Researchers mutate digital organisms

PASADENA-In a study that could point to a new way of predicting what extraterrestrial life might be like, a team of California Institute of Technology, UCLA and Michigan State researchers have shown that "digital organisms" respond to mutations in ways closely resembling the mutations of actual organisms like bacteria, fungi and fruit flies.

In the Aug. 12 issue of the journal Nature, Caltech computation and neural systems researcher Chris Adami and his colleagues explain the results they have obtained by designing computer programs to be digital organisms that can self-replicate, mutate and adapt by a process analogous to natural selection in nature.

In the study, the authors conclude that complex organisms are more robust than simple ones with respect to how significantly the organisms are affected by single and multiple mutations. Further, the study shows that the overall effect of many mutations can actually result in higher fitness of a complex organism than one would predict from multiplying together the effect of individual mutations.

This latter result tracks closely with experiments with actual simple organisms like bacteria, fungi and fruit flies in which frequent interactions among mutations are observed. But Adami says the conclusions are particularly exciting because the "artificial petri dish" approach demonstrates that digital organisms can be used by researchers to answer important biological questions.

"The advantages are that it's very simple, and that it abstracts the system as much as possible," Adami says. "It's very difficult to ask very fundamental questions about life with a living system because the living system is very complex after four billion years of evolution.

"Life on Earth is all due to one event a long time ago," he says. "Everything we see is related to one accident, so if we look back at this, can we learn something about life in general?"

The answer has implications for future searches for life elsewhere in the solar system and universe, because no one really knows exactly how life got started and how it proceeded to grow in complexity. Therefore, no one really knows all the ground rules of life.

"If we go somewhere else, are we going to find life that is similar or totally different? If it's similar but unrelated, then life is perhaps constrained narrowly. But if it's totally different, then maybe life is constrained very loosely."

Adami's program is based on some of the principles that are known about life and assumed likely to be true elsewhere: living systems replicate, they conserve information and they have dynamic properties that differ from other living systems and allow adaptations.

The digital organisms are based on these principles. By building a digital petri dish in which the programs "live," the researchers can allow the programs to live and fill up a niche, interact with each other, mutate and adapt to local conditions, die out, provide opportunities for other organisms to fill a niche-all the things that organisms on Earth really do, but over many eons.

"We can reconstruct the genetic tree, then change the origin of the tree slightly and rerun the entire tape of evolutionary history," Adami says. "If we change just one molecule way back, this can change everything, we discovered."

The question Adami hopes the new article in Nature will help settle is whether running experiments with digital organisms in a computer is really biology, as biologists understand it. There are skeptics, he says, but he nonetheless thinks the method will gain more believers as the work progresses.

Too, it doesn't hurt that a respected biologist with many years of outstanding accomplishments with actual petri dish cultures is now a collaborator.

"Richard Lenski is the world's expert at doing experimental evolution with E. coli," Adami says. "This paper is the first result of the collaboration, in which we repeated an experiment he has already done with E. coli.

"So I think this is the first time we have convinced biologists that artificial life is not just a pipe dream, but is answering some fundamental questions about biology."

In addition to Adami and Lenski, who is with the Center for Microbial Ecology at Michigan State University, the authors are Charles Ofria, who just earned his doctorate at Caltech in computation and neural systems; and Travis C. Collier of the UCLA Department of Organismic Biology, Ecology and Evolution.

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Robert Tindol
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Caltech joins effort to extend capabilities of major observatories

PASADENA—The California Institute of Technology will participate in a multi-institutional effort, funded by the National Science Foundation, to advance the field of adaptive optics, which promises to revolutionize astronomy.

The National Science Foundation's governing body, the National Science Board, has approved a proposal to establish a Center for Adaptive Optics at the University of California, Santa Cruz. As a partner institution, Caltech will bring together faculty from astronomy, planetary science, and physics to advance the use of existing adaptive optics technology at the 200-inch Hale Telescope at Palomar Observatory in California and the two 10-meter Keck Telescopes in Hawaii.

According to Mike Brown, assistant professor of planetary astronomy and leader of the Caltech team, "This effort will breathe new life into ground-based observing by giving us more sophisticated tools to view distant planetary systems." Depending on the size of the telescope, adaptive optics technology will make images 10 to 20 times sharper, giving scientists a much better view of space. "We plan on making Palomar the best at seeing very faint things next to very bright things, possible indicators of planetary systems. We can learn and experiment at Palomar, then utilize Keck for the really big discoveries."

