Study of 2004 Tsunami Disaster Forces Rethinking of Theory of Giant Earthquakes

PASADENA, Calif.—The Sumatra-Andaman earthquake of December 26, 2004, was one of the worst natural disasters in recent memory, mostly on account of the devastating tsunami that followed it. A group of geologists and geophysicists, including scientists at the California Institute of Technology, has delineated the full dimensions of the fault rupture that caused the earthquake.

Their findings, reported in the March 2 issue of the journal Nature, suggest that previous ideas about where giant earthquakes are likely to occur need to be revised. Regions of the earth previously thought to be immune to such events may actually be at high risk of experiencing them.

Like all giant earthquakes, the 2004 event occurred on a subduction megathrust-in this case, the Sunda megathrust, a giant earthquake fault, along which the Indian and Australian tectonic plates are diving beneath the margin of southeast Asia. The fault surface that ruptured cannot be seen directly because it lies several kilometers deep in the Earth's crust, largely beneath the sea.

Nevertheless, the rupture of the fault caused movements at the surface as long-accumulating elastic strain was suddenly released. The researchers measured these surface motions by three different techniques. In one, they measured the shift in position of GPS stations whose locations had been accurately determined prior to the earthquake.

In the second method, they studied giant coral heads on island reefs: the top surfaces of these corals normally lie right at the water surface, so the presence of corals with tops above or below the water level indicated that the Earth's crust rose or fell by that amount during the earthquake.

Finally, the researchers compared satellite images of island lagoons and reefs taken before and after the earthquake: changes in the color of the seawater or reefs indicated a change in the water's depth and hence a rise or fall of the crust at that location.

On the basis of these measurements the researchers found that the 2004 earthquake was caused by rupture of a 1,600-kilometer-long stretch of the megathrust-by far the longest of any recorded earthquake. The breadth of the contact surface that ruptured ranged up to 150 kilometers. Over this huge contact area, the surfaces of the two plates slid against each other by up to 18 meters.

On the basis of these data, the researchers calculated that the so-called moment-magnitude of the earthquake (a measure of the total energy released) was 9.15, making it the third largest earthquake of the past 100 years and the largest yet recorded in the few decades of modern instrumentation.

"This earthquake didn't just break all the records, it also broke some of the rules," says Kerry Sieh, who is the Sharp Professor of Geology at Caltech and one of the authors of the Nature paper.

According to previous understanding, subduction megathrusts can only produce giant earthquakes if the oceanic plate is young and buoyant, so that it locks tightly against the overriding continental plate and resists rupture until an enormous amount of strain has accumulated.

Another commonly accepted idea is that the rate of relative motion between the colliding plates must be high for a giant earthquake to occur. Both these conditions are true off the southern coast of Chile, where the largest earthquake of the past century occurred in 1960. They are also true off the Pacific Northwest of the United States, where a giant earthquake occurred in 1700 and where another may occur before long.

But at the site of the 2004 Sumatra-Andaman earthquake the oceanic crust is old and dense, and the relative motion between the plates is quite slow. Yet another factor that should have lessened the likelihood of a giant earthquake in the Indian Ocean is the fact that the oceanic crust is being stretched by formation of a so-called back-arc basin off the continental margin.

"For all these reasons, received wisdom said that the giant 2004 earthquake should not have occurred," says Jean-Philippe Avouac, a Caltech professor of geology, who is also a contributor to the paper. "But it did, so received wisdom must be wrong. It may be, for example, that a slow rate of motion between the plates simply causes the giant earthquakes to occur less often, so we didn't happen to have seen any in recent times-until 2004."

Many subduction zones that were not considered to be at risk of causing giant earthquakes may need to be reassessed as a result of the 2004 disaster. "For example, the Ryukyu Islands between Taiwan and Japan are in an area where a large rupture would probably cause a tsunami that would kill a lot of people along the Chinese coast," says Sieh.

"And in the Caribbean, it could well be an error to assume that the entire subduction zone from Trinidad to Barbados and Puerto Rico is aseismic. The message of the 2004 earthquake to the world is that you shouldn't assume that your subduction zone, even though it's quiet, is incapable of generating great earthquakes."

According to Sieh, it's not that all subduction zones should now be assigned a high risk of giant earthquakes, but that better monitoring systems-networks of continuously recording GPS stations, for example-should be put in place to assess their seismic potential.

"For most subduction zones, a $1 million GPS system would be adequate," says Sieh. "This is a small price to pay to assess the level of hazard and to monitor subduction zones with the potential to produce a calamity like the Sumatra-Andaman earthquake and tsunami. Caltech's Tectonics Observatory has, for example, begun to monitor the northern coast of Chile, where a giant earthquake last occurred in 1877."

In addition to Sieh and Avouac, the other authors of the Nature paper are Cecep Subarya of the National Coordinating Agency for Surveys and Mapping in Cibinong, Indonesia; Mohamed Chlieh and Aron Meltzner, both of Caltech's Tectonics Observatory; Linette Prawirodirdjo and Yehuda Bock, both of the Scripps Institution of Oceanography; Danny Natawidjaja of the Indonesian Institute of Sciences; and Robert McCaffrey of Rensselaer Polytechnic Institute.

 

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Watson Lecture: The 10th Planet

PASADENA, Calif.- In 2005, after seven years scanning half the sky for planets in our solar system beyond Pluto and discovering dozens of large new objects, Michael E. Brown and his colleagues finally found 2003 UB313, aka "Xena," the first object larger than Pluto, and the first that might be called a new planet.

The discovery of 2003 UB313 inspired "a new avalanche of scientific questions," says Brown, professor of planetary astronomy at the California Institute of Technology. Perhaps more importantly for planetary science, it forced into the spotlight the lingering debate over what constitutes a planet.

On Wednesday, February 22, Brown will discuss the discovery of 2003 UB313 and the planet controversy. "By the end of the talk, listeners will know if 2003 UB313 is a planet, what a planet is and how to find one, and how many more planets might be hiding out there," he says. His talk, "Beyond Pluto: Discovery of the 10th Planet," is the first program of the Winter/Spring 2006 Earnest C. Watson Lecture Series.

The talk will take place at 8 p.m. in Beckman Auditorium, 332 S. Michigan Avenue south of Del Mar Boulevard, on the Caltech campus in Pasadena. Seating is available on a free, no-ticket-required, first-come, first-served basis. Caltech has offered the Watson Lecture Series since 1922, when it was conceived by the late Caltech physicist Earnest Watson as a way to explain science to the local community.

Upcoming lectures in the Winter/Spring 2006 series include

o Dianne K. Newman, associate professor of geobiology and environmental science and engineering, Caltech, and investigator at the Howard Hughes Medical Institute, on "Bacterial Biofilms: Far More Than a Collection of Germs," April 12.

o R. Preston McAfee, J. Stanley Johnson Professor of Business Economics and Management and Executive Officer for the Social Sciences, Caltech, on "Why Are Prices So Bizarre?," May 3.

o Paul H. Patterson, Anne P. and Benjamin F. Biaggini Professor of Biological Sciences, Caltech, on "Can One Make a Mouse Model of Mental Illness, and Why Try?," May 17.

For more information, call 1(888) 2CALTECH (1-888-222-5832) or (626) 395-4652.

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

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

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Dust Found in Earth Sediment Traced to Breakup of the Asteroid Veritas 8.2 Million Years Ago

PASADENA, Calif.—In a new study that provides a novel way of looking at our solar system's past, a group of planetary scientists and geochemists announce that they have found evidence on Earth of an asteroid breakup or collision that occurred 8.2 million years ago.

Reporting in the January 19 issue of the journal Nature, scientists from the California Institute of Technology, the Southwest Research Institute (SwRI), and Charles University in the Czech Republic show that core samples from oceanic sediment are consistent with computer simulations of the breakup of a 100-mile-wide body in the asteroid belt between Mars and Jupiter. The larger fragments of this asteroid are still orbiting the asteroid belt, and their hypothetical source has been known for years as the asteroid "Veritas."

Ken Farley of Caltech discovered a spike in a rare isotope known as helium 3 that began 8.2 million years ago and gradually decreased over the next 1.5 million years. This information suggests that Earth must have been dusted with an extraterrestrial source.

"The helium 3 spike found in these sediments is the smoking gun that something quite dramatic happened to the interplanetary dust population 8.2 million years ago," says Farley, the Keck Foundation Professor of Geochemistry at Caltech and chair of the Division of Geological and Planetary Sciences. "It's one of the biggest dust events of the last 80 million years."

Interplanetary dust is composed of bits of rock from a few to several hundred microns in diameter produced by asteroid collisions or ejected from comets. Interplanetary dust migrates toward the sun, and en route some of this dust is captured by the Earth's gravitational field and deposited on its surface.

Presently, more than 20,000 tons of this material accumulates on Earth each year, but the accretion rate should fluctuate with the level of asteroid collisions and changes in the number of active comets. By looking at ancient sediments that include both interplanetary dust and ordinary terrestrial sediment, the researchers for the first time have been able to detect major dust-producing solar system events of the past.

Because interplanetary dust particles are so small and rare in sediment-significantly less than a part per million-they are difficult to detect using direct measurements. However, these particles are extremely rich in helium 3, in comparison with terrestrial materials. Over the last decade, Ken Farley has measured helium 3 concentrations in sediments formed over the last 80 million years to create a record of the interplanetary dust flux.

