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."




Robert Tindol

Caltech Scientists Create Tiny Photon Clock

PASADENA--In a new development that could be useful for future electronic devices, applied physicists at the California Institute of Technology have created a tiny disk that vibrates steadily like a tuning fork while it is pumped with light. This is the first micro-mechanical device that has been operated at a steady frequency by the action of photons alone.

Reporting in recently published issues of the journals Optics Express (July 11) and Physical Review Letters (June 10 and July 11), Kerry Vahala and group members Hossein Rokhsari, Tal Carmon, and Tobias Kippenberg, explain how the tiny, disk-shaped resonator made of silica can be made to vibrate mechanically when hit by laser light. The disk, which is less than the width of a human hair, vibrates about 80 million times per second when its rim is pumped with light.

According to Vahala, who is the Jenkins Professor of Information Science and Technology and Professor of Applied Physics, the effect is due to properties of the disk that allow it to store light very efficiently, and also to the fact that light exerts "radiation pressure." In much the same way that NASA's solar sails will catch photons from the sun to power spaceships to other worlds, the disk builds up light energy so that the disk itself swells.

"The light makes hundreds of thousands of orbits around the rim of the disk," Vahala explains. "This causes the disk to literally stretch, owing to the radiation pressure of the photons."

Once the disk has inflated, its physical properties change so that the light energy is lost, and the disk then deflates. The cycle then repeats itself, and this repetition continues in a very orderly fashion as long as the light is pumped into the disk.

In effect, this repetitive process makes the disk a very efficient clock, somewhat similar to the quartz crystal that is made to vibrate from electrical current for the regulation of a battery-powered wristwatch. The differences between the optically driven clock and the traditional electrical one, however, create a design element that could provide new electro-optic functions within the context of integrated circuits.

The researchers also note that whereas the basic operation of the device can be understood at the classical level, such a device could be used to study interactions between radiation and macroscopic mechanical motion at the quantum level. Several groups have already proposed theoretically using radiation pressure as a mechanism to investigate such interactions.

Also, the device could be of help in designing the next-generation Laser Interferometer Gravitational-Wave Observatory (LIGO). A National Science Foundation-funded project operated by Caltech and MIT, LIGO and has been created to detect the phenomenon known as gravitational waves, predicted by Einstein decades ago.

LIGO is designed in such a way that laser light bounces between mirrors along a five-mile right-angle circuit. The light is allowed to build up in the two arms of the detector so as to increase the possibility that gravitational waves will eventually be detected from exotic astrophysical objects such as colliding black holes and supernovae.

But designers have been concerned to ensure that the same radiation-pressure-driven instability does not appear in the LIGO system as its sensitivity is boosted. The work by the Vahala group, though at a vastly smaller size scale, therefore could be of help in the current plans for improvement of the LIGO detectors in Hanford, Washington and Livingston, Louisiana.

"This work demonstrates a mechanism that needs to be understood better," Vahala explains. "It has moved from theory to existence, and that is always exciting."

The paper, "Radiation-pressure-driven micro-mechanical oscillator," appearing in the July 11 issue of the journal Optics Express, is available on-line at http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-14-5293.



Robert Tindol

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.



Robert Tindol

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."


Robert Tindol

Deep Impact: During and After Impact

PALOMAR MOUNTAIN, Calif. - Astronomers using the Palomar Observatory's 200-inch Hale Telescope have been amazed by comet Tempel 1's behavior during and after its collision with the Deep Impact space probe.

In the minutes just after the impact the comet was seen to increase its near-infrared brightness nearly fivefold. As the event progressed astronomers at Palomar were able to distinguish jets of material venting from the comet's nucleus that have persisted for days.

Early results from the data, in images taken just minutes after impact, showed a possible plume of dust and gas extending outward some 320 km (200 miles) from the comet's center, roughly coinciding with the site of the probe's final demise.