Very few astronomers have any experience using adaptive optics. "We're hoping to quickly learn how to optimize the technology currently available and pass on that knowledge to other scientists. I expect this to bring about some exciting discoveries," said Brown.

Adaptive optics is a method to actively compensate for changing distortions that cause blurring of images. It is used in astronomy to correct for the blurring effect of turbulence in the earth's atmosphere. For astronomers, adaptive optics can give ground-based telescopes the same clarity of vision that space telescopes achieve by orbiting above the earth's turbulent atmosphere.

Astronomers have already started to reap the benefits of applying adaptive optics to their research. A team headed by Dr. Richard Dekany at the Jet Propulsion Laboratory recently conducted a highly successful first test of an adaptive optics system on the 200-inch Hale Telescope at Palomar Observatory. Enhanced high-resolution images of excellent quality were obtained of the ring system of Uranus and of the Lagoon Nebula.

The 27 partner institutions of the Center for Adaptive Optics will include Caltech, UC Berkeley, UC San Diego, UCLA, UC Irvine, the University of Chicago, the University of Rochester, the University of Houston, Indiana University, Lawrence Livermore National Laboratory, and 17 other national laboratory, industry, and international partners.

The center will provide the sustained effort needed to bring adaptive optics from promise to widespread use. It will conduct research, educate students, develop new instruments, and disseminate knowledge about adaptive optics to the broader scientific community.

Caltech participants will include Shri Kulkarni, Chuck Steidel, Mark Metzger, and Keith Matthews from astronomy, and Christopher Martin from physics.

Palomar Observatory is located near San Diego, Calif., and is owned and operated by Caltech. Caltech and the University of California jointly operate the W. M. Keck Observatory, which houses the world's two largest optical and infared telescopes and is located on Mauna Kea, Hawaii.

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Sue Pitts McHugh
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Advanced networks and ubiquitous computing to be the focus of new technology center

PASADENA-The David and Ellen Lee Family Foundation has donated $10 million to the California Institute of Technology for a center to improve computer networking through innovations such as wireless links.

The center will include broad participation from Caltech researchers in a variety of disciplines, from electrical engineering, computer science, and applied physics to economics. The center will develop research programs in advanced networking, sponsor seminars and cross-disciplinary teaching programs, develop technology exchange programs with industry, and encourage entrepreneurship in the area of advanced networking.

The new campus facility will be named the Lee Center for Advanced Networking, according to Caltech president David Baltimore.

"Our goal is to create new communication technologies that will help change the world," Baltimore says. "The generosity and vision of David and Ellen Lee have made it possible for Caltech to become a leader in advanced computer networking."

Caltech provost Steve Koonin says the new center will help revolutionize the ways in which information moves from place to place. "With this donation, we will develop information space where people can communicate, regardless of where they are geographically, or whether they are mobile or stationary."

The center will focus on creating a worldwide distributed computing system that connects people and appliances through wireless and high-bandwidth wired channels, Koonin says.

Dr. David L. Lee is president and chief operating officer at Global Crossing and holds a doctorate from Caltech in physics with a minor in economics.

"Deregulation in the telecommunications industry and breakthroughs in optronics technologies have caused fundamental, structural changes in global communications," said Lee. "New types of global networks are being built at a fraction of the cost of the legacy networks they replace. A world of seamless, ubiquitous connectivity is now within our reach, with a networked computer in almost every human tool and habitat. It is my hope that this new center will help realize that new future."

"The traditionally interdisciplinary nature of Caltech will help develop unique research and teaching programs that span all the components of engineering, sciences, and the social sciences," says Caltech Professor of Engineering David Rutledge, who will be charter director of the center. "The research will span everything from optical fiber and silicon substrates, to applications such as e-commerce, e-service, and distance learning."

E-service, for example, would expand communications far beyond the capabilities of standard e-mail. An automobile might be installed with wireless communication so that an automated message is sent to emergency services when the car's air bag goes off in an accident.