To assure that the peak was not a fluke present at only one site on the seafloor, Farley studied two different localities: one in the Indian Ocean and one in the Atlantic. The event is recorded clearly at both sites.

To find the source of these particles, William F. Bottke and David Nesvorny of the SwRI Space Studies Department in Boulder, Colorado, along with David Vokrouhlicky of Charles University, studied clusters of asteroid orbits that are likely the consequence of ancient asteroidal collisions.

"While asteroids are constantly crashing into one another in the main asteroid belt," says Bottke, "only once in a great while does an extremely large one shatter."

The scientists identified one cluster of asteroid fragments whose size, age, and remarkably similar orbits made it a likely candidate for the Earth-dusting event. Tracking the orbits of the cluster backwards in time using computer models, they found that, 8.2 million years ago, all of its fragments shared the same orbital orientation in space. This event defines when the 100-mile-wide asteroid called Veritas was blown apart by impact and coincides with the spike in the interplanetary seafloor sediments Farley had found.

"The Veritas disruption was extraordinary," says Nesvorny. "It was the largest asteroid collision to take place in the last 100 million years."

As a final check, the SwRI-Czech team used computer simulations to follow the evolution of dust particles produced by the 100-mile-wide Veritas breakup event. Their work shows that the Veritas event could produce the spike in extraterrestrial dust raining on the Earth 8.2 million years ago as well as a gradual decline in the dust flux.

"The match between our model results and the helium 3 deposits is very compelling," Vokrouhlicky says. "It makes us wonder whether other helium 3 peaks in oceanic cores can also be traced back to asteroid breakups."

This research was funded by NASA's Planetary Geology & Geophysics program and received additional financial support from Czech Republic grant agency and the National Science Foundation's COBASE program. The Nature paper is titled "A late Miocene dust shower from the breakup of an asteroid in the main belt."

 

 

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Caltech researchers invent new technique for studying the thermal history of rocks

PASADENA, Calif.—The beautiful valleys of the southern Coast Mountains of British Columbia exist for us to enjoy today because of glacial action in the past. Geologists know, for example, that a giant glacier carved a deep groove in the mountain range to form the present-day Klinaklini Valley. But how fast the cutting actually took place, and when, has hitherto been conjecture.

Now, a 2005 graduate of the California Institute of Technology and his supervising professor have successfully employed a new technique for measuring erosion rates by determining how fast rocks cooled off after being churned up by the glacier. Reporting in the December 9 issue of the journal Science, David Shuster (now at Berkeley Geochronology Center) and Ken Farley, chair of the geological and planetary sciences division at Caltech, along with researchers from Occidental College and the University of Michigan, describe their success in determining how quickly the Klinaklini Valley came into being.

The results show that the two kilometers of overlying rock were removed by the glacier at a rate exceeding five millimeters per year, meaning that the glacial valley deepening occurred six times faster than the normal erosion rate before the glacier came along. The study experimentally confirms the hypothesis that glaciers erode material faster than rivers and are responsible for the topographic relief of mountains. According to Shuster, the study also provides an additional tool for the study of how global climate variations may have influenced mountainous topography.

"This study was possible because of a technique Ken and I developed called helium-helium thermochronometry," Shuster said in a phone interview. "It's an unwieldy name, but it gives us a new way to study the rate at which rocks approached Earth's surface in the past."

The new technique rests on three facts: one, that rocks on the surface have often come from beneath the surface; two, that the ground gets steadily warmer as depth increases; and three, that helium leaks out of a warm rock faster than a cold one. Therefore, if one can figure out how fast the helium leaked out of a rock, then it's also possible to determine how fast the rock cooled and, ultimately, how deeply it was buried, as well as when and how fast it got uncovered.

Helium-helium thermochronometry—or more specifically, 4He/3He thermochronometry—is a novel technique because it requires a rare isotope known as helium-3 to be artificially created in the sample. For this particular study, the researchers collected a calcium phosphate called apatite. As a natural consequence of the decay of uranium and thorium, which exist as trace minerals in apatite, the rock already contains helium-4, but no helium-3.

However, the helium-4 is not dispersed evenly throughout the rock. The dispersal would indeed be even if a rock could just sit for millions of years unheated and unperturbed, but such is not likely in the real world. Rather, the helium-4 tends to leak out during times when the rock is heated. As a consequence, the apatite specimens from the Klinaklini Valley have uneven distributions of helium-4 because the rocks themselves were once beneath the surface. In fact, the ground temperature in the region increases about 25 degrees Celsius for each kilometer of depth.

But while the helium-4 distribution in the apatite samples is a record of how fast the rocks cooled, the researchers cannot determine the rate by looking at helium-4 by itself. For the data necessary to arrive at the rate of cooling, the researchers took the apatite samples to a medical lab in Massachusetts that operates a cyclotron for treating cancer with proton bombardment. By hitting each 100-micron apatite crystal with energetic protons, the researchers managed to create an even dispersal of helium-3 in the samples. The helium-3 comes about as a natural consequence of the proton bombardment.

With both helium-4 and helium-3 now in each apatite sample, the researchers could then compare the ratio of the two isotopes by heating each sample at progressively higher temperatures, making more and more helium leak out, and measuring how much of each isotope was released at each temperature. This allowed them to figure out how the helium-4 was dispersed in each sample and, thus, how fast the rocks had cooled.

"Our technique is for temperatures between about 30 and 70 degrees Celsius," says Farley. "This is the last cooling before a rock comes to the surface, and no other technique accesses this information."

As a result, the team showed that the cooling of the rock happened very quickly about 1.8 million years ago, that the entire valley was carved out in about 300,000 years, and that the total lowering of the area by glacial action was about two kilometers.

"We can say that the glacier was ripping out a huge amount of material and dumping it into the ocean," adds Farley, who is also the Keck Foundation Professor of Geochemistry. "And rather than taking evidence from a single instant, we can for the first time see an integral of hundreds of thousands of years. So this is a new way to get at the rate at which glaciers do their work."

"Why this intense erosion occurred 1.8 million years ago is not well understood, but it seems to coincide with some very interesting changes that took place in Earth's climate system at that time," says Shuster.

According to Shuster, various minerals can be used in the proton-bombardment procedure, although apatite was ideal for the study of the Coast Mountains.

In addition to Shuster and Farley, the other authors are Todd Ehlers, a former postdoctoral researcher at Caltech who is now a member of the University of Michigan faculty, and Margaret Rusmore, a geology professor at Occidental College.

The title of the paper is "Rapid Glacial Erosion at 1.8 Ma Revealed by 4He/3He Thermochronometry."

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Robert Tindol
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Powerful New Supercomputer Analyzes Earthquakes

PASADENA, Calif.- One of the most powerful computer clusters in the academic world has been created at the California Institute of Technology in order to unlock the mysteries of earthquakes.

The Division of Geological and Planetary Sciences' new Geosciences Computational Facility will feature a 2,048-processor supercomputer, housed in the basement of the Seeley G. Mudd Building of Geophysics and Planetary Science on campus.

Computer hardware fills long rows of black racks in the facility, each contains about 35 compute nodes. Massive air conditioning units line an entire wall of the 20-by-80-foot room to re-circulate and chill the air. Miles of optical-fiber cables tie the processors together into a working cluster that went online in September.

The $5.8 million parallel computing project was made possible by gifts from Dell, Myricom, Intel, and the National Science Foundation.

According to Jeroen Tromp, McMillan Professor of Geophysics and director of the Institute's Seismology Lab, who spearheaded the project, "The other crucial ingredient was Caltech's investment in the infrastructure necessary to house the new machine," he says. Some 500 kilowatts of power and 90 tons of air conditioning are needed to operate and cool the hardware.

David Kewley, the project's systems administrator, explained that's enough kilowatts to power 350 average households.

Tromp's research group will share use of the cluster with other division professors and their research groups, while a job-scheduling system will make sure the facility runs at maximum possible capacity. Tromp, who came to Caltech in 2000 from Harvard, is known as one of the world's leading theoretical seismologists. Until now, he and his Institute colleagues have used a smaller version of the machine, popularly known as a Beowulf cluster. Helping revolutionize the field of earthquake study, Tromp has created 3-D simulations of seismic events. He and former Caltech postdoctoral scholar Dimitri Komatitsch designed a computer model that divides the earth into millions of elements. Each element can be divided into slices that represent the earth's geological features.

In simulations involving tens of millions of operations per second, the seismic waves are propagated from one slice to the next, as they speed up, slow down, and change direction according to the earth's characteristics. The model is analogous to a CAT scan of the earth, allowing scientists to track seismic wave paths. "Much like a medical doctor uses a CAT scan to make an image of the brain, seismologists use earthquake-generated waves to image the earth's interior," Tromp says, adding that the earthquake's location, origin time, and characteristics must also be determined.

Tromp will now be able to deliver better, more accurate models in less time. "We hope to use the new machine to do much more detailed mapping. In addition to improving the resolution of our images of the earth's interior, we will also quantitatively assess the devastating effects associated with earthquakes based upon numerical simulations of strong ground motion generated by hypothetical earthquakes."