This apparent dust plume has persisted for several nights, allowing astronomers to watch the comet's slow rotation. The night after impact the plume was on the far side of the comet, but was visible again the next evening as the comet's rotation brought it back into view. Two days after impact, the plume was seen again, this time extending about 200 km (124 miles) from the comet's center. According to Bidushi Bhattacharya of the California Institute of Technology's (Caltech) Spitzer Science Center, "This could be indicative of an outburst of gas and dust still taking place near the region of the impact."

"We are very excited by these results. It is a fabulous time to be studying comets," says James Bauer of the Jet Propulsion Laboratory (JPL). "It will be interesting to see how long the effects of the impact persist," he adds.

The images of the comet, obtained by Bauer and Bhattacharya, were sharper than those from most ground-based telescopes because they used a technique known as adaptive optics. Adaptive optics allows astronomers to correct for the blurring of images caused by Earth's turbulent atmosphere, giving them a view that often surpasses those of smaller telescopes based in space.

Using the adaptive-optics technique to improve an astronomer's view is generally only possible when a bright star is located near the object they want to study. On the night of impact there was no bright star close enough to the comet to use. Mitchell Troy, the adaptive-optics group lead and Palomar adaptive-optics task manager at JPL, worked with his team to make adaptive optics corrections anyway. "Through the dedicated efforts of the JPL and Caltech teams we were able to deploy a new sensor that was 25 times more sensitive then our normal sensor. This new sensor allowed us to correct for some of the atmosphere's distortions and significantly improve the view of the comet," says Troy. This improved view allowed astronomers to see the dust and ejected material moving out from the comet's surface immediately following the impact event and again days later.

Earth-based observations from telescopes like the 200-inch at Palomar give astronomers an important perspective on how the comet is reacting to the impact, a perspective that cannot be achieved from the front-row seat of a fly-by spacecraft. Astronomers on the ground have the luxury of long-term observations that may continue to show changes in the comet for weeks to come.

Collaborators on the observations include Paul Weissman (JPL), and the Palomar 200-inch crew. The Caltech-adaptive optics team is made up of Richard Dekany (team leader), Antonin Bouchez, Matthew Britton, Khanh Bui, Alan Morrissett, Hal Petrie, Viswa Velur and Bob Weber. The JPL Palomar adaptive-optics team includes Mitchell Troy (team leader), John Angione, Sidd Bikkannavar, Gary Brack, Steve Guiwits, Dean Palmer, Ben Platt , Jennifer Roberts, Chris Shelton, Fang Shi, Thang Trinh, Tuan Truong and Kent Wallace.

The Palomar adaptive-optics instrument was built and continues to be supported by the Jet Propulsion Laboratory as part of a Caltech-JPL collaboration.

Support for the adaptive-optics research at Caltech's Palomar Observatory comes from the Oschin Family Foundation, the Gordon and Betty Moore Foundation and the National Science Foundation Center for Adaptive Optics.

MEDIA CONTACT: Scott Kardel, Palomar Public Affairs Director (760) 742-2111 wsk@astro.caltech.edu

Visit the Caltech media relations web site: http://pr.caltech.edu/media Images are available at: http://www.astro.caltech.edu/palomarnew/deepimpact.html



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.



Robert Tindol

Preferring a Taste and Recognizing It May Involve Separate Brain Areas, Study Shows

PASADENA, Calif.—Are you disgusted when you hear about Elvis Presley's fried peanut butter 'n 'nanner sandwiches? A new study shows that it could all be in your head. In fact, our taste preferences may have little to do with whether we can even recognize the substance we're eating or drinking.

In the current issue of Nature Neuroscience, California Institute of Technology neuroscientist Ralph Adolphs and his colleagues at the University of Iowa report on their examinations of a patient whose sense of taste has been severely compromised. The patient suffered from a herpes brain infection years ago that left him with brain damage. Today, the patient is unable to name even familiar foods by taste or by smell, and shows remarkably little preference in his choice of food and drink.

According to Adolphs, who is a professor of psychology and neuroscience at Caltech, the subject is a 72-year-old man, known as "B," whose brain infection destroyed his amygdala, hippocampus, the nearby temporal cortices, and the insula, and damaged several other brain structures. As a result, the patient today has a memory span of about 40 seconds, somewhat similar to that of the character in the film Memento.

As a result of his extensive brain damage, B is unable to recognize familiar people and many objects, although his vision and his use of language are unaffected. In terms of taste, he fails to recognize any familiar food items, and could probably outdo even Elvis by wading into a banana and mayonnaise sandwich with gusto.

"Our likes and dislikes in taste stem from both innate and cultural causes," Adolphs explains. "You may like sushi or bitter melon or certain smelly cheeses, whereas other people turn away from these foods in distaste."

The research shows that it may be possible to like or dislike certain foods without being able to recognize them at all, and that different regions of the brain are responsible for these two processes.

To test this hypothesis, the researchers set up an experiment in which B, several other subjects with brain damage, and several normal subjects were all offered salty and sweet drinks. All the subjects drank the sweet drinks and said they enjoyed them, and all with the notable exception of B said they found the saline drink disgusting.

By contrast, B drank the saline solution with a pleased expression, saying it "tasted like pop." However, when he was asked to sip both a salty and a sweet drink and to continue drinking the one he preferred, he chose the sweet one and took a pass on the salty one.

The researchers concluded that B, like most people, has some fundamental preference for sweet drinks over salty ones-which goes far to explain why soft drinks have always been made with sugar rather than salt-even if he is unaware of the identity of either. In sum, it would seem that B has no preference for drinks unless he can compare them within the 40-second span of his memory.

What does this mean for us regular tasters? According to Adolphs, taste information "that is meaningless for an isolated individual stimulus can yield relative values when the taste is structured as a comparison." In other words, there's something in your brain that indeed has a preference for a sweet drink over a salty one, but there's something else in your brain that disgusts you when you're given a salty drink when you know you could've had a cola.

The research was supported by grants from the National Institute of Mental Health and the National Institute of Neurological Disorders and Stroke. The paper's coauthors are Daniel Tranel, Michael Koenigs, and Antonio R. Damasio, all of the University of Iowa's Department of Neurology and Neuroscience.

Robert Tindol

Researchers devise plasma experiment that shows how astrophysical jets are formed

PASADENA, Calif.--Applied physicists at the California Institute of Technology have devised a plasma experiment that shows how huge long, thin jets of material shoot out from exotic astrophysical objects such as young stars, black holes, and galactic nuclei.

Reporting in an upcoming issue of the journal Physical Review Letters, applied physics professor Paul Bellan, his graduate student Gunsu Yun, and postdoctoral scholar Setthivoine You describe how they create jets of plasma at will in an experimental device known as a "planar spheromak gun." The researchers form the jets by sending an intense electric current through a gas to form a plasma, after applying a background magnetic field to the whole system. The magnetized plasma then naturally tends to shoot out of the gun in the form of a long collimated filament.

According to Bellan, his research group is the first to achieve an experimental result showing how astrophysical jets are formed. Theorists have done mathematical modeling and computer simulations to show how known magnetohydrodynamic effects could explain the jet phenomenon, but the Bellan experiment actually creates similar jets in a lab device.

"We're not claiming to make scale models, but I think we've captured the essence of astrophysical jets," says Bellan, who has been working on this and related projects at Caltech since the late 1990s.

Although there are differences between astrophysical jets and the ones created in the spheromak gun, Bellan says there are also important similarities that link the 13-inch-long plasma jets created in the lab to the enormous jets in outer space. The similarity is primarily in the way that the magnetic flux tubes are straightened through a sort of squeezing effect that points to a common collimation process.

Astrophysical jets are accelerated by magnetic forces, but also carry along magnetic fields, the researchers explain. These magnetic fields are frozen into the plasma that makes up the jet and wrapped around the jet like rubber bands around a paper tube. The flowing plasma piles up, much like fast traffic coming up on slower traffic on a freeway, and this pile-up increases the plasma density just like the density of cars increases in a traffic jam.

The frozen-in bandlike magnetic field lines also become squeezed together in this "traffic jam," and so, just like rubber bands piling up on a paper tube, pinch down the diameter of the plasma jet, making it thin and even more dense.

Why do the researchers think this is an accurate portrayal of astrophysical jets? Because this is precisely how they make similar but smaller jets in their experiment.

"Very dense, fast, thin plasma jets observed in our laboratory experiments have been shown to be in good agreement with this picture," explains You.

Bellan says that the research stems from work he and his group have done for years in the formidable and longstanding effort to make fusion power an eventual reality. The current results have implications for the goal of containing the extremely hot plasma required for fusion, as well as for explaining certain exotic events in the cosmos.




Single-Cell Recognition: A Halle Berry Brain Cell

Embargoed for release at 10 a.m., PDT, June 22, 2005

PASADENA, Calif. - World travelers can instantly identify the architectural sails of the Sydney Opera House, while movie aficionados can immediately I.D. Oscar-winning actress Halle Berry beneath her Catwoman costume or even in an artist's caricature. But how does the human brain instantly translate varied and abstract visual images into a single and consistently recognizable concept?

Now a research team of neuroscientists from the California Institute of Technology and UCLA has found that a single neuron can recognize people, landmarks, and objects--even letter strings of names ("H-A-L-L-E-B-E-R-R-Y"). The findings, reported in the current issue of the journal Nature, suggest that a consistent, sparse, and explicit code may play a role in transforming complex visual representations into long-term and more abstract memories.

"This new understanding of individual neurons as 'thinking cells' is an important step toward cracking the brain's cognition code," says co-senior investigator Itzhak Fried, a professor of neurosurgery at the David Geffen School of Medicine at UCLA, and a professor of psychiatry and biobehavioral sciences at the Semel Institute for Neuroscience and Human Behavior, also at UCLA. "As our understanding grows, we one day may be able to build cognitive prostheses to replace functions lost due to brain injury or disease, perhaps even for memory."

"Our findings fly in the face of conventional thinking about how brain cells function," adds Christof Koch, the Lois and Victor Troendle Professor of Cognitive and Behavioral Biology and professor of computation and neural systems at Caltech, and the other co-senior investigator. "Conventional wisdom views individual brain cells as simple switches or relays. In fact, we are finding that neurons are able to function more like a sophisticated computer."

The study is an example of the power of neurobiological research using data drawn directly from inside a living human brain. Most neurobiological research involves animals, postmortem tissue, or functional brain imaging in magnetic scanners. In contrast, these researchers draw data directly from the brains of eight consenting clinical patients with epilepsy at the UCLA Medical Center, wiring them with intracranial electrodes to identify the seizure origin for potential surgical treatment.

The team recorded responses from the medial temporal lobe, which plays a major role in human memory and is one of the first regions affected in patients with Alzheimer's disease. Responses by individual neurons appeared on a computer screen as spikes on a graph.

In the initial recording session, subjects viewed a large number of images of famous people, landmark buildings, animals, objects, and other images chosen after an interview. To keep the subjects focused, researchers asked them to push a computer key to indicate whether the image was a person. After determining which images prompted a significant response in at least one neuron, additional sessions tested response to three to eight variations of each of those images.

Responses varied with the person and stimulus. For example, a single neuron in the left posterior hippocampus of one subject responded to 30 out of 87 images. It fired in response to all pictures of actress Jennifer Aniston, but not at all, or only very weakly, to other famous and non-famous faces, landmarks, animals, or objects. The neuron also (and wisely, it turns out) did not respond to pictures of Jennifer Aniston together with actor Brad Pitt.

In another patient, pictures of Halle Berry activated a neuron in the right anterior hippocampus, as did a caricature of the actress, images of her in the lead role of the film Catwoman, and a letter sequence spelling her name. In a third subject, a neuron in the left anterior hippocampus responded to pictures of the landmark Sydney Opera House and Baha'í Temple, and also to the letter string "Sydney Opera," but not to other letter strings, such as "Eiffel Tower."

In addition to Koch and Fried, the research team included Rodrigo Quian-Quiroga of Caltech and UCLA, Leila Reddy of Caltech, and Gabriel Kreiman of the Massachusetts Institute of Technology.

The research was funded by grants from the National Institute of Neurological Disorders and Stroke, National Institute of Mental Health, the National Science Foundation, the Defense Advanced Research Projects Agency, the Office of Naval Research, the W. M. Keck Foundation Fund for Discovery in Basic Medical Research, a Whiteman fellowship, the Gordon Moore Foundation, the Sloan Foundation, and the Swartz Foundation for Computational Neuroscience.

MEDIA CONTACTS: Mark Wheeler, Caltech (626) 395-8733 wheel@caltech.edu

Dan Page, UCLA (310) 794-2265 dpage@mednet.ucla.edu


New Propane-Burning Fuel Cell Could Energize a Future Generation of Small Electrical Devices

PASADENA, Calif.--Engineers have created a propane-burning fuel cell that's almost as small as a watch battery, yet many times higher in power density. Led by Sossina Haile of the California Institute of Technology, the team reports in the June 9 issue of the journal Nature that two of the cells have sufficient power to drive an MP3 player. If commercialized, such a fuel cell would have the advantage of driving the MP3 player for far longer than the best lithium batteries available.

According to Haile, who is an associate professor of materials science and of chemical engineering at Caltech, the new technology was made possible by a couple of key breakthroughs in fuel-cell technology. Chief among these was a novel method of getting the fuel cell to generate enough internal heat to keep itself hot, a requirement for producing power.

"Fuel cells have been done on larger scales with hydrocarbon fuels, but small fuel cells are challenging because it's hard to keep them at the high temperatures required to get the hydrocarbon fuels to react," Haile says. "In a small device, the surface-to-volume ratio is large, and because heat is lost through the surface that is generated in the volume, you have to use a lot of insulation to keep the cell hot. Adding insulation takes away the size advantage."

The new technology tackles this problem by burning just a bit of the fuel to generate heat to maintain the fuel cell temperature. The device could probably use a variety of hydrocarbon fuels, but propane is just about perfect because it is easily compressible into a liquid and because it instantly becomes a vapor when it is released. That's exactly what makes it ideal for your backyard barbecue grill.

"Actually, there are three advances that make the technology possible," Haile says. "The first is to make the fuel cells operate with high power outputs at lower temperatures than conventional hydrocarbon-burning fuel cells. The second is to use a single-chamber fuel cell that has only one inlet for premixed oxygen and fuel and a single outlet for exhaust, which makes for a very simple and compact fuel cell system. These advances were achieved here at Caltech."

"The third involves catalysts developed at Northwestern University that cause sufficient heat release to sustain the temperature of the fuel cell." In addition, a linear counter-flow heat exchanger makes sure that the hot gases exiting from the fuel cell transfer their heat to the incoming cold inlet gases.

Although the technology is still experimental, Haile says that future collaborations with design experts should tremendously improve the fuel efficiency. In particular, she and her colleagues are working with David Goodwin, a professor of mechanical engineering and applied physics at Caltech, on design improvements. One such improvement will be to incorporate compact "Swiss roll" heat exchangers, produced by collaborator Paul Ronney at USC.

As for applications, Haile says that the sky is literally the limit. Potential applications could include the tiny flying robots in which the defense funding agency DARPA has shown so much interest in recent years. For everyday uses, the fuel cells could also provide longer-lasting sources of power for laptop computers, television cameras, and pretty much any other device in which batteries are too heavy or too short-lived.

In addition to Haile, the other authors are Zongping Shao, a postdoctoral scholar in Haile's lab; Jeongmin Ahn and Paul D. Ronney, both of USC; and Zhongliang Zhan and Scott A. Barnett, both of Northwestern.

Robert Tindol
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