolar gas-giant planet with an orbital period of three to nine days. Today, more than 20 such planets are known to orbit other stars. These planets are believed to form in a disk of gas and condensed matter at or beyond three astronomical units (three times the 93-million-mile distance between the sun and Earth).

A sufficient amount of solid material exists at three astronomical units to produce a core capable of capturing enough gas to form a giant planet. After formation, these planets are believed to migrate inward to their present very close orbits.

If the parent star is orbited by a close stellar companion, then its gravitational pull can significantly truncate a protoplanetary disk around the main star. In the case of HD 188753, the two stellar companions would truncate the disk around the main star to a radius of only 1.3 astronomical units, leaving no space for a planet to form.

"How that planet formed in such a complicated setting is very puzzling. I believe there is yet much to be learned about how giant planets are formed," says Konacki.

The research was funded by NASA.

 

 

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Robert Tindol
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Research on Sumatran Earthquakes Uncovers New Mysteries about Workings of Earth

PASADENA, Calif.--The Sumatra-Andaman earthquake of December 26 was an unmitigated human disaster. But three new papers by an international group of experts show that the huge data return could help scientists better understand extremely large earthquakes and the disastrous tsunamis that can be associated with them.

Appearing in a themed issue of this week's journal Science, the three papers are all co-authored by California Institute of Technology seismologists. The papers describe in unprecedented detail the rupture process of the magnitude-9 earthquake, the nature of the faulting, and the global oscillations that resulted when the earthquake "delivered a hammer blow to our planet." The work also shows evidence that the odd sequence of ground motions in the Andaman Islands will motivate geophysicists to further investigate the physical processes involved in earthquakes.

"For the first time it is possible to do a thorough seismological study of a magnitude-9 earthquake," says Hiroo Kanamori, who is the Smits Professor of Geophysics at Caltech and a co-author of all three papers. "Since the occurrence of similar great earthquakes in the 1960s, seismology has made good progress in instrumentation, theory, and computational methods, all of which allowed us to embark on a thorough study of this event."

"The analyses show that the Global Seismic Network, which was specifically designed to record such large earthquakes, performed exactly according to design standards," adds Jeroen Tromp, who is McMillan Professor of Geophysics and director of the Caltech Seismology Lab. "The network enables a broadband analysis of the rupture process, which means that there is considerable information over a broad range of wave frequencies, allowing us to study the earthquake in great detail.."

In fact, Kanamori points out, the data have already motivated tsunami experts to investigate how tsunamis are generated by seismic deformation. In the past, seismic deformation was treated as instantaneous uplift of the sea floor, but because of the extremely long rupture length (1200 km), slow deformation, and the large horizontal displacements as well as vertical deformation, the Sumatra-Andaman earthquake forced tsunami experts to rethink their traditional approach. Experts and public officials are now incorporating these details into modeling so that they can more effectively mitigate the human disaster of future tsunamis.

Another oddity contained in the data is the rate at which the ground moved in the Andaman Islands. Following the rapid seismic rupture, significant slip even larger than the co-seismic slip (in other words, the slip that occurred during the actual earthquake) continued beneath the islands over the next few days.

"We have never seen this kind of behavior," says Kanamori. "If slip can happen over a few days following the rapid co-seismic slip, then important hitherto unknown deformational processes in the Earth's crust must have been involved; this will be the subject of future investigations."

As for the "ringing" of Earth for literally weeks after the initial shock, the scientists say that the information will provide new insights into the planet's interior composition, mineralogy, and dynamics. In addition, the long-period free oscillations of such a large earthquake provide information on the earthquake itself.

The first of the papers is "The Great Sumatra-Andaman Earthquake of 26 December 2004. " In addition to Kanamori, the other authors are Thorne Lay (the lead author) and Steven Ward of UC Santa Cruz; Charles Ammon of Penn State; Meredith Nettles and Goan Estrom of Harvard; Richard Aster and Susan Bilek of the New Mexico Institute of Mining and Technology; Susan Beck of the University of Arizona; Michael Brudzinski of the University of Wisconsin and Miami University; Rhett Butler of the IRIS Consortium; Heather DeShon of the University of Wisconsin; Kenji Satake of the Geological Survey of Japan; and Stuart Sipkin of the US Geological Survey's National Earthquake Information Center.

The second paper is "Rupture Process of the 2004 Sumatra-Andaman Earthquake." The Caltech co-authors are Ji Chen, Sidao Ni, Vala Hjorleifsdottir, Hiroo Kanamori, and Donald Helmberger, the Smits Family Professor of Geological and Planetary Sciences.

The other authors are Charles Ammon (the lead author) of Penn State; David Robinson and Shamita Das of the University of Oxford; Thorne Lay of UC Santa Cruz; Hong-Kie Thio and Gene Ichinose of URS Corporation; Jascha Polet of the Institute for Crustal Studies; and David Wald of the National Earthquake Information Center.

The third paper is "Earth's Free Oscillations Excited by the 26 December 2004 Sumatra-Andaman Earthquake," of which Jeffrey Park of Yale University is lead author. The Caltech coauthors are Teh-Ruh Alex Song, Jeroen Tromp, and Hiroo Kanamori. The other authors are Emile Okal and Seth Stein of Northwestern University; Genevieve Roult and Eric Clevede of the Institute de Physique du Globe, Paris; Gabi Laske, Peter Davis, and Jon Berger of the Scripps Institute of Oceanography; Carla Braitenberg of the University of Trieste; Michel Van Camp of the Royal Observatory of Belgium; Xiang'e Lei, Heping Sun, and Houze Xu of the Chinese Academy of Sciences' Institute of Geodesy and Geophysics; and Severine Rosat of the National Astronomical Observatory of Japan.

The second paper contains web references to three animations that help to illustrate various aspects of this great earthquake:

http://www.gps.caltech.edu/~vala/sumatra_velocity_global.mpeg

Global movie of the vertical velocity wave field. The computation includes periods of 20 seconds and longer and shows a total duration of 3 hours. The largest amplitudes seen in this movie are the Rayleigh waves traveling around the globe. Global seismic stations are shown as yellow triangles.

http://www.gps.caltech.edu/~vala/sumatra_velocity_local.mpeg

Animation of the vertical velocity wave field in the source region. The computation includes periods of 12 seconds and longer with a total duration of about 13 minutes. As the rupture front propagates northward the wave-field gets compressed and amplified in the north and drawn out to the south. The radiation from patches of large slip shows up as circles that are offset from each other due to the rupture propagation (a Doppler-like effect).

http://www.gps.caltech.edu/~vala/sumatra_displacement_local.mpeg

Evolution of uplift and subsidence above the megathrust with time. The duration of the rupture is 550 seconds. This movie shows the history of the uplift at each point around the fault and, as a result, the dynamic part of the motion is visible (as wiggling contour lines). The simulation includes periods of 12 s and longer. The final frame of the movie shows the static field.

All animations were produced by Seismo Lab graduate student Vala Hjorleifsdottir with the assistance of Santiago Lombeyda at Caltech's Center for Advanced Computing Research. The simulations were performed on 150 nodes of Caltech's Division of Geological & Planetary Sciences' Dell cluster.

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The Science behind the Aceh Earthquake

PASADENA, Calif. - Kerry Sieh, the Robert P. Sharp Professor of Geology at the California Institute of Technology and a member of Caltech's Tectonics Observatory, has conducted extensive research on both the Sumatran fault and the Sumatran subduction zone. Below, Sieh provides scientific background and context for the December 26, 2004 earthquake that struck Aceh, Indonesia.

The earthquake that struck northern Sumatra on December 26, 2004, was the world's largest earthquake since the great (magnitude 9.2) Alaskan earthquake of 1964. The great displacements of the sea floor associated with the earthquake produced exceptionally large tsunami waves that spread death and destruction throughout the Bay of Bengal, from Northern Sumatra to Thailand, Sri Lanka, and India.

The earthquake originated along the boundary between the Indian/Australian and Eurasian tectonic plates, which arcs 5,500 kilometers (3,400 miles) from Myanmar past Sumatra and Java toward Australia see Figure 1. Near Sumatra, the Indian/Australian plate is moving north-northeast at about 60 millimeters (2.4 in.) per year with respect to Southeast Asia. The plates meet 5 kilometers (3 miles) beneath the sea at the Sumatran Trench, on the floor of the Indian Ocean Figure 2. The trench runs roughly parallel to the western coast of Sumatra, about 200 kilometers (125 miles) offshore. At the trench, the Indian/Australian plate is being subducted; that is, it is diving into the earth's interior and being overridden by Southeast Asia. The contact between the two plates is an earthquake fault, sometimes called a "megathrust." Figure 3 The two plates do not glide smoothly past each other along the megathrust but move in "stick-slip" fashion. This means that the megathrust remains locked for centuries, and then slips suddenly a few meters, generating a large earthquake.

History reveals that the subduction megathrust does not rupture all at once along the entire 5,500-kilometer plate boundary. The U.S. Geological Survey reports that the rupture began just north of Simeulue Island Figure 4. From the analysis of seismograms, Caltech seismologist Chen Ji has found that from this origin point, the major rupture propagated northward about 400 kilometers (249 miles) along the megathrust at about two kilometers per second. By contrast, the extent of major aftershocks suggests that the rupture extended about a thousand kilometers (620 miles) northward to the vicinity of the Andaman Islands. During the rupture, the plate on which Sumatra and the Andaman Islands sit lurched many meters westward over the Indian plate.

The section of the subduction megathrust that runs from Myanmar southward across the Andaman Sea, then southeastward off the west coast of Sumatra, has produced many large and destructive earthquakes in the past two centuries Figure 5. In 1833, rupture of a long segment offshore central Sumatra produced an earthquake of about magnitude 8.7 and attendant large tsunamis. In 1861, a section just north of the equator produced a magnitude 8.5 earthquake and large tsunamis. Other destructive historical earthquakes and tsunamis have been smaller. A segment to the north of the Nicobar Islands ruptured in 1881, generating an earthquake with an estimated magnitude of 7.9. A short segment farther to the south, under the Batu Islands, ruptured in 1935 (magnitude 7.7). A segment under the Enganno Island ruptured in 2000 (magnitude 7.8), and a magnitude 7.4 precursor to the recent earthquake occurred in late 2002, under Simeulue Island.

This recent earthquake was generated by the seismic rupture of only the northernmost portion of the Sumatran section of the megathrust. Therefore, the fact that most of the other part of the section has generated few great earthquakes in more than a hundred years is worrisome. Paleoseismic research has shown that seismic ruptures like the one in 1833, for example, recur about every two centuries. Thus, other parts within the section of this fault should be considered dangerous over the next few decades.

During rupture of a subduction megathrust, the portion of Southeast Asia that overlies the megathrust jumps westward (toward the trench) by several meters, and upward by 1-3 meters (3-10 feet). This raises the overlying ocean, so that there is briefly a "hill" of water about 1-3 meters high overlying the rupture. The flow of water downward from this hill triggers a series of broad ocean waves that are capable of traversing the entire Bay of Bengal. When the waves reach shallow water they slow down and increase greatly in height--up to 10 meters (32 feet) or so in the case of the December 26 earthquake--and thus are capable of inundating low-lying coastal areas.

Although the tsunami waves subside in a short period of time, some coastal areas east of the megathrust sink by a meter or so, leading to permanent swamping of previously dry, habitable ground. Islands above the megathrust rise 1 to 3 meters, so that shallow coral reefs emerge from the sea. Such long-term changes resulting from the December 26 earthquake will be mapped in the next few months by Indonesian geologists and their colleagues.

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More Stormy Weather on Titan

PASADENA, Calif.— Titan, it turns out, may be a very stormy place. In 2001, a group of astronomers led by Henry Roe, now a postdoctoral scholar at the California Institute of Technology, discovered methane clouds near the south pole of Saturn's largest moon, resolving a debate about whether such clouds exist amid the haze of its atmosphere.

Now Roe and his colleagues have found similar atmospheric disturbances at Titan's temperate mid-latitudes, about halfway between the equator and the poles. In a bit of ironic timing, the team made its discovery using two ground-based observatories, the Gemini North and Keck 2 telescopes on Mauna Kea, in Hawaii, in the months before the Cassini spacecraft arrived at Saturn and Titan. The work will appear in the January 1, 2005, issue of the Astrophysical Journal.

"We were fortunate to catch these new mid-latitude clouds when they first appeared in late 2003 and early 2004," says Roe, who is a National Science Foundation Astronomy and Astrophysics Postdoctoral Scholar at Caltech. Much of the credit goes to the resolution and sensitivity of the two ground-based telescopes and their use of adaptive optics, in which a flexible mirror rapidly compensates for the distortions caused by turbulence in the Earth's atmosphere. These distortions are what cause the well-known twinkling of the stars. Using adaptive optics, details as small as 300 kilometers across can be distinguished despite the enormous distance of Titan (1.3 billion kilometers). That's equivalent to reading an automobile license plate from 100 kilometers away.

Still to be determined, though, is the cause of the clouds. According to Chad Trujillo, a former Caltech postdoctoral scholar and now a scientist at the Gemini Observatory, Titan's weather patterns can be stable for many months, with only occasional bursts of unusual activity like these recently discovered atmospheric features.

Like Earth, Titan's atmosphere is mostly nitrogen. Unlike Earth, Titan is inhospitable to life due to the lack of atmospheric oxygen and to its extremely cold surface temperatures (-297 degrees Fahrenheit). Along with nitrogen, Titan's atmosphere also contains a significant amount of methane, which may be the cause of the mid-latitude clouds.

Conditions on Earth allow water to exist in liquid, solid, or vapor states, depending on localized temperatures and pressures. The phase changes of water between these states are an important factor in the formation of weather in our atmosphere. But on Titan, methane rules. The moon's atmosphere is so cold that any water is frozen solid, but methane can move between liquid, solid, and gaseous states. This leads to a methane meteorological cycle on Titan that is similar to the water-based weather cycle on Earth.

While the previously discovered south polar clouds are thought to be a result of solar surface heating, the new mid-latitude clouds cannot be formed by the same mechanism. One possible explanation for the new clouds is a seasonal shift in the global winds. More likely, says Roe, surface activity might be disturbing the atmosphere at the mid-latitude location. Geysers of methane slush may be brewing up from below, or a warm spot on Titan's surface may be heating the atmosphere. Cryovolcanism--volcanic activity that spews an icy mix of chemicals--is another mechanism that could cause disturbances. Hints about what is happening on this frigid world could be obtained as the Huygens probe, which will be released from Cassini on Christmas day, drops through Titan's atmosphere in January 2005.

If the clouds are being caused by these geological conditions, says Roe, they should stay at the observed 40-degree latitude and repeatedly occur above the same surface feature or features. Meanwhile, if a seasonal shift in the winds is forming the clouds then their locations should move northward as Titan's season progresses into southern summer. "Continued observations with the Gemini and Keck telescopes will easily distinguish between these two scenarios," says Roe.

The Gemini observatory is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation, involving the National Optical Astronomy Observatory, AURA, and the NSF as the U.S. partner. The W.M. Keck Observatory is operated by the California Association for Research in Astronomy, a scientific partnership between the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

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