"One novel way in which we are planning to use the new machine is for near real-time seismology," Tromp adds. "Every time an earthquake over magnitude 3.5 occurs anywhere in California we will routinely simulate the motions associated with the event. Scientific products that result from these simulations are 'synthetic' seismograms that can be compared to actual seismograms."

The "real" seismograms are recorded by the Southern California Seismic Network (SCSN), operated by the Seismo Lab in conjunction with the U.S. Geological Survey. Of interest to the general public, Tromp expects that the collaboration will produce synthetic ShakeMovies of recent quakes, and synthetic ShakeMaps which can be compared to real ShakeMaps derived from the data. "These products should be available within an hour after the earthquake," he says. The Seismology Lab Media Center will be renovated with a large video wall on which scientists can show the results of simulations and analysis.

The new generation of seismic knowledge may also help scientists, engineers, and others lessen the potentially catastrophic effects of earthquakes.

"Intel is proud to be a sponsor of this premier system for seismic research which will be used by researchers and scientists," said Les Karr, Intel Corporate Business Development Manager. "The project reflects Caltech's growing commitment, in both research and teaching, to a broadening range of problems in computational geoscience. It is also a reflection of the growing use of commercial, commodity computing systems to solve some of the world's toughest problems."

The Dell equipment consists of 1,024 dual Dell PowerEdge 1850 servers that were pre-assembled for easy implementation. Dell Services representatives came to campus to complete the installation.

"CITerra, as this new research tool is known on the TOP500 Supercomputer list, is a proud accomplishment both for Caltech and for Myricom," said Charles Seitz, founder and CEO of Myricom, and a former professor of computer science at Caltech. "The talented technical team of Myricom about half of whom are Caltech alumni/ae, are eager for people to know that the architecture, programming methods, and technology of cluster computing was pioneered at Caltech 20 years ago. Those of us at Myricom who have drawn so much inspiration from our Caltech years are delighted to give some of the results of our efforts back to Caltech."

About Myricom: Founded in 1994, Myricom, Inc. created Myrinet, the high-performance computing (HPC) interconnect technology used in thousands of computing clusters in more than 50 countries worldwide. With its next-generation Myri-10G solutions, Myricom is bridging the gap between the rigorous demands of traditional HPC applications and the growing need for affordable computing speed in mainstream enterprises. Privately held, Myricom achieved and has sustained profitability since 1995 with 42 consecutive profitable quarters through September 2005. Based in Arcadia, California, Myricom solutions are sold direct and through channels. Myrinet clusters are supplied by OEM computer companies including IBM, HP, Dell, and Sun, and by other leading cluster integrators worldwide.

About Intel: Intel, the world's largest chipmaker, is also a leading manufacturer of computer, networking, and communications products. Intel processors, platform architectures, interconnects, networking technology, software tools, and services power some of the fastest computers in the world at price points that have expanded high performance computing beyond the confines of elite supercomputer centers and into the broad community of customers in mainstream industries. Those industries span automotive, aerospace, electronics manufacturing, energy and oil and gas in addition to scientific, research and academic organizations.

About the National Science Foundation: The NSF is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..." With an annual budget of about $5.5 billion, it is the funding source for approximately 20 percent of all federally supported basic research conducted by America's colleges and universities. In many fields such as mathematics, computer science, and the social sciences, NSF is the major source of federal backing.

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Contact: Jill Perry (626) 395-3226 jperry@caltech.edu Visit the Caltech Media Relations Web site at: http://pr.caltech.edu/media

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North Atlantic Corals Could Lead to Better Understanding of the Nature of Climate Change

PASADENA, Calif.—The deep-sea corals of the North Atlantic are now recognized as "archives" of Earth's climatic past. Not only are they sensitive to changes in the mineral content of the water during their 100-year lifetimes, but they can also be dated very accurately.

In a new paper appearing in Science Express, the online publication of the American Association for the Advancement of Science (AAAS), environmental scientists describe their recent advances in "reading" the climatic history of the planet by looking at the radiocarbon of deep-sea corals known as Desmophyllum dianthus.

According to lead author Laura Robinson, a postdoctoral scholar at the California Institute of Technology, the work shows in principle that coral analysis could help solve some outstanding puzzles about the climate. In particular, environmental scientists would like to know why Earth's temperature has been holding so steadily for the last 10,000 years or so, after having previously been so variable.

"These corals are a new archive of climate, just like ice cores and tree rings are archives of climate," says Robinson, who works in the Caltech lab of Jess Adkins, assistant professor of geochemistry and global environmental science, and also an author of the paper.

"One of the significant things about this study is the sheer number of corals we now have to work with," says Adkins, "We've now collected 3,700 corals in the North Atlantic, and have been able to study about 150 so far in detail. Of these, about 25 samples were used in the present study.

"To put this in perspective, I wrote my doctoral dissertation with two dozen corals available," Adkins adds.

The corals that are needed to tell Earth's climatic story are typically found at depths of a few hundred to thousands of meters. Scuba divers, by contrast, can go only about 50 to 75 meters below the surface. Besides, the water is bitter cold and the seas are choppy. And to add an additional complication, the corals can be hard to find.

The solution has been for the researchers to take out a submarine to harvest the coral. The star of the ventures so far has been the deep-submergence vehicle known as Alvin, which is famed for having discovered the Titanic some years back. In a 2003 expedition several hundred miles off the coast of New England, Alvin brought back the aforementioned 3,700 corals from the New England Seamounts.

The D. dianthus is especially useful because it lives a long time, can be dated very precisely through uranium dating, and also shows the variations in carbon-14 (or radiocarbon) due to changing ocean currents. The carbon-14 all originally came from the atmosphere and decays at a precisely known rate, whether it is found in the water itself or in the skeleton of a coral. The less carbon-14 found, the "older" the water. This means that the carbon-14 age of the coral would be "older" than the uranium age of the coral. The larger the age difference, the older the water that bathed the coral in the past.

In a perfectly tame and orderly environment, the deepest water would be the most depleted of carbon-14 because the waters at that depth would have allowed the element the most time to decay. A sampling of carbon-14 content at various depths, therefore, would allow a graph to be constructed, in which the maximum carbon-14 content would be found at the surface.

In the real world, however, the oceans circulate. As a result, an "older" mass of water can actually sit on top of a "younger" mass. What's more, the ways the ocean water circulate are tied to climatic variations. A more realistic graph plotting carbon-14 content against depth would thus be rather wavy, with steeper curves meaning a faster rate of new water flushing in, and flatter curves corresponding to relatively unperturbed water.

The researchers can get this information by cutting up the individual corals and measuring their carbon-14 content. During the animals' 100-year life spans, they take in minerals from the water and use the minerals to build their skeletons. The calcium carbonate fossil we see, then, is a skeleton of an animal that may have just died or may have lived thousands of years ago. But in any case, the skeleton is a 100-year record of how much carbon-14 was washing over the creature's body during its lifetime.

An individual coral can tell a story of the water it lived in because the amount of variation in different parts of the growing skeleton is an indication of the kind of water that was present. If a coral sample shows a big increase in carbon-14 about midway through life, then one can assume that a mass of younger water suddenly bathed the coral. On the other hand, if a huge decrease of carbon-14 is observed, then an older water mass must have suddenly moved in.

A coral with no change in the amount of carbon-14 observed in its skeleton means that things were pretty steady during its 100-year lifetime, but the story may be different for a coral at a different depth, or one that lived at a different time.

In sum, the corals tell how the waters were circulating, which in turn is profoundly linked to climatic change, Adkins explains.

"The last 10,000 years have been relatively warm and stable-perhaps because of the overturning of the deep ocean," he says. "The deep ocean has nearly all the carbon, nearly all the heat, and nearly all the mass of the climate system, so how these giant masses of water have sloshed back and forth is thought to be tied to the period of the glacial cycles."

Details of glaciation can be studied in other ways, but getting a history of water currents is a lot more tricky, Adkins adds. But if the ocean currents themselves are implicated in climatic change, then knowing precisely how the rules work would be a great advancement in the knowledge of our planet.

"These guys provide us with a powerful new way of looking into Earth's climate," he says. "They give us a new way to investigate how the rate of ocean overturning has changed in the past."

Robinson says that the current collection of corals all come from the North Atlantic. Future plans call for an expedition to the area southeast of the southern tip of South America to collect corals. The addition of the second collection would give a more comprehensive picture of the global history of ocean overturning, she says.

In addition to Robinson and Adkins, the other authors of the paper are Lloyd Keigwin of the Woods Hole Oceanographic Institute; John Southon of the University of California at Irvine; Diego Fernandez and Shin-Ling Wang of Caltech; and Dan Scheirer of the U.S. Geological Survey office at Menlo Park.

The Science Express article will be published in a future issue of the journal Science.

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Robert Tindol
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Geologists Uncover New Evidence About the Rise of Oxygen

PASADENA, Calif.—Scientists believe that oxygen first showed up in the atmosphere about 2.7 billion years ago. They think it was put there by a one-celled organism called "cyanobacteria," which had recently become the first living thing on Earth to make oxygen from water and sunlight.

The rock record provides a good bit of evidence that this is so. But one of these rocks has just gotten a great deal more slippery, so to speak.

In an article appearing in the Geological Society of America's journal Geology, investigators from the California Institute of Technology, the University of Tübingen in Germany, and the University of Alberta describe their new findings about the origin of the mineral deposits known as banded-iron formations, or "BIFs." A rather attractive mineral that is often cut and polished for paperweights and other decorative items, a BIF typically has alternating bands of iron oxide and silica. How the iron got into the BIFs to begin with is thought to be a key to knowing when molecular oxygen first was produced on Earth.

The researchers show that purple bacteria—primitive organisms that have thrived on Earth without producing oxygen since before cyanobacteria first evolved—could also have laid down the iron oxide deposits that make up BIFs. Further, the research shows that the newer cyanobacteria, which suddenly evolved the ability to make oxygen through photosynthesis, could have even been floating around when the purple bacteria were making the iron oxides in the BIFs.

"The question is what made the BIFs," says Dianne Newman, who is associate professor of geobiology and environmental science and engineering at Caltech and an investigator with the Howard Hughes Medical Institute. "BIFs are thought to record the history of the rise of oxygen on Earth, but this may not be true for all of them."

The classical view of how the BIFs were made is that cyanobacteria began putting oxygen in the atmosphere about 2.7 billion years ago. At the same time, hydrothermal sources beneath the ocean floors caused ferrous iron (that is, "nonrusted" iron) to rise in the water. This iron then reacted with the new oxygen in the atmosphere, which caused the iron to change into ferric iron. In other words, the iron literally "rusted" at the surface of the ocean waters, and then ultimately settled on the ocean floor as sediments of hematite (Fe2O3) and magnetite (Fe3O4).

The problem with this scenario was that scientists in Germany about 10 years ago discovered a way that the more ancient purple bacteria could oxidize iron without oxygen. Instead, these anaerobic bacteria could have used a photosynthetic process in which light and carbon dioxide are used to turn the ferrous iron into ferric iron, throwing the mechanism of BIF formation into question.

Newman's postdoctoral researcher Andreas Kappler (now an assistant professor at the University of Tübingen) expanded on this discovery by doing some lab experiments to measure the rate at which purple bacteria could form ferric iron under light conditions relevant for different depths within the ocean.

Kappler's results showed that iron could indeed have been oxidized by these bacteria, in amounts matching what would have been necessary to form one of the Precambrian iron deposits in Australia.

Another of the paper's Caltech authors, Claudia Pasquero, determined the thickness of the purple bacterial layer that would have been needed for complete iron oxidation. Her results showed that the thickness of the bacterial layer could have been on the order of 17 meters, below wave base, which compares favorably to what is seen today in stratified water bodies such as the Black Sea.

Also, the results show that, in principle, the purple bacteria could have oxidized all the iron seen in the BIFs, even if the cyanobacteria had been present in overlying waters.

However, Newman says that the rock record contains various other kinds of evidence that oxygen was indeed absent in the atmosphere earlier than 2.7 billion years ago. Therefore, the goal of better understanding the history of the rise of oxygen could come down to finding out if there are subtle differences between BIFs that could have been produced by cyanobacteria and/or purple bacteria. And to do this, it's best to look at the biology of the organisms.

"The hope is that we'll be able to find out whether some organic compound is absolutely necessary for anaerobic anoxygenic photosynthesis to occur," Newman says. "If we can know how they work in detail, then maybe we'll be fortunate enough to find one molecule really necessary."

A good candidate is an organic molecule with high geological preservation potential that would have existed in the purple bacteria three billion years ago and still exists today. If the Newman team could find such a molecule that is definitely involved in the changing of iron to iron oxide, and is not present in cyanobacteria, then some of the enigmas of oxygen on the ancient earth would be solved.

"The goals are to get at the types of biomolecules essential for different types of photosynthesis-hopefully, one that is preservable," Newman says.

"I guess one interesting thing from our findings is that you can get rust without oxygen, but this is also about the history of metabolic evolution, and the ability to use ancient rock to investigate the history of life."

Better understanding microbial metabolism could also be of use in NASA's ambitious goal of looking for life on other worlds. The question of which organisms made the BIFs on Earth, therefore, could be useful for astrobiologists who may someday find evidence in rock records elsewhere.

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Robert Tindol
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Cracks or Cryovolcanoes? Surface Geology Creates Clouds on Titan

PASADENA, Calif.-Like the little engine that could, geologic activity on the surface of Saturn's moon Titan-maybe outgassing cracks and perhaps icy cryovolcanoes-is belching puffs of methane gas into the atmosphere of the moon, creating clouds.

This is the conclusion of planetary astronomer Henry G. Roe, a postdoctoral researcher, and Michael E. Brown, professor of planetary astronomy at the California Institute of Technology. Roe, Brown, and their colleagues at Caltech and the Gemini Observatory in Hawaii based their analysis on new images of distinctive clouds that sporadically appear in the middle latitudes of the moon's southern hemisphere. The research will appear in the October 21 issue of the journal Science.

The clouds provide the first explanation for a long-standing Titan mystery: From where does the atmosphere's copious methane gas keep coming? That methane is continuously destroyed by the sun's ultraviolet rays, in a process called photolysis. This photolysis forms the thick blanket of haze enveloping the moon, and should have removed all of Titan's atmospheric methane billions of years ago.

Clearly, something is replenishing the gas-and that something, say Roe and his colleagues, is geologic activity on the surface. "This is the first strong evidence for currently active methane release from the surface," Roe says.

Adds Brown: "For a long time we've wondered why there is methane in the atmosphere of Titan at all, and the answer is that it spews out of the surface. And what is tremendously exciting is that we can see it, from Earth; we see these big clouds coming from above these methane vents, or methane volcanoes. Everyone had thought that must have been the answer, but until now, no one had found the spewing gun."

Roe, Brown, and their colleagues made the discovery using images obtained during the past two years by adaptive optics systems on the 10-meter telescope at the W. M. Keck Observatory on Mauna Kea in Hawaii and the neighboring 8-meter telescope at the Gemini North Observatory. Adaptive optics is a technique that removes the blurring of atmospheric turbulence, creating images as sharp as would be obtained from space-based telescopes.

"These results came about from a collaborative effort between two very large telescopes with adaptive optics capability, Gemini and Keck," says astronomer Chadwick A. Trujillo of the Gemini Observatory, a co-author of the paper. "At both telescopes, the science data were collected from only about a half an hour of images taken over many nights. Only this unusual 'quick look' scheduling could have produced these unique results. At most telescopes, the whole night is given to a single observer, which could not have produced this science."

The two telescopes observed Titan on 82 nights. On 15 nights, the images revealed distinctive bright clouds-two dozen in all-at midlatitudes in the southern hemisphere. The clouds usually popped up quickly, and generally had disappeared by the next day. "We have several observations where on one night, we don't see a cloud, the next night we do, and the following night it is gone," Roe says.

Some of the clouds stretched as much as 2,000 km across the 5,150 km diameter moon. "An equivalent cloud on Earth would cover from the east coast to the west coast of the United States," Roe says. Although the precise altitude of the clouds is not known, they fall somewhere between 10 km and 35 km above the surface, within Titan's troposphere (most cloud activity on the earth is also within its troposphere).

Notably, all of the clouds were located within a relatively narrow band at around 40 degrees south latitude, and most were clustered tightly near 350 degrees west longitude. Both their sporadic appearance and their specific geographic location led the researchers to conclude that the clouds were not arising from the regular convective overturn of the atmosphere due to its heating by the sun (which produces the cloud cover across the moon's southern pole) but, rather, that some process on the surface was creating the clouds.

"If these clouds were due only to the global wind pattern, what we call general circulation, there's no reason the clouds should be linked to a single longitude. They'd be found in a band around the entire moon," Roe says.

Another possible explanation for the clouds' patchy formation is variation in the albedo, or brightness, of the surface. Darker surfaces absorb more sunlight than lighter ones. The air above those warmer spots would be heated, then rise and form convective clouds, much like thunderstorms on a summer's day on Earth. Roe and his colleagues, however, found no differences in the brightness of the surface at 40 degrees south latitude. Clouds can also form over mountains when prevailing winds force air upward, but in that case the clouds should always appear in the identical locations. "We see the clouds regularly appear in the same geographic region, but not always in the exact same location," says Roe.

The other way to make a cloud on Titan is to raise the humidity by directly injecting methane into the atmosphere, and that, the scientists say, is the most likely explanation here.

Exactly how the methane is being injected is still unknown. It may seep out of transient cracks on the surface, or bubble out during the eruption of icy cryovolcanoes.

Although no such features have yet been observed on the moon, Roe and his colleagues believe they may be common. "We think there are numerous sources all over the surface, of varying size, but most below the size that we could see with our instruments," he says.

One large feature near 350 degrees west longitude is probably creating the clump of clouds that forms in that region, while also humidifying the band at 40 degrees latitude, Roe says, "so you end up creating areas where the humidity is elevated by injected methane, making it easier for another, smaller source to also generate clouds. They are like weather fronts that move through. So we are seeing weather, on another planet, with something other than water. With methane. That's cool. It's better than science fiction."

Images are available upon request. For advance copies of the embargoed paper, contact the AAAS Office of Public Programs, (202) 326-6440 or scipak@aaas.org. ###

Contact: Dr. Henry G. Roe (626) 395-8708 hroe@gps.caltech.edu Kathy Svitil Caltech Media Relations (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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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

 

 

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Robert Tindol
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