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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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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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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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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Evolutionary Accident Probably Caused The Worst Snowball Earth Episode, Study Shows

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Kirschvink is Caltech's Van Wingen Professor of Geobiology.

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

 

 

 

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Robert Tindol
Writer: 

Planetary Scientists Discover Tenth Planet

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

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

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

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

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

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

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

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

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

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

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RT

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

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

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

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

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

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

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

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

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

 

 

Writer: 
Robert Tindol
Writer: 

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

Writer: 
Robert Tindol
Writer: 

First Planet Under Three Suns Is Discovered

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

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

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

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

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

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

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

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

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

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

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

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

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

The research was funded by NASA.

 

 

Writer: 
Robert Tindol
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