Virtual learning and long-distance collaboration, too, would greatly benefit from improved networking capabilities. In an age when social and market forces are making the boundaries between workplace and home more vague, the new technologies could allow parents to do their jobs while at home with much greater ease than currently possible. Multinational collaborations would be easier, and state-of-the-art teaching at remote facilities would be improved.

Caltech faculty to initially be associated with the center:

-David Rutledge, director, Lee Center for Advanced Networking; and executive officer for electrical engineering;

- Jehoshua Bruck, professor of computation and neural systems and electrical engineering;

-Mani Chandy, Simon Ramo Professor of Computer Science and executive officer for computer science;

-John Doyle, professor of control and dynamical systems and electrical engineering;

-Michelle Effros, assistant professor of electrical engineering;

-Ali Hajimiri, assistant professor of electrical engineering;

-Robert McEliece, Allen E. Puckett Professor and professor of electrical engineering;

-Charles Plott, Edwin S. Harkness Professor of Economics and Political Science and director of the Caltech Laboratory for Experimental Economics and Political Science;

-Kerry Vahala, professor of applied physics.

With the support of the grant announced today, Caltech will also recruit new faculty members to expand the scope and depth of the Center's research capabilities.

 

Writer: 
Robert Tindol
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Many life-bearing planets could exist in interstellar space, according to Caltech planetary science professor

PASADENA-Long ago in a solar system not at all far away, there could have existed about five to 10 Earth-like planets in Jupiter-crossing orbits.

These planets today could harbor life somewhere in interstellar space, according to a planetary scientist at the California Institute of Technology.

In the July 1 issue of the journal Nature, Caltech professor Dave Stevenson says in a new study that such objects could be life-sustaining due especially to the molecular hydrogen they accreted when the solar system formed long ago.

Called "interstellar planets" because they would exist between the stars but no longer in orbit around an original parent star, they have never been directly observed or proved to even exist. But based on what scientists know about the way matter should fall together in forming a solar system, such Earth-like planets could definitely have been formed.

Over a period of several million years, one of two things happened to these planets: either they slammed into Jupiter and made it even bigger, or else they came so close to Jupiter that they were catapulted by gravity completely out of the solar system, never to return.

Because these bodies formed when the solar system was permeated with hydrogen gas, they retained a dense atmosphere of hydrogen, allowing them to have surfaces with temperatures not too different from Earth, and possibly water oceans.

Stevenson writes that in the absence of sunlight, the natural radioactivity inside an Earth-like planet would only be sufficient to raise the radiating temperature of the body to 30 degrees above absolute zero (that's about minus 400 Fahrenheit). But the expected dense hydrogen atmosphere would prevent the surface from radiating effectively-just like the greenhouse effect on Earth, but more so.

As a result, the surface could have a similar temperature to the current Earth surface, allowing water oceans and a surface pressure similar to that at the bottom of Earth's oceans. For this to happen, the interstellar planet would probably need to be at least half Earth's mass.

Therefore, the energy source would be much the same as that which drives geothermal energy and plate tectonics on Earth.

It is not known whether geothermal heat alone is sufficent to allow life to originate, and the amount of energy is small compared to sunlight, suggesting that the amount of biological activity would also be small. But the existence of life in such an environment would be of great interest even if the mass of living matter were small.

The heat energy, and especially variations in temperature, could potentially allow life to get going, Stevenson says.

"I'm not saying that these objects have life, but everyone agrees that life requires disequilibrium," he says. "So there has to be a way to get free energy, because that's what drives biochemical processes.

"These objects could have weather, variations in clouds, oceans...even lightning."

If life exists on such objects, an open question is how complex it could be, Stevenson says. "I don't think anyone knows what is required to drive biological evolution from simple to very complex systems."

These interstellar wanderers could also have arisen as a natural outcome of the formation of stars, and not just during the formation of the system we live in. In either case, such planets cannot be seen with present technology because they are so dark and cold-at least from Earth's vantage point.

Although these bodies may have warm surfaces, they would appear to us as very weak emitters of long-wavelength infrared radiation, much below current detection limits.

The best bet for even demonstrating that interstellar planets exist is to have some programmed search for occultations, he says. In other words, the object might pass occasionally in the direct line of sight between Earth and a star, and if instruments were watching, the light of the star might dim or even flicker out for a time.

