Clouds discovered on Saturn's moon Titan

Teams of astronomers at the California Institute of Technology and at the University of California, Berkeley, have discovered methane clouds near the south pole of Titan, resolving a fierce debate about whether clouds exist amid the haze of the moon's atmosphere.

The new observations were made using the W. M. Keck II 10-meter and the Gemini North 8-meter telescopes atop Hawaii's Mauna Kea volcano in December 2001. Both telescopes are outfitted with adaptive optics that provide unprecedented detail of features not seen even by the Voyager spacecraft during its flyby of Saturn and Titan.

The results are being published by the Caltech team in the December 19 issue of Nature and by the UC Berkeley and NASA Ames team in the December 20 issue of the Astrophysical Journal.

Titan is Saturn's largest moon, larger than the planet Mercury, and is the only moon in our solar system with a thick atmosphere. Like Earth's atmosphere, the atmosphere on Titan is mostly nitrogen. Unlike Earth, Titan is inhospitable to life due to the lack of atmospheric oxygen and its extremely cold surface temperatures (-183 degrees Celsius, or -297 degrees Fahrenheit). Along with nitrogen, Titan's atmosphere contains a significant amount of methane.

Earlier spectroscopic observations hinted at the existence of clouds on Titan, but gave no clue as to their location. These early data were hotly debated, since Voyager spacecraft measurements of Titan appeared to show a calm and cloud-free atmosphere. Furthermore, previous images of Titan had failed to reveal clouds, finding only unchanging surface markings and very gradual seasonal changes in the haziness of the atmosphere.

Improvements in the resolution and sensitivity achievable with ground-based telescopes led to the present discovery. The observations used adaptive optics, in which a flexible mirror rapidly compensates for the distortions caused by turbulence in 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 at the enormous distance of Titan (1.3 billion kilometers), equivalent of reading an automobile license plate from 100 kilometers away.

The images presented by the two teams clearly show bright clouds near Titan's south pole.

"We see the intensity of the clouds varying over as little as a few hours," said post-doctoral fellow Henry Roe, lead author for the UC Berkeley group. "The clouds are constantly changing, although some persist for as long as a few days."

Titan experiences seasons much like Earth, though its year is 30 times longer due to Saturn's distant orbit from the sun. Titan is currently in the midst of southern summer, and the south pole has been in continuous sunlight for over six Earth years. The researchers believe that this fact may explain the location of the large clouds.

"These clouds appear to be similar to summer thunderstorms on Earth, but formed of methane rather than water. This is the first time we have found such a close analogy to the Earth's atmospheric water cycle in the solar system," says Antonin Bouchez, one of the Caltech researchers.

In addition to the clouds above Titan's south pole, the Keck images, like previous data, reveal the bright continent-sized feature that may be a large icy highland on Titan's surface, surrounded by linked dark regions that are possibly ethane seas or tar-covered lowlands.

"These are the most spectacular images of Titan's surface which we've seen to date," says Michael Brown, associate professor of planetary astronomy and lead author of the Caltech paper. "They are so detailed that we can almost begin to speculate about Titan's geology, if only we knew for certain what the bright and dark regions represented."

In 2004, Titan will be visited by NASA's Cassini spacecraft, which will look for clouds on Titan during its multiyear mission around Saturn. "Changes in the spatial distribution of these clouds over the next Titan season will help pin down their detailed formation process," says Imke de Pater, professor of astronomy at UC Berkeley. The Cassini mission includes a probe named Huygens that will descend by parachute into Titan's atmosphere and land on the surface near the edge of the bright continent.

The team conducting the Gemini observations consists of Roe and de Pater from UC Berkeley, Bruce A. Macintosh of Lawrence Livermore National Laboratory, and Christopher P. McKay of the NASA Ames Research Center. The team reporting results from the Keck telescope consists of Brown and Bouchez of Caltech and Caitlin A. Griffith of the University of Arizona.

The Gemini observatory is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation, involving NOAO/AURA/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. This research has been funded in part by grants from NSF and NASA.

Contact: Robert Tindol (626) 395-3631


New Theory Accounts for Existence of Binaries in Kuiper Belt

PASADENA, Calif.--In the last few years, researchers have discovered more than 500 objects in the Kuiper belt, a gigantic outer ring in the outskirts of the solar system, beyond the orbit of Neptune. Of these, seven so far have turned out to be binaries--two objects that orbit each other. The surprise is that these binaries all seem to be pairs of widely separated objects of similar size. This is surprising because more familiar pairings, such as the Earth/moon system, tend to be unequal in size and/or rather close together.

To account for these oddities, scientists from the California Institute of Technology have devised a theory of Kuiper belt binary formation. Their work is published in the December 12 issue of the journal Nature.

According to Re'em Sari, a senior research fellow at Caltech, the theory will be tested in the near future as additional observations of Kuiper belt objects are obtained and additional binaries are discovered. The other authors of the paper are Peter Goldreich, DuBridge Professor of Astrophysics and Planetary Physics at Caltech; and Yoram Lithwick, now a postdoc at UC Berkeley.

"The binaries we are more familiar with, like the Earth/moon system, resulted from collisions that ejected material," says Sari. "That material coalesced to form the smaller body. Then the interaction between the spin of the larger body and the orbit of the smaller body caused them to move farther and farther apart."

"This doesn't work for the Kuiper belt binaries," Sari says. "They are too far away from each other to have ever had enough spin for this effect to take place." The members of the seven binaries are about 100 kilometers in radius, but 10,000 to 100,000 kilometers from each other. Thus their separations are 100 to 1,000 times their radii. By contrast, Earth is about 400,000 kilometers from the moon, and about 6,000 kilometers in radius. Even at a distance of 60 times the radius of Earth, the tidal mechanism works only because the moon is so much less massive than Earth.

Sari and his colleagues think the explanation is that the Kuiper belt bodies tend to get closer together as time goes on -- exactly the reverse of the situation with the planets and their satellites, where the separations tend to increase. "The Earth/moon system evolves 'inside-out', but the Kuiper belt binaries evolved 'outside-in,'" explains Sari.

Individual objects in the Kuiper belt are thought to have formed in the early solar system by accretion of smaller objects. The region where the gravitational influence of a body dominates over the tidal forces of the sun is known as its Hill sphere. For a 100-kilometer body located in the Kuiper belt, this extends to about a million kilometers. Large bodies can accidentally pass through one another's Hill spheres. Such encounters last a couple of centuries and, if no additional process is involved, the "transient binary" dissolves, and the two objects continue on separate orbits around the sun. The transient binary must lose energy to become bound. The researchers estimate that in about 1 in 300 encounters, a third large body would have absorbed some of the energy and left a bound binary. An additional mechanism for energy loss is gravitational interaction with the sea of small bodies from which the large bodies were accreting. This interaction slows down the large bodies. Once in every 30 encounters, they slowed down sufficiently to become bound.

Starting with a binary of large separation a million kilometers apart, continued interaction with the sea of small objects would have led to additional loss of energy, tightening the binary. The time required for the formation of individual objects is sufficient for a binary orbit to shrink all the way to contact. Indeed, the research predicts that most binaries coalesced in this manner or at least became very tight. But if the binary system was formed relatively late, close to the time that accretion in the Kuiper belt ceased, a widely separated binary would survive. These are the objects we observe today. By this mechanism it can be predicted that about 5 percent of objects remain with large enough separation to be observed as a binary. The prediction is in agreement with recent surveys conducted by Caltech associate professor of planetary astronomy Mike Brown. The majority of objects ended up as tighter binaries. Their images cannot be distinguished from those of isolated objects when observed from Earth using existing instruments.

These ideas will be more thoroughly tested as additional objects are discovered and further data is collected. Further theoretical work could predict how the inclination of a binary orbit, relative to the plane of the solar system, evolves as the orbit shrinks. If it increases, this would suggest that the Pluto/Charon system, although tight, was also formed by the 'outside-in' mechanism, since it is known to have large inclination.

Robert Tindol

Caltech Professor to Explore Abrupt Climate Changes

PASADENA, Calif.—By analyzing stalagmites from caves in Sarawak, which is the Malaysian section of Borneo and the location of one of the world's oldest rain forests, and by studying deep-sea corals from the North Atlantic Ocean, California Institute of Technology researcher Jess Adkins will explore the vital link between the deep ocean, the atmosphere, and abrupt changes in global climates.

The project, "Linking the Atmosphere and the Deep Ocean during Abrupt Climate Changes," is funded by the Comer Science and Educational Foundation.

Because the Sarawak stalagmites and the deep-sea corals are uranium rich and can be dated precisely, and because they both accumulate continuously, uninterrupted by "bioturbation," the biological process that mixes the upper several centimeters of ocean sediments, they provide unique archives of climate history. By utilizing these archives, Adkins and his research group will be able to chart and link major climate variables, and thereby provide critical insight into understanding rapid climate changes that could impact the earth.

Adkins, an assistant professor of geochemistry and global environmental science, joined Caltech in 2000. He received his PhD in 1998 from the Massachusetts Institute of Technology Woods Hole Oceanographic Institute.

The Comer Science and Education Foundation was established to promote education and discovery through scientific exploration.

Contact: Deborah Williams-Hedges (626) 395-3227

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New study describes workings of deep oceanduring the Last Glacial Maximum

Scientists know quite a bit about surface conditions during the Last Glacial Maximum (LGM), a period that peaked about 18,000 years ago, when ice covered significant portions of Canada and northern Europe.

But to really understand the mechanisms involved in climate change, scientists need to have detailed knowledge of the interaction between the ocean and the atmosphere. And until now, a key component of that knowledge has been lacking for the LGM because of limited understanding of the glacial deep ocean.

In a paper published in the November 29 issue of the journal Science, researchers from the California Institute of Technology and Harvard University report the first measurements for the temperature-salinity distribution of the glacial deep ocean. The results show unexpectedly that the basic mechanism of the distribution was different during icy times.

"You can think of the global ocean as a big bathtub, with the densest water at bottom and the lightest at top," explains Jess Adkins, an assistant professor of geochemistry and global environmental science at Caltech and lead author of the paper. Because water that is cold or salty--or both--is dense, it tends to flow downward in a vertical circulation pattern, much like water falling down the sides of the bathtub, until it finds its correct density level. In the ocean today, this circulation mechanism tends to be dominated by the temperature of the water.

In studying chlorine data from four ocean drilling program sites, the researchers found that the glacial deep ocean's circulation was set by the salinity of the water. In addition, a person walking on the ocean bottom from north to south, 18,000 years ago, would have found that the water tended to get saltier as he proceeded (within an acceptable margin of error, both north and south waters were the same temperature). Taking that into account, the water in the north would have been less dense. The exact reverse is true today, with the waters at low southern latitudes being very cold and relatively fresh, while those in the high northern latitudes being warmer and saltier.

Adkins says there is a good explanation for the change. The seawater "equation of state" dictates that the density of water near the freezing point is about two-to-three times more sensitive to changes in salinity relative to changes in temperature, as compared to today's warmer deep waters.

So, the equation demands that the density-layering of the ocean "bathtub" be set by the water's salt content at the last glacial maximum. Temperature is still crucial, in that colder waters are more sensitive to salinity changes than warmer water, but Adkin's results show that the deep water circulation mechanism must have operated in a fundamentally different manner in the past.

"This observation of the deep ocean seems like a strange place to go to study Earth's climate, but this is where you find most of the mass and thermal inertia of the climate system," Adkins says.

The ocean's water temperature enters into the complex mechanism affecting the climate, with water moving about in order for the ocean to equalize its temperature. Too, the water and air interact to further complicate the weather equation.

Thus, the results from the glacial deep ocean shows that the climate in those days was operating in a very different way, Adkins says. "Basically, the purpose of this study is to understand the mechanisms of climate change."

In addition to Adkins, the other authors are Katherine McIntyre, a postdoctoral scholar in geochemistry at Caltech; and Daniel P. Schrag of the Department of Earth and Planetary Sciences at Harvard University.

Contact: Robert Tindol (626) 395-3631


Rupture of Denali fault responsible for 7.9-magAlaskan earthquake of November 3

Geologists just back from a reconnaissance of the 7.9-magnitude Alaska earthquake of November 3 confirm that rupture of the Denali fault was the principal cause of the quake.

According to Caltech geology professor Kerry Sieh, Central Washington University geological sciences professor Charles Rubin, and Peter Haeussler of the U.S. Geological Survey, investigations over a week-long period revealed three large ruptures with a total length of about 320 kilometers. The principal rupture was a 210-kilometer-long section of the Denali fault, with horizontal shifts of up to nearly 9 meters (26 feet). This places the rupture in the same class as those that produced the San Andreas fault's two historical great earthquakes in 1906 and 1857. These three ruptures are the largest such events in the Western Hemisphere in at least the past 150 years.

Like California's San Andreas, the Denali is a strike-slip fault, which means that the blocks on either side of the fracture move sideways relative to one another. Over millions of years, the cumulative effect of tens of thousands of large shifts has been to move southern Alaska tens of kilometers westward relative to the rest of the state. These shifts have produced a set of large aligned valleys that arch through the middle of the snowy Alaska range, from the Canadian border on the east to the foot of Mount McKinley on the west. Along much of its length the great fracture traverses large glaciers. Surprisingly, the fault broke up through the glaciers, offsetting large crevasses and rocky ridges within the ice.

At the crossing of the Trans-Alaska pipeline, approximately in the center of the 320-kilometer rupture, the horizontal shift was about 4 meters. Fortunately, geological studies of the fault prior to construction led to a special design that would have allowed for shifts greater than this without failure of the pipeline.

The earthquake shook loose thousands of snow avalanches and rock falls in the rugged terrain adjacent to the fault. Although most of these measured only a few tens of meters in dimension, many were much larger. In some places enormous blocks of rock and ice fell onto glaciers and valley floors, skidding a kilometer or more out over ice, stream, and tundra.

The team of investigators included geologists from several organizations, including Caltech's Division of Geological and Planetary Sciences, the U.S. Geological Survey, Central Washington University, and the University of Alaska. The rugged range is traversed by just two highways, and so the scientists used helicopters to access the fault ruptures in the remote and rugged terrain.

Before departing for the field, the geologists had learned from seismologists the basic character of the rupture. Within a day of the quake, Caltech seismologist Chen Ji had determined that the shift along the fault was principally horizontal, but that the initial 20 seconds of the eastward-propagating crack was along a fault with vertical motion. This fault was discovered midweek, near the western end of the principal horizontal shift. Along this 40-kilometer-long fault, a portion of the Alaska range has risen several meters.

Perhaps the most surprising discovery in the field was that the fault rupture propagated only eastward from the epicenter and left the western half of the great fault unbroken. Several members of the team wonder if, in fact, this great earthquake is the first in a series of large events that will eventually include breaks farther west toward Mount McKinley and Denali National Park.

Contact: Robert Tindol (626) 395-3631


Caltech scientists find largest object in solar system since Pluto's discovery

Planetary scientists at the California Institute of Technology have discovered a spherical body in the outskirts of the solar system. The object circles the sun every 288 years, is half the size of Pluto, and is larger than all of the objects in the asteroid belt combined.

The object has been named "Quaoar" (pronounced KWAH-o-ar) after the creation force of the Tongva tribe who were the original inhabitants of the Los Angeles basin, where the Caltech campus is located. Quaoar is located about 4 billion miles from Earth in a region beyond the orbit of Pluto known as the Kuiper belt. This is the region where comets originate and also where planetary scientists have long expected to eventually find larger planet-shaped objects such as Quaoar. The discovery, announced at the meeting of the Division of Planetary Sciences of the American Astronomical Society in Birmingham, Alabama, today, is by far the largest object found so far in that search.

Currently detectable a few degrees northwest of the constellation Scorpio, Quaoar demonstrates beyond a doubt that large bodies can indeed be found in the farthest reaches of the solar system. Further, the discovery provides hope that additional large bodies in the Kuiper belt will be discovered, some as large, or even larger than Pluto. Also, Quaoar and other bodies like it should provide new insights into the primordial materials that formed the solar system some 5 billion years ago.

The discovery further supports the ever-growing opinion that Pluto itself is a Kuiper belt object. According to recent interpretations, Pluto was the first Kuiper belt object to be discovered, long before the age of enhanced digital techniques and charge-coupled (CCD) cameras, because it had been kicked into a Neptune-crossing elliptical orbit eons ago.

"Quaoar definitely hurts the case for Pluto being a planet," says Caltech planetary science associate professor Mike Brown. "If Pluto were discovered today, no one would even consider calling it a planet because it's clearly a Kuiper belt object."

Brown and Chad Trujillo, a postdoctoral researcher, first detected Quaoar on a digital sky image taken on June 4 with Palomar Observatory's 48-inch Oschin Telescope. The researchers looked through archived images taken by a variety of instruments and soon found images taken in the years 1983, 1996, 2000, and 2001. These images not only allowed Brown and Trujillo to establish the distance and orbital inclination of Quaoar, but also to determine that the body is revolving around the sun in a remarkably stable, circular orbit.

"It's probably been in this same orbit for 4 billion years," Brown says.

The discovery of Quaoar is not so much a triumph of advanced optics as of modern digital analysis and a deliberate search methodology. In fact, Quaoar apparently was first photographed in 1982 by then-Caltech astronomer Charlie Kowal in a search for the postulated "Planet X." Kowal unfortunately never found the object on the plate—much less Planet X—but left the image for posterity.

Because the precise location of Quaoar on the old plates is highly predictable, the orbit is thought to be quite circular for a solar system body, and far more circular than that of Pluto. In fact, Pluto is relatively easy to spot—at least if one knows where to look. Because Pluto comes so close to the sun for several years in its 248-year eccentric orbit, the volatile substances in the atmosphere are periodically heated, thereby increasing the body's reflectance, or albedo, to such a degree that it is bright enough to be seen even in small amateur telescopes.

Quaoar, on the other hand, never approaches the sun in its circular orbit, which means that the volatile gases never are excited enough to kick up a highly reflective atmosphere. As is the case for other bodies of similar rock-and-ice composition, Quaoar's surface has been bathed by faint ultraviolet radiation from the sun over the eons, and this radiation has slowly caused the organic materials on the body's surface to turn into a dark tar-like substance.

As a result, Quaoar's albedo is about 10 percent, just a bit higher than that of the moon. By contrast, Pluto's albedo is 60 percent.

As for spin rate, the researchers know that Quaoar is rotating because of slight variations in reflectance in the six weeks they've observed the body. But they're still collecting data to determine the precise rate. They will also probably be able to figure out whether the spin axis is tilted relative to the ecliptical plane.

Inclination is about 7.9 percent, which means that the plane of Quaoar's orbit is tilted by 7.9 degrees from the relatively flat orbital plane in which all the planets except Pluto are to be found. Pluto's orbital inclination is about 17 degrees, which presumably resulted from whatever gravitational interference originally thrust it into an elliptical orbit.

Quaoar's orbital inclination of 7.9 degrees is not particularly surprising, Brown says, because the Kuiper belt is turning out to be wider than originally expected. The Kuiper belt can be thought of as a band extending around the sky, superimposed on the path of the sun. Brown and Trujillo's research, in effect, is to take repeated exposures of a several-degree swath of this band and then use digital equipment to check and see if any tiny point of light has moved relative to the stellar background.

Brown and Trujillo are currently using about 10 to 20 percent of the available time on the 48-inch Oschin Telescope, which was used to obtain both the Palomar Sky Survey and the more recent Palomar Digital Sky Survey. The latter was completed just last year, thus freeing up the Oschin Telescope to be refitted by the Jet Propulsion Laboratory for a new mission to search for near-Earth asteroids. About 80 percent of the telescope time is now designated for the asteroid survey, leaving the remainder for scientific studies like Brown and Trujillo's.

Since the discovery, the researchers have also employed other telescopes to study and characterize Quaoar, including the Hubble Space Telescope (related news release available at link below) and the Keck Observatory on Mauna Kea, Hawaii. Information derived from these studies will provide new insights into the precise composition of Quaoar and may answer questions about whether the body has a tenuous atmosphere.

But the good news for the serious amateur astronomer is that he or she doesn't necessarily need a space telescope or 10-meter reflector to get a faint image of Quaoar. Armed with precise coordinates and a 16-inch telescope fitted with a CCD camera—the kind advertised in magazines such as Sky and Telescope and Astronomy—an amateur should be able to obtain images on successive nights that will show a faint dot of light in slightly different positions.

As for Brown and Trujillo, the two are continuing their search for other large Kuiper-belt bodies. Some, in fact, may be even larger than Quaoar.

"Right now, I'd say they get as big as Pluto," says Brown.



MacArthur Foundation certifies two Caltech professors as geniuses

Two members of the California Institute of Technology faculty have been named MacArthur Fellows, a prestigious honor bestowed each year on innovators in a variety of fields and commonly known as the "genius grants."

Charles Steidel, an astronomer, and Paul Wennberg, an atmospheric scientist, are two of the 24 MacArthur Fellows announced today by the John D. and Catherine T. MacArthur Foundation of Chicago. Each of the 24 recipients will receive a $500,000 "no strings attached" grant over the next five years.

Steidel's expertise is cosmology, a field to which he has made numerous contributions in the ongoing attempt to understand the formation and evolution of galaxies and the development of large-scale structure in the universe. In particular, Steidel is known for the development of a technique that effectively locates early galaxies at prescribed cosmic epochs, allowing for the study of large samples of galaxies in the early universe.

Access to these large samples, which are observed primarily using the Keck telescopes on Mauna Kea on the Big Island of Hawaii, allows for the mapping of the distribution of the galaxies in space and for detailed observations of many individual galaxies. These are providing insights into the process of galaxy formation when the universe was only 10 to 20 percent of its current age.

Steidel says he hasn't yet decided what to do with the grant money. "I'm giving it some thought, but I'm still in the disbelief phase—it took me completely by surprise!" he said.

"The unique nature of the fellowship makes me feel like I should put a great deal of thought into coming up with a creative use for the money. It does feel a bit odd to be recognized for work that is by its nature collaborative and dependent on the hard work of many people, but at the same time I am very excited by the possibilities!"

A graduate of Princeton University and the California Institute of Technology, Steidel was a faculty member at MIT before returning to Caltech, where he is now a professor of astronomy. He is also a past recipient of fellowships from the Sloan and Packard foundations, and received a Young Investigator Award from the National Science Foundation in 1994. In 1997 he was presented the Helen B. Warner Prize by the American Astronomical Society for his significant early-career contributions to astronomy.

Wennberg holds joint appointments as a professor of atmospheric chemistry and a professor of environmental science and engineering. A specialist in how both natural and human processes affect the atmosphere, Wennberg is particularly interested in measuring a class of substances known as radicals and how they enter into atmospheric chemical reactions. These radicals are implicated in processes that govern the health of the ozone layer as well as the presence of greenhouse gases.

Wennberg has earned recognition in the field for developing airborne sensors to study radicals and their chemistry. One of the early scientific results from these measurements demonstrated that conventional thinking was incorrect about how ozone is destroyed in the lower stratosphere, affecting assessments of the environmental impacts of chlorofluorocarbons and stratospheric aircraft.

Wennberg said he was "blown over by the award" when he received notification. "It is a wonderful recognition of the work that I have done in association with the atmospheric scientists working on NASA's U-2 aircraft chemistry program."

"I have been pondering how I might use the funds, but have no concrete plans at the moment. It will certainly enable me to do things I wouldn't have thought possible—perhaps even take up the bassoon again! "

A graduate of Oberlin College and Harvard University, Wennberg was a research associate at Harvard before joining the Caltech faculty. In 1999 he was named recipient of a Presidential Early Career Award in Science and Engineering.


Caltech geophysicists find four active volcanoes in Andes with innovative satellite radar survey

Four volcanoes in the central Andes mountains of South America, all previously thought to be dormant, must now be considered active due to ground motions detected from space, geophysicists say.

In a paper appearing in the July 11 issue of the journal "Nature", California Institute of Technology geophysics graduate student Matt Pritchard and his faculty adviser, Mark Simons, unveil their analysis of eight years of radar interferometry data taken on 900 volcanoes in the Andes. The data were gathered from 1992 to 2000 by the European Space Agency's two remote-sensing satellites, ERS 1 and ERS 2.

Of the four centers of activity, Hualca Hualca volcano in southern Peru is especially worth close observation because of the population density in the area and because it is just a few miles from the active Sabancaya volcano. A second volcano now shown to be active, Uturuncu in Bolivia, is bulging vertically about 1-to-2 centimeters per year, according to the satellite data, while a third, Robledo caldera in Argentina, is actually deflating for unknown reasons. A fourth region of surface deformation, on the border between Chile and Argentina, was unknown prior to the study, so the authors christened it "Lazufre" because it lies between the two volcanoes Lastarria and Cordon del Azufre.

While the study provides important new information about volcanic hazards in its own right, Pritchard, the lead author, says it also proves the mettle of a new means of studying ground deformation that should turn out to be vastly superior to field studies. The fact that none of the four volcanoes were known to be active—and thus probably wouldn't have been of interest to geophysicists conducting studies using conventional methods—shows the promise of the technique, he says.

"Achieving this synoptic perspective would have been an impractical undertaking with ground-based methods, like the GPS system," Pritchard says.

The sensitive data is superior to ground-based results in that a huge amount of subtle information can be accumulated about a large number of geological features. The satellites bounce a radar signal off the ground, and then accurately measure the time it takes the signal to return. On a later pass, when the satellite is again in approximately the same spot, it sends another signal to the ground.

If the two signals are out of phase, then the distance from the satellite to the ground is either increasing or decreasing, and if the features are volcanic, then the motion can be assumed to have been caused by movement of magma in the subsurface or by hydrothermal activity.

"You can think of a magma chamber as a balloon beneath the surface inflating and deflating. So if the magma is building up underground, you expect a swelling upward, and this is what we can detect with the satellite data."

Given the appropriate satellite mission, all the world's subaerial volcanoes could be easily monitored for active deformation on a weekly basis. Such a capability would have a profound impact on minimizing volcanic hazards in regions lacking necessary infrastructure for regular geophysical monitoring.

Another unusual finding from the study that shows its promise in better understanding volcanism is the Lascar volcano's lack of motion. Lascar has had three major eruptions since 1993, as well as several minor ones, and many volcanologists assume there should have been some ground swelling over the years of the study, Pritchard says.

"But we find no deformation at the volcano," he explains. "Some people find it curious, others think it's not unexpected. But it's a new result, and regardless of what's going on, it could tell us interesting things about magma plumbing."

There are several possible explanations to account for the lack of vertical motion at the Lascar volcano, Pritchard says. The first and most obvious is that the satellite passes took place at times between inflations and subsequent deflations, so that no net ground motion was recorded. It could also be that magma is somehow able to get from within Earth to the atmosphere without deforming surfaces at all; or that a magma chamber might be deep enough to allow an eruption without surface deformations being visible, even though deformation is occurring at depth.

The study is also noteworthy in that Simons and Pritchard were able to do their work without leaving their offices on the Caltech campus. The data analysis was done with software developed at Caltech and the Jet Propulsion Laboratory, and the authors say this software was critical to the study's success.

Simons, an assistant professor of geophysics at Caltech, and Pritchard are scheduled to attend a geophysics conference in Chile in October, and will try to see some or all of the four volcanoes at that time.

Contact: Robert Tindol (626) 395-3631


Geophysicists Find Sharp-Sides to the African Superplume

Scientists at the California Institute of Technology have discovered that the African superplume-a massive, hot upwelling of rock beneath southern Africa-has edges that are sharp and distinct, not diffuse and blurred as previously thought. Such sharp, lateral boundaries have never been found in the Earth's mantle before, and they challenge scientist's understanding of the interior.

In a paper to be published in the June 7 issue of the journal Science, a team of geophysicists at Caltech's Seismological Laboratory used a fortuitous set of seismic waves from distant earthquakes to show that the boundary of the African superplume appears to be sharp, with a width of about 30 miles. The sharp boundary is not vertical but somewhat tilted, somewhat like a rising plume of smoke that is tilted by the wind. This suggests that the plume is unstable. Using dynamic computer modeling, the scientists provide further evidence of what they and other geologists suspected, that the superplume has a dense chemical core that differs from the scalding hot rock that comprises the surrounding mantle.

The team of scientists from Caltech includes Sidao Ni, the paper's lead author and a staff scientist in the seismology lab; graduate student Eh Tan; Michael Gurnis, professor of geophysics; and Don Helmberger, the Smits Family Professor of Geophysics and Planetary Science and director of the Caltech seismology lab.

About 20 years ago, scientists developed a way to make three-dimensional "snapshots" of the earth's interior using the seismic waves, or vibrations, that travel through the earth following an earthquake. By measuring the time it takes for these waves to travel from an earthquake's epicenter to a recording station, they can infer the temperatures and densities in a given segment of the mantle, the middle layer of the earth. In the mid-1980s, they noticed a huge area under Africa where seismic waves passed through slowly implying that the solid rock was at a substantially higher temperature.

Some 750 miles across and more than 900 miles tall, the region was initially thought to be a giant anomaly, with broad, diffuse edges, that was hotter than the mantle's surrounding rock. The so-called African superplume was slowly rising upwards, much like the thermal convection that occurs in a pot of boiling water. As seismic instrumentation improved, other evidence suggested that the structure might be more than thermal, possibly having a different chemical composition from the surrounding mantle rock.

If there were heavy and dense material associated with this anomalous mantle, the scientists reasoned, then it would either lie underneath or within the vast majority of the hot, rising African superplume. "So we said if that's the case, there should actually be a sharp boundary between the two materials, instead of a diffuse boundary," says Gurnis. The researchers went looking.

By pure chance, other unrelated work had placed a series of seismic detectors in southern Africa. This allowed the Caltech team to study and interpret the fine-scale structure of earthquake seismic waves recorded by the arrays. The energy from the earthquakes emanated from South America and passed through the African superplume.

It turned out, says Gurnis, that a clear pattern of waves developed that grazed the east edge of the plume, creating a peculiar pattern that was indicative of being an incredibly sharp boundary-a boundary that probably extends nearly 900 miles above the core. The findings startled the researchers. "No one expected this," says Gurnis. "Everybody thought there'd be these very broad, diffuse structures. Instead what we've found is a structure that is much bigger, much sharper, and extends further off the core mantle boundary."

They also found that the structure, instead of having a dome-like appearance predicted by their computer models, tilts toward the northeast. Gurnis speculates that's probably due to its dynamic state-"It's a completely different observation from what we expected to see," he says.

At this point, the team can only speculate on the causes. "One of the ideas, and it's not perfect, is that the rock composition of the plume is more iron rich, and thus denser," Gurnis suggests. "It will be interesting to see what observations other scientists can make. The idea of sharp, near-vertical edges was not on people's agendas before now, so this may change people's perspectives on the interior.

"I don't particularly like this idea," Gurnis admits; "it's strange. I guess that's why we find it so interesting."

The interdisciplinary team of researchers was funded by the National Science Foundation's Cooperative Studies of Earth's Deep Interior program.


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Researchers find new clue why Martian wateris found on the north pole, not the south

When astronauts finally land on Mars, a safe bet is that they'll head for northern climes if they intend to spend much time there. That's because nearly all the available water is frozen as ice at the north pole. Planetary scientists have been aware of this for some time, but they now have a new clue why it is so.

In the March 21 issue of the journal Nature, California Institute of Technology researcher Mark Richardson and his colleague John Wilson of the National Oceanic and Atmospheric Administration reveal that the higher average elevation of the Red Planet's southern hemisphere ultimately tends to drive water northward.

Their evidence is based on a computer model the two have worked on for years (Wilson since 1992, Richardson since 1996), coupled with data returned by NASA's Mars Global Surveyor.

"We've found a mechanism in the Martian climate that introduces annual average hemispheric asymmetry," explains Richardson, an assistant professor of planetary science at Caltech. "The circulation systems of Mars and Earth are similar in certain ways, but Mars is different in that water is not available everywhere."

The key to understanding the phenomenon is a complicated computer modeling of the Hadley circulation, which extends about 40 degrees of latitude each side of the Martian equator. A topographical bias in circulation pretty much means there will be a bias in the net pole-to-pole transport of water, Richardson explains.

A plausible explanation is that water ice is found at the north pole and carbon dioxide ice is found at the south for reasons having to do with the way the sun heats the atmosphere. As the Martian orbit changes on time scales of 50,000 years and more, these effects tend to cancel, with no pole claiming the water ice cap over geological time. It has been suggested that topography determines where carbon dioxide forms, and hence, where water ice can form, but the processes controlling carbon dioxide ice caps are poorly understood.

However, the mechanism Richardson and Wilson describe is independent of this occasional realignment of the pole's precession and the planet's eccentric orbit. The mechanism means that, while there is never a time in the past when water ice can be discounted at the south pole, one is more likely to find it more frequently at the north pole.

The importance of the study is its furthering of our understanding of the Martian climate and Martian water cycle. A better understanding of how water is transported will be particularly important to determining whether life once existed on Mars, and what happened to it if it ever did.

The Web address for the journal Nature is

Contact: Robert Tindol (626) 395-3631



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