Geologists Provide New Evidence for Reason Behind Rise of Life in Cambrian Period

PASADENA, Calif.—Geologists have uncovered evidence in the oil fields of Oman that explains how Earth could suddenly have changed 540 million years ago to favor the evolution of the single-celled life forms to the multicellular forms we know today.

Reporting in the December 7 issue of the journal Nature, researchers from MIT, the California Institute of Technology, and Indiana University show that there was a sudden change in the oxygenation of the world's oceans at the time just before the "Cambrian explosion," one of the most significant adaptative radiations in the history of life. With a increased availability of oxygen, the team speculates, single-celled life forms that had dominated the planet for the previous three billion years were able to evolve into the diverse metazoan phyla that still characterize life on Earth.

"The presence of oxygen on Earth is the best indicator of life," says coauthor John Grotzinger, the Fletcher Jones Professor of Geology at Caltech and an authority on sedimentary geology. "But it wasn't always that way. The history of oxygen begins about two and a half billion years ago and occurs in a series of steps. The last step is the subject of this paper."

The key insight was derived when Grotzinger's student Dave Fike, who is lead author of the paper, analyzed core samples and drillings taken at a depth of about three kilometers from oil wells in Oman, which are known to have the oldest commercially viable oil on the planet. The results of carbon and sulfur isotopic analyses from the material led the team to the conclusion that the oceanic conditions that laid down the deposits originally in Oman were quite different from conditions of today.

"You need a very different ocean for these conditions to exist—more like the Black Sea of today, with an upper oxidized layer and lower reduced layer with very little oxygen," says Grotzinger. "The ocean today is pretty well oxidized at all layers, but the ocean before the Cambrian period must have been very different."

When organic matter falls into an ocean that doesn't stir, it becomes deprived of sufficient oxygen and cannot survive as multicellular forms. For this reason, with a limited amount of oxygen, life continued in its single-celled form for the first three billion years.

But about 550 million years ago, according to the team's geologic evidence, the deep ocean began mixing its contents with the shallow ocean, resulting for the first time in a fully oxidized deep ocean.

Characterizing the study as paleoceanography, Grotzinger says the evidence is persuasive because it is so clearly evident in the rock record. Geologists have long believed that the rise of oxygen was a key element involved in the Cambrian radiation, so this discovery really helps solidify that hypothesis.

The oxygen trigger helps account for how life 500 million years ago could have gone from its single-celled existence to the emergence just 10 to 15 million years later of all the metazoan phyla we know today. In short, an abrupt increase in the availability of oxygen may have led to the diversity and complexity of life.

Fike is a graduate student at MIT who is currently in residence at Caltech to work with his professor, Grotzinger, who himself came to Caltech from MIT last year. The other authors of the paper are Lisa Pratt of Indiana University and Roger Summons of MIT.

Writer: 
Robert Tindol
Writer: 

Anticipating Another Sumatran Tsunami

PASADENA, Calif.—Research by the California Institute of Technology, the University of Southern California, and Indonesian scientists indicates that within the next few decades another big tsunami could flood densely populated sections of western coastal Sumatra, south of those that suffered from the tsunami of December 2004.

Four researchers at Caltech and USC have modeled the dynamics of past and plausible future tsunamis.

They hope that such detailed calculations of tsunami characteristics will speed preparations that could save lives. Their work will appear in the Proceedings of the National Academy of Sciences (PNAS) on December 4.

Kerry Sieh, a professor of geology at Caltech and one of the participants in the study, explained, "When we tell people living along this 700-kilometer section of the Sumatran coast that they will likely experience a big tsunami within the next 30 years, they ask for details. How much time after the earthquake will they have before the tsunami strikes? How big will the waves be? How far inland should they be prepared to run? What areas are likely to suffer tsunami damage? This paper is our first attempt to answer these important questions."

The same big fault, or megathrust, that caused the tsunami of 2004 extends much farther southeastward, beneath the Indian Ocean, just off the southwest coast of Sumatra. Rupture of this section of the megathrust, under the Mentawai Islands, produced two great quakes and tsunamis in 1797 and 1833. Such events appear to recur on average every 230 years.

Samples of coral from the islands show how much these previous quakes lifted the seafloor. The patterns of uplift gave the scientists the information they needed to do computer simulations of the historical tsunamis. Costas Synolakis, director of the USC Viterbi School of Engineering's Tsunami Research Center, says that the impact of the computed 1797 and 1833 tsunamis is consistent with historical accounts.

This consistency increased the scientists' confidence in using the same model to evaluate worst-case scenarios for future tsunamis, which, according to Jose Borrero, lead author of the study, "confirm a substantial exposure of coastal Sumatran communities to tsunami surges." For example, two river valleys near Bengkulu, a coastal city of about 350,000 people, experience flooding that extends up to several kilometers inland.

In the models of future tsunamis, offshore islands appear to shield the larger city of Padang somewhat, but even there the 1797 tsunami reportedly carried a 200-ton English ship into the town, approximately a kilometer upstream, and smaller vessels were carried yet further.

"The population of Padang in 1797 and 1833 was a few thousand," Sieh says. "Now it is about 800,000, and most of it is within a few meters of sea level. We hope that these initial results will help focus educational efforts, emergency preparedness activities, and changes in the basic infrastructure of cities and towns along the Sumatran coast," Adds Synolakis, "The message of the 2004 tsunami has not been lost in the research community. We are trying to be proactive and help prevent a disaster like Aceh in 2004."

This tsunami study is the work of four Southern California researchers. Jose Borrero is a scientist at USC's Tsunami Research Center. Kerry Sieh is the Robert P. Sharp professor of geology at Caltech. Mohamed Chlieh is a postdoctoral scholar at Caltech's Tectonics Observatory. Costas Synolakis is a professor in the department of civil and environmental engineering in the USC Viterbi School of Engineering and director of its Tsunami Research Center.

Writer: 
John Avery
Writer: 

Geobiologists Solve "Catch-22 Problem" Concerning the Rise of Atmospheric Oxygen

PASADENA, Calif.—Two and a half billion years ago, when our evolutionary ancestors were little more than a twinkle in a bacterium's plasma membrane, the process known as photosynthesis suddenly gained the ability to release molecular oxygen into Earth's atmosphere, causing one of the largest environmental changes in the history of our planet. The organisms assumed responsible were the cyanobacteria, which are known to have evolved the ability to turn water, carbon dioxide, and sunlight into oxygen and sugar, and are still around today as the blue-green algae and the chloroplasts in all green plants.

But researchers have long been puzzled as to how the cyanobacteria could make all that oxygen without poisoning themselves. To avoid their DNA getting wrecked by a hydroxyl radical that naturally occurs in the production of oxygen, the cyanobacteria would have had to evolve protective enzymes. But how could natural selection have led the cyanobacteria to evolve these enzymes if the need for them didn't even exist yet?

Now, two groups of researchers at the California Institute of Technology offer an explanation of how cyanobacteria could have avoided this seemingly hopeless contradiction. Reporting in the December 12 Proceedings of the National Academy of Sciences (PNAS) and available online this week, the groups demonstrate that ultraviolet light striking the surface of glacial ice can lead to the accumulation of frozen oxidants and the eventual release of molecular oxygen into the oceans and atmosphere. This trickle of poison could then drive the evolution of oxygen-protecting enzymes in a variety of microbes, including the cyanobacteria. According to Yuk Yung, a professor of planetary science, and Joe Kirschvink, the Van Wingen Professor of Geobiology, the UV-peroxide solution is "rather simple and elegant."

"Before oxygen appeared in the atmosphere, there was no ozone screen to block ultraviolet light from hitting the surface," Kirschvink explains. "When UV light hits water vapor, it converts some of this into hydrogen peroxide, like the stuff you buy at the supermarket for bleaching hair, plus a bit of hydrogen gas.

"Normally this peroxide would not last very long due to back-reactions, but during a glaciation, the hydrogen peroxide freezes out at one degree below the freezing point of water. If UV light were to have penetrated down to the surface of a glacier, small amounts of peroxide would have been trapped in the glacial ice." This process actually happens today in Antarctica when the ozone hole forms, allowing strong UV light to hit the ice.

Before there was any oxygen in Earth's atmosphere or any UV screen, the glacial ice would have flowed downhill to the ocean, melted, and released trace amounts of peroxide directly into the sea water, where another type of chemical reaction converted the peroxide back into water and oxygen. This happened far away from the UV light that would kill organisms, but the oxygen was at such low levels that the cyanobacteria would have avoided oxygen poisoning.

"The ocean was a beautiful place for oxygen-protecting enzymes to evolve," Kirschvink says. "And once those protective enzymes were in place, it paved the way for both oxygenic photosynthesis to evolve, and for aerobic respiration so that cells could actually breathe oxygen like we do."

The evidence for the theory comes from the calculations of lead author Danie Liang, a recent graduate in planetary science at Caltech who is now at the Research Center for Environmental Changes at the Academia Sinica in Taipei, Taiwan.

According to Liang, a serious freeze-over known as the Makganyene Snowball Earth occurred 2.3 billion years ago, at roughly the time cyanobacteria evolved their oxygen-producing capabilities. During the Snowball Earth episode, enough peroxide could have been stored to produce nearly as much oxygen as is in the atmosphere now.

As an additional piece of evidence, this estimated oxygen level is also sufficient to explain the deposition of the Kalahari manganese field in South Africa, which has 80 percent of the economic reserves of manganese in the entire world. This deposit lies immediately on top of the last geological trace of the Makganyene Snowball.

"We used to think it was a cyanobacterial bloom after this glaciation that dumped the manganese out of the seawater," says Liang. "But it may have simply been the oxygen from peroxide decomposition after the Snowball that did it."

In addition to Kirschvink, Yung, and Liang, the other authors are Hyman Hartman of the Center for Biomedical Engineering at MIT, and Robert Kopp, a graduate student in geobiology at Caltech. Hartman, along with Chris McKay of the NASA Ames Research Center, were early advocates for the role that hydrogen peroxide played in the origin and evolution of oxygenic photosynthesis, but they could not identify a good inorganic source for it in Earth's precambrian environment.

The paper is available online at the following Web address: http://www.pnas.org/papbyrecent.shtml

Writer: 
Robert Tindol
Writer: 

Watson Lecture: Natural Disasters

PASADENA, Calif.- The recent devastations caused by earthquakes in south and southwest Asia, by the Indian Ocean tsunami, and by hurricane Katrina offer dramatic proof that communities all over the world are both unaware of, and unprepared for, natural hazards. Unfortunately, while scientists understand much about these natural hazards, that knowledge commonly is not used to reduce the risks.

"Even though we scientists and engineers often can characterize what will happen, there is a big gap between what we know about nature and how people respond to what we know," says Kerry Sieh, the Robert P. Sharp Professor of Geology at the California Institute of Technology. "Thus, with the enormous growth of the human population over the past half-century, it seems inescapable that natural events will take an ever-increasing toll in lives, well-being and property."

On Wednesday, October 18, Sieh will take a look at a few particular natural disasters and what is being done to mitigate their effects. His talk, "Natural Disasters: What We Know vs. What We Do," is the first program of the 2006-2007 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 2006-2007 series include

o Christopher E. Brennen, Richard L. and Dorothy M. Hayman Professor of Mechanical Engineering, Caltech, on "The Amazing World of Bubbles," November 8.

o Philip T. Hoffman, Richard and Barbara Rosenberg Professor of History and Social Science, Caltech, on "Why Did Europe Conquer the World? How Politics and Economics Created a Comparative Advantage in Violence," December 6.

o Melany L. Hunt, professor of mechanical engineering and executive officer for mechanical engineering, Caltech, on "Booming Sand Dunes," January 17, 2007.

For more information, call (626) 395-4652. Outside the greater Pasadena area, call toll-free, 1(888) 2CALTECH (1-888-222-5832).

###

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

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

Writer: 
JA
Writer: 

The Dwarf Planet Formerly Known as Xena Has Officially Been Named Eris, IAU Announces

PASADENA, Calif.—The International Astronomical Union (IAU) today announced that the dwarf planet known as Xena since its 2005 discovery has been named Eris, after the Greek goddess of discord.

Eris's moon will be known as Dysnomia, the demon goddess of lawlessness and the daughter of Eris.

The names are those suggested by the discoverers of the dwarf planet—Mike Brown, a professor of planetary astronomy at the California Institute of Technology, Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale University, and by the discoverers of the moon—Brown and the engineering team of Keck Observatory where the observations were made.

"Eris is the Greek goddess of discord and strife," explains Brown. "She stirs up jealousy and envy to cause fighting and anger among men. At the wedding of Peleus and Thetis, all the gods were invited with the exception of Eris, and, enraged at her exclusion, she spitefully caused a quarrel among the goddesses that led to the Trojan War.

"She's quite a fun goddess, really," Brown adds. "And, for the Xena fans out there who are sad to see the name go, Eris appeared in her Latin version of Discordia as a recurring character on Xena: Warrior Princess."

True to its name, the dwarf planet Eris has stirred up a great deal of trouble among the international astronomical community, most recently last month when the question of its proper designation led to a raucous meeting of the IAU in Prague. At the end of the conference, IAU members voted to demote Pluto to dwarf-planet status, leaving the solar system with eight planets.

However, the ruling effectively settled the year-long controversy about whether Eris would rise to planetary status. Somewhat larger than Pluto, the body was formally announced to the world on July 29, 2005. With the August IAU ruling, Eris is the largest dwarf planet.

Eris, about 2,400 kilometers in diameter, was discovered on January 8, 2005, at Palomar Observatory with the NASA-funded 48-inch Samuel Oschin Telescope. A Kuiper-belt object like Pluto, but slightly less reddish-yellow, Eris is currently visible in the constellation Cetus to anyone with a top-quality amateur telescope.

Eris is now about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), which means that it is some nine billion miles away at present. On a highly elliptical 560-year orbit, Eris sweeps in as close to the sun as 38 astronomical units. At present, however, it is nearly as far away as it ever gets.

Pluto's own elliptical orbit takes it as far away as 50 astronomical units from the sun during its 250-year revolution. This means that Eris is sometimes much closer to Earth than Pluto—although never closer than Neptune.

Dysnomia, the only satellite of Eris discovered so far, is about 250 kilometers in diameter and reflects only about 1 percent of the sunlight that its parent reflects. The name is both a nod to Lucy Lawless, the actress who played Xena on the TV show, and to the astronomical tradition of naming the first satellites of dwarf planets.

Based on spectral data, the researchers think Eris is covered with a layer of methane that has seeped from the interior and frozen on the surface. As in the case of Pluto, the methane has undergone chemical transformations, probably due to the faint solar radiation, causing the methane layer to redden. But the methane surface on Eris is somewhat more yellowish than the reddish-yellow surface of Pluto, perhaps because Eris is farther from the sun.

Brown, Trujillo, and Rabinowitz first photographed Eris with the Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of 2005.

The search for new planets and other bodies in the Kuiper belt is funded by Caltech and NASA. For more information on the program, see the Samuel Oschin Telescope's website at http://www.astro.caltech.edu/palomarnew/sot.html.

For more information on Mike Brown's research, see http://www.gps.caltech.edu/~mbrown.

To learn more about Eris, see http://www.planeteris.com.

 

Writer: 
Robert Tindol
Writer: 

Xena Awarded "Dwarf Planet" Status, IAU Rules; Solar System Now Has Eight Planets

PASADENA, Calif.—The International Astronomical Union (IAU) today downgraded the status of Pluto to that of a "dwarf planet," a designation that will also be applied to the spherical body discovered last year by California Institute of Technology planetary scientist Mike Brown and his colleagues. The decision means that only the rocky worlds of the inner solar system and the gas giants of the outer system will hereafter be designated as planets.

The ruling effectively settles a year-long controversy about whether the spherical body announced last year and informally named "Xena" would rise to planetary status. Somewhat larger than Pluto, the body has been informally known as Xena since the formal announcement of its discovery on July 29, 2005, by Brown and his co-discoverers, Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University. Xena will now be known as the largest dwarf planet.

"I'm of course disappointed that Xena will not be the tenth planet, but I definitely support the IAU in this difficult and courageous decision," said Brown. "It is scientifically the right thing to do, and is a great step forward in astronomy.

"Pluto would never be considered a planet if it were discovered today, and I think the fact that we've now found one Kuiper-belt object bigger than Pluto underscores its shaky status."

Pluto was discovered in 1930. Because of its size and distance from Earth, astronomers had no idea of its composition or other characteristics at the time. But having no reason to think that many other similar bodies would eventually be found in the outer reaches of the solar system—or that a new type of body even existed in the region—they assumed that designating the new discover as the ninth planet was a scientifically accurate decision.

However, about two decades later, the famed astronomer Gerard Kuiper postulated that a region in the outer solar system could house a gigantic number of comet-like objects too faint to be seen with the telescopes of the day. The Kuiper belt, as it came to be called, was demonstrated to exist in the 1990s, and astronomers have been finding objects of varying size in the region ever since.

Few if any astronomers had previously called for the Kuiper-belt objects to be called planets, because most were significantly smaller than Pluto. But the announcement of Xena's discovery raised a new need for a more precise definition of which objects are planets and which are not.

According to Brown, the decision will pose a difficulty for a public that has been accustomed to thinking for the last 75 years that the solar system has nine planets.

"It's going to be a difficult thing to accept at first, but we will accept it eventually, and that's the right scientific and cultural thing to do," Brown says.

In fact, the public has had some experience with the demotion of a planet in the past, although not in living memory. Astronomers discovered the asteroid Ceres on January 1, 1801—literally at the turn of the 19th century. Having no reason to suspect that a new class of celestial object had been found, scientists designated it the eighth planet (Uranus having been discovered some 20 years earlier).

Soon several other asteroids were discovered, and these, too, were summarily designated as newly found planets. But when astronomers continued finding numerous other asteroids in the region (there are thought to be hundreds of thousands), the astronomical community in the early 1850s demoted Ceres and the others and coined the new term "minor planet."

Xena was discovered on January 8, 2005, at Palomar Observatory with the NASA-funded 48-inch Samuel Oschin Telescope. Xena is about 2,400 kilometers in diameter. A Kuiper-belt object like Pluto, but slightly less reddish-yellow, Xena is currently visible in the constellation Cetus to anyone with a top-quality amateur telescope.

Brown and his colleagues in late September announced that Xena has at least one moon. This body has been nicknamed Gabrielle, after Xena's sidekick on the television series.

Xena is currently about 97 astronomical units from the sun (an astronomical unit is the distance between the sun and Earth), which means that it is some nine billion miles away at present. Xena is on a highly elliptical 560-year orbit, sweeping in as close to the sun as 38 astronomical units. Currently, however, it is nearly as far away as it ever gets.

Pluto's own elliptical orbit takes it as far away as 50 astronomical units from the sun during its 250-year revolution. This means that Xena is sometimes much closer to Earth than Pluto—although never closer than Neptune.

Gabrielle is about 250 kilometers in diameter and reflects only about 1 percent of the sunlight that its parent reflects. Because of its small size, Gabrielle could be oddly shaped.

Brown says that the study of Gabrielle's orbit around Xena hasn't yet been fully completed. But once it is, the researchers will be able to derive the mass of Xena itself from Gabrielle's orbit. This information will lead to new insights on Xena's composition.

Based on spectral data, the researchers think Xena is covered with a layer of methane that has seeped from the interior and frozen on the surface. As in the case of Pluto, the methane has undergone chemical transformations, probably due to the faint solar radiation, that have caused the methane layer to redden. But the methane surface on Xena is somewhat more yellowish than the reddish-yellow surface of Pluto, perhaps because Xena is farther from the sun.

Brown and Trujillo first photographed Xena with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of 2005.

The search for new planets and other bodies in the Kuiper belt is funded by NASA. For more information on the program, see the Samuel Oschin Telescope's website at http://www.astro.caltech.edu/palomarnew/sot.html.

For more information on Mike Brown's research, see http://www.gps.caltech.edu/~mbrown.

Writer: 
Robert Tindol
Writer: 

Study of 8.7-Magnitude Earthquake Lends New Insight into Post-Shaking Processes

PASADENA, Calif.—Although the magnitude 8.7 Nias-Simeulue earthquake of March 28, 2005, was technically an aftershock, the temblor nevertheless killed more than 2,000 people in an area that had been devastated just three months earlier by the December 2004, magnitude 9.1 earthquake. Now, data returned from instruments in the field provide constraints on the behavior of dangerous faults in subduction zones, fueling a new understanding of basic mechanics controlling slip on faults, and in turn, improved estimates of regional seismic risk.

In the June 30 issue of the journal Science, a team including Ya-Ju Hsu, Mark Simons, and others of the California Institute of Technology's new Tectonics Observatory and the University of California, San Diego, report that their analysis of Global Positioning System (GPS) data taken at the time of the earthquake and during the following 11 months provide insights into how fault slippage and aftershock production are related.

"In general, the largest earthquakes occur in subduction zones, such as those offshore of Indonesia, Japan, Alaska, Cascadia, and South America," says Hsu, a postdoctoral researcher at the Tectonics Observatory and lead author of the paper. "Of course, these earthquakes can be extremely damaging either directly, or by the resulting tsunami.

"Therefore, understanding what causes the rate of production of aftershocks is clearly important to earthquake physics and disaster response," Hsu adds.

The study finds that the regions on the fault surrounding the area that slipped during the 8.7 earthquake experienced accelerated rates of slip following the March shock. The region dividing the area that slipped during the earthquake, and that which has slipped after the earthquake, is clearly demarcated by a band of intense aftershocks.

A primary conclusion of the paper is that there is a strong relationship between the production of aftershocks and post-earthquake fault slip-in other words, the frequency and location of aftershocks in a subduction megathrust are related to the amount and location of fault slip in the months following the main earthquake. Hsu and her colleagues believe that the aftershocks are controlled by the rate of aseismic fault slip after the earthquake.

"One conjecture is that, if the aseismic fault slip occurs quickly, then lots of aftershocks are produced," says Simons, an associate professor of geophysics at Caltech. "But there are other arguments suggesting that both the aftershocks and the post-earthquake aseismic fault slip are caused by some third underlying process."

In any case, Simons and Hsu say that the study demonstrates that the placing of additional remote sensors in subduction zones leads to better modeling of earthquake hazards. In particular, the study shows that the rheology, or mechanical properties, of the region can be inferred from the accumulation of postseismic data.

A map of the region constructed from the GPS data reveals that certain areas slip in different manners than others because some parts of the fault seem to be more "sticky." Because of the nature of seismic waves, the manner in which the fault slips in the months following a large earthquake has huge implications for human habitation.

"An important question is how slip on a fault varies as a function of time," Simons explains. "The extent to which an area slips is related to the risk, because you have a finite budget. Whether all the stress is released during earthquakes or whether it creeps is important for us to know. We would be very happy if all faults slipped as a slow creep, although I guess seismologists would be out of work."

The fact that the Nias-Simeulue's postseismic slip following the December 28, 2004, earthquake can be modeled so intricately shows that other subduction zones can also be modeled, Hsu says. "In general, understanding the whole seismic cycle is very important. Most of the expected hazards of earthquakes occur in subduction zones."

The Tectonics Observatory is establishing a network of sensors in areas of active plate-boundary deformation such as Chile and Peru, the Kuril Islands off Japan, and Nepal. The observatory is supported by the Gordon and Betty Moore Foundation.

The other authors of the paper are Jean-Philippe Avouac, a professor of geology at Caltech and director of the Tectonics Observatory; Kerry Sieh, the Sharp Professor of Geology at Caltech; John Galetzka, a professional staff member at Caltech; Mohamed Chlieh, a postdoctoral scholar at Caltech; Danny Natawidjaja of the Indonesian Institute of Sciences; and Linette Prawfrodirdjo and Yehuda Bock, both of the University of California at San Diego's Institute of Geophysics and Planetary Sciences.

Writer: 
Robert Tindol
Writer: 

Hubble Space Telescope Obtains Best-Ever Size Measurement of Xena; Still Larger Than Pluto

PASADENA, Calif.—To paraphrase a certain young lady from literature, the tenth planet Xena is getting curiouser and curiouser. Data released today by the Space Telescope Science Institute reveals that Xena is about 5 percent larger than Pluto, which means that it must be the most reflective planet in the solar system.

According to Mike Brown, a California Institute of Technology planetary scientist who codiscovered Xena last year, the Hubble Space Telescope measurement shows that Xena is about 2,400 kilometers in diameter, give or take 100 kilometers. The planet's smaller-than-expected size, together with its distance from Earth and its brightness, mean that Xena must reflect 86 percent of all light.

"This makes it more reflective than the nine known planets, and more reflective than everything else other than Enceladus," explains Brown. Enceladus is a moon orbiting Saturn.

Brown and his colleagues, Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University, publicly announced the discovery of Xena on July 29, 2005. Their argument from the beginning has been that Xena deserves to be formally declared the tenth planet because it is larger than Pluto. If the designation is approved by the International Astronomical Union, Xena will assume a formal new name that will presumably be taken from Greek or Roman mythology, and will become only the fourth planet to have been discovered in historical times.

Also designated as 2003 UB313, Xena was originally found by Brown, Trujillo, and Rabinowitz with the NASA-funded 48-inch Samuel Oschin Telescope at Caltech's Palomar Observatory. Like its nine siblings, Xena independently orbits the sun, and like Pluto, is a Kuiper-belt object.

Brown says the high reflectivity of Xena is surprising, but perhaps explainable. "I think what is going on, is that the temperature of Xena-which is about minus 400 degrees Fahrenheit-causes the atmosphere to be frozen to the surface. This frozen atmosphere would make a nice, bright layer a few inches thick.

"When Xena gets closer to the sun and heats up to a sultry 370 degrees below zero, the frozen atmosphere probably re-evaporates and the surface probably looks more like Pluto for a time. But Xena is currently 10 billion miles from the sun, and because of its distance is about as cold as it ever gets."

The situation will change, however, when Xena approaches closer to the sun on its 560-year elliptical orbit. Though we won't live to see it, Xena will eventually get within 38 astronomical units of Earth (in other words, 38 times the distance between the sun and Earth), and things will heat up significantly.

"Xena is about to undergo the worst case of global warming of any planet in the solar system," says Brown. "The change will be equivalent to Earth's heating up to an average temperature of 400 degrees! But then the cycle will repeat and Xena will get cold again."

Xena's closest planetary neighbor is Pluto, which Xena resembles in various ways. Pluto's own elliptical orbit takes it as far away as 50 astronomical units from the sun during its 250-year trip around the sun. This means that Xena is sometimes much closer to Earth than Pluto-although never closer than Neptune.

Since the discovery, Brown and his colleagues have intensely studied the planet with a variety of instruments, and have already learned many of its characteristics. In the course of their investigations, they have also discovered that the new planet has a small moon. This body, unofficially nicknamed "Gabrielle" after Xena's sidekick on the television show, will also be formally named at a later date. Gabrielle is about 250 kilometers in diameter and reflects only about 1 percent of the sunlight that its parent reflects. Because of its small size, Gabrielle may very well be oddly shaped.

Brown says that Gabrielle's orbit around Xena hasn't yet been fully determined. But once it is, the researchers will be able to derive the mass of the planet itself. That's because the entire mass of the system (planet and moon together) orbits a common center of gravity. Therefore, once the researchers figure out the distance between moon and planet, how fast the moon revolves around the planet, and how much the moon makes the planet wobble, then they'll know how much Xena weighs. And this information will lead to new insights on its composition.

Based on spectral data, the researchers think the planet is covered with a layer of methane that has seeped from the interior. As in the case of Pluto, the methane has undergone chemical transformations, probably due to the faint solar radiation that has caused the methane layer to redden. But the methane surface on Xena is somewhat more yellowish than the reddish-yellow surface of Pluto, perhaps because Xena is farther from the sun.

Brown and Trujillo first photographed the new planet with the 48-inch Samuel Oschin Telescope on October 31, 2003. However, the object was so far away that its motion was not detected until they reanalyzed the data in January of last year.

The search for new planets and other bodies in the Kuiper belt is funded by NASA. For more information on the program, see the Samuel Oschin Telescope's Website at http://www.astro.caltech.edu/palomarnew/sot.html

For more information on Mike Brown's research, see http://www.gps.caltech.edu/~mbrown.

Writer: 
Robert Tindol
Writer: 

Watson Lecture: Bacterial Biofilms

PASADENA, Calif.- Next time you're brushing your teeth in the morning, give a thought to biofilms, the complex communities of bacteria that form the slippery scum you're scouring off your teeth, along with the slime on river rocks, the gunk in clogged drains, and filmy coatings on just about any surface, anywhere, that's exposed to water.

Biofilms--and the bacteria that comprise them--"get a bad rap," says Dianne K. Newman, "but pathogenic bacteria are only a very minor fraction of those in nature. The vast majority of bacteria do really wonderful and important things."

On Wednesday, April 12, Newman, professor of geobiology at the California Institute of Technology and investigator at the Howard Hughes Medical Institute, will discuss how biofilms and bacteria in general are essential for our health and how they have sustained and shaped our environment throughout Earth's history. "I hope that people come to appreciate that bacteria are more than just germs and are, in fact, remarkably metabolically sophisticated," she says. Her talk, "Bacterial Biofilms: Far More Than a Collection of Germs," is the second program of the Winter/Spring 2006 Earnest C. Watson Lecture Series.

The lecture 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.

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

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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Fault That Produced Largest Aftershock Ever Recorded Still Poses Threat to Sumatra

PASADENA, Calif.—A mere three months after the giant Sumatra-Andaman earthquake and tsunami of December 2004, tragedy struck again when another great earthquake shook the area just to the south, killing over 2,000 Indonesians. Although technically an aftershock of the 2004 event, the 8.7-magnitude Nias-Simeulue earthquake just over a year ago was itself one of the most powerful earthquakes ever recorded. Only six others have had greater magnitudes.

In the March 31 issue of the journal Science, a team of researchers led by Richard Briggs and Kerry Sieh of the California Institute of Technology reconstruct the fault rupture that caused the March 28, 2005, event from detailed measurements of ground displacements. Their analysis shows that the fault broke along a 400-kilometer length, and that the length of the break was limited by unstrained sections of the fault on either end.

The researchers continue to express concern that another section of the great fault, south of the 2005 rupture, is likely to cause a third great earthquake in the not-too-distant future. The surface deformation they observed in the 2005 rupture area may well be similar to what will occur when the section to the south ruptures.

Briggs, a postdoctoral scholar in Caltech's new Tectonics Observatory, and his colleagues determined the vertical displacements of the Sumatran islands that are directly over the deeply buried fault whose rupture generated the 2005 earthquake. The main technique they used was the examination of coral heads growing near the shore. The tops of these heads stay just at the waterline, so if they move higher or lower, it indicates that there has been uplift or subsidence.

The researchers also obtained data on ground displacements from GPS stations that they had rushed into place after the 2004 earthquake. "We were fortunate to have installed the geodetic instruments right above the part that broke," says Kerry Sieh, who leads the Sumatran project of Caltech's Tectonics Observatory. "This is the closest we've ever gotten to such a large earthquake with continuously recording GPS instruments."

From the coral and GPS measurements, the researchers found that the 2005 earthquake was associated with uplift of up to three meters over a 400-kilometer stretch of the Sunda megathrust, the giant fault where Southeast Asia is overriding the Indian and Australian plates. This stretch lies to the south of the 1600-kilometer section of the fault that ruptured in 2004.

Actual slippage on the megathrust surface (about 25 kilometers below the islands) was over 11 meters. The data permitted calculation of the earthquake's magnitude at 8.6, nearly the same as estimates based on seismological recordings.

Most of the deaths in the 2005 earthquake were the direct result of shaking and the collapse of buildings. The earthquake did not trigger a disastrous tsunami comparable to the one that followed the 2004 event. In part, this was because the 2005 rupture was smaller-about one-quarter the length and one-half the slip.

In addition, the largest uplift lay under offshore islands, where there was no water to be displaced. Finally, by rising during the earthquake, the islands gained some instant, extra protection for when the tsunami reached them tens of minutes later.

The scientists were surprised to find that the southern end of the 2004 rupture and the northern end of the 2005 rupture did not quite abut each other, but were separated by a short segment under the island of Simeulue on which the amount of slip was nearly zero. They infer that this segment had not accumulated enough strain to rupture during either event-perhaps, they speculate, because it slips frequently and therefore relieves strain without generating large earthquakes.

Thus, this segment might act as a barrier to rupture propagation. A similar 170-kilometer "creeping" section of the San Andreas fault, between San Francisco and Los Angeles, separates the long section that produced Northern California's great 1906 earthquake from the long section that ruptured during Southern California's great 1857 earthquake.

The southern end of the 2005 rupture was at another short "creeping" segment or weak patch. "Both ends of the 2005 rupture seem to have been at the edges of a weak patch," Sieh explains. The 2005 event therefore probably represents a "characteristic earthquake" that has recurred often over geological time. In fact, old historical records suggest that a very similar earthquake was caused by a rupture of this segment in 1861.

Sieh suggests that installation of GPS instruments along the world's other subduction megathrusts could help more clearly to define those sections that creep stably versus the segments that are locked and thus more likely to break in infrequent, but potentially devastating, ruptures.

Previous work by the Caltech group and their Indonesian colleagues has shown that south of the southern creeping segment lies another locked segment, about 600 kilometers long, which has not broken since a magnitude 9.0 earthquake in 1833. Corals and coastlines along the southern segment record decades of continual, pronounced subsidence, similar to the behavior of the northern region prior to its abrupt uplift during the 2005 fault rupture.

"This southern part is very likely about ready to go again," Sieh says. "It could devastate the coastal communities of southwestern Sumatra, including the cities of Padang and Bengkulu, with a combined population of well over a million people. It could happen tomorrow, or it could happen 30 years from now, but I'd be surprised if it were delayed much beyond that."

Sieh and his colleagues are engaged in efforts to increase public awareness and preparedness for future great earthquakes and tsunamis in Sumatra.

The Science paper is titled "Deformation and slip along the Sunda megathrust in the great 2005 Nias-Simeulue earthquake." The other authors are Aron Meltzner, John Galetzka, Ya-ju Hsu, Mark Simons, and Jean-Philippe Avouac, all at Caltech's Tectonics Observatory; Danny Natawidjaja, Bambang Suwargadi, Nugroho Hananto, and Dudi Prayudi, all at the Indonesian Institute of Sciences; Imam Suprihanto of Jakarta; and Linette Prawirodirdjo and Yehuda Bock at the Scripps Institution of Oceanography.

The research was funded by the Gordon and Betty Moore Foundation, the National Science Foundation, and NASA.

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