Programs like this are already advocated for the purpose of looking for planets in orbit around other stars. But looking for interstellar planets would be even harder.

"All I'm saying is that, among the places you might want to consider for sustainable life, you might eventually want to look at these objects. They could be the most common location for life in the universe."

Writer: 
Robert Tindol

Caltech researchers use the "unnatural selection" of directed evolution to alter a bacterial enzyme

In a novel process that makes the evolution of species look like an engineering design contest, California Institute of Technology scientists have forced a bacterial strain to "evolve" a beta caratenoid enzyme . The evolved enzyme can carry out reactions that normally require other proteins and expensive agents. These reactions are important for making drugs and chemicals.

The enzyme, called a cytochrome P450, is one of a class of enzymes that inserts oxygen atoms into a huge number of compounds, according to Caltech chemical engineering and biochemistry professor Frances Arnold. In an article appearing in the June 17 issue of the journal Nature, Arnold and her team demonstrate an evolutionary process to alter the enzyme and overcome several of the natural limitations that make it inefficient and expensive to use. "The P450s do some great chemistry, but they are complex and ill-behaved," says Arnold, who helped pioneer directed evolution some years ago. "We hope to create stable P450s that need no expensive external cofactors to work. We'd like to pare them down to the absolute minimum and see how well they can do. They may well be much better catalysts without all the fancy machinery."

Nature helps these enzymes along by providing a retinue of protein assistants and complex chemicals that are either impossible or very expensive to reproduce outside a cell. In the Nature paper, the Arnold team reports the laboratory evolution of a P450 that no longer needs any of this help to catalyze its reaction.

Directed evolution has been heralded recently as a means of creating new enzymes and even whole organisms with new or vastly improved characteristics. In contrast to natural evolution, in which the survival of the fittest dictates the direction of change, directed evolution engineers enzymes for specific purposes. These purposes may have nothing to do with what the enzymes do in their natural organisms. For example, the enzymes may be better suited for removing laundry stains, or they may be used to treat diseases.

In directed evolution, the scientists dictate which enzyme characteristics will be selected in each generation, very much the way plant breeders use mutation and selective breeding to create new corn varieties or animal breeders have introduced new varieties of cattle or sheep.

In the case of the P450 enzymes, Arnold and her team wanted an enzyme that would work without any additional help. To do this, they made use of a known feature of the P450s—that hydrogen peroxide could support the reaction in the absence of the helper proteins and cofactor. Their goal was to evolve what Arnold calls this "biochemical oddity" to make it the primary pathway for the enzyme to work.

Arnold is interested in creating enzyme catalysts that could be used to manufacture drugs and chemicals. "The ideal is a rock-stable, very fast, very active enzyme that you could put in a bottle," she says. "Over the next five to 10 years, we're aiming at enzymes that the chemical industry could use." These improved enzymes could also perhaps lead eventually to new technologies that remove toxic wastes in soil or water.

"In this paper, we present the results of two generations, which makes the enzyme 20 times better than it originally was," she says. "We don't know how far we'll be able to go. But we hope that 10 more generations could result in something remarkably good. With other enzymes, for example, we have seen improvements of 500-fold over 10 generations."

Arnold's procedure for directed evolution is to first target an interesting enzyme. In the case of the current paper, the enzyme is from Pseudomonas putida, a bacterial strain that uses the P450 enzyme as a sort of "digestive aide" to eat camphor that is found in soil. The researchers then take the gene that codes for the enzyme and create millions of mutants, which they put back into a bacterial "workhorse" that generates the mutant enzymes. The scientists then screen these mutants for the desired qualities.

The best candidates from that generation can either be "bred" together to obtain further improvements, or the process can be started over again with new mutations.

Arnold says that each generation of the P450 enzyme takes about a week or two. Practically, a total effort in directed generation takes at least several months.

The other authors of the paper are Hyun Joo and Zhanglin Lin, both postdoctoral scholars in chemical engineering at Caltech.

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Robert Tindol
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Lack of Energy Makes Life on Europa Unlikely, Caltech Study Concludes

Embargoed for Release at 3 p.m. Thursday, June 3, 1999

PASADENA—Future space travelers to the watery Jovian moon Europa should probably leave their fishing tackle at home. A new study conducted by California Institute of Technology and Jet Propulsion Laboratory scientists shows that the Europan ocean is unlikely to harbor any life form more complex than single-celled organisms—and maybe not even that.

In this week's issue of the journal Science, Caltech geobiologist Eric Gaidos and coauthors Kenneth Nealson and Joseph Kirschvink show that nearly all forms of energy used by life on the Earth are unavailable to the organisms that might live beneath Europa's surface ice layer.

According to Gaidos, "One must be careful when doing comparative planetology. It is not a safe assumption to use Earth as an analogy. A liquid-water ocean on Europa does not necessarily mean there is life there."

On Earth, chemical energy is derived either from sunlight by means of photosynthesis or from the oxygen that is a byproduct. This oxygen reaches even the exotic animals inhabiting the super-hot volcanic vents in the deep sea that were discovered 20 years ago.

Even for the organisms living under ice sheets on Earth, the system is not closed. Energy from outside is available for the organisms underneath.

Unlike Earth, Europa is a closed system. The ice layer cannot be penetrated by sunlight and the only available energy in the system comes from within. This study shows that the energy available is very small compared to levels used by organisms on the Earth. It seems very unlikely that multicellular life could survive, and the lack of energy puts constraints on the likelihood of finding even hardy single-celled organisms.

Gaidos uses the analogy of an energy waterfall. "Chemical energy is falling from a high state to a low state just as water falls due to gravity. Life acts as a waterwheel in this process and harnesses the energy. However, without a source of chemical energy, the waterwheel stops."

Kirschvink adds, "Earth has a lot of metabolic energy available for life, but if you shut off the source, you shut off the system."

The study doesn't completely rule out the possibility of life, however. Gaidos says the study "assumes that the life we look for is based on the same energy sources used by life on Earth.

"The study puts limits on what life is possible," says Gaidos. "Complex life is very unlikely, but there are other possible alternatives for simple organisms to acquire the necessary energy."

One such possibility is that the organisms derive the necessary biochemical energy from oxidized iron (rust) that may exist under the ice. Other possibilities may exist, so long as there is a source of energy and life can insert its waterwheel at some point in the system.

"But we are talking about very simple organisms that can live on these energy sources. These are not multicellular creatures," Gaidos says.

Only the future will reveal what scientists might find under the ice of Europa. But we do know that no fish will be biting.

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Robert Tindol
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New digital sky survey uncovers rare celestial objects

CHICAGO—A large new digital sky survey has been used by astronomers at the California Institute of Technology to discover distant quasars and other rare types of cosmic objects, including mysterious new objects of an unknown nature.

These results are being reported today at the meeting of the American Astronomical Society in Chicago.

The Caltech team, led by S. George Djorgovski, professor of astronomy, made the discoveries in an initial scientific exploration of the Digital Palomar Observatory Sky Survey (DPOSS). The survey, now nearing completion, covers the entire northern sky in three colors, and it is based on a photographic sky atlas (POSS-II) produced at Palomar Observatory.

The final product of the survey is the Palomar-Norris Sky Catalog, which will contain information on over 50 million galaxies and about two billion stars. It will be made available to the general astronomical community, beginning a few months from now.

When complete, DPOSS will contain several terabytes of information (a terabyte is 8 trillion bits, or about the amount of information contained in two million thick books). This is also over a thousand times larger than the amount of information in the entire human genome.

Comparable amounts of data are now being produced by several other digital sky surveys, including the Two-Micron All-Sky Survey (2MASS) in the infrared wavelengths, the forthcoming Sloan Digital Sky Survey (SDSS), which, like DPOSS, will cover the visible light part of the spectrum, and several NASA missions.

Other projects of a similar scope are now under way or are being planned.

"This is the dawn of the new era of information-rich astronomy," says Djorgovski. "This unprecedented amount of astronomical information will enable scientists and students everywhere, without access to large telescopes, to do first-rate observational astronomy."

Surveys like DPOSS can be used to study the universe in a systematic manner—for example, to probe the large-scale structure in the distribution of galaxies in some detail. But they can also be used to discover rare, or even previously unknown types of astronomical objects: the sheer numbers of detected sources make it possible to find objects that are one in a million or even one in a billion—an astronomer's needle in a digital haystack.

Caltech astronomers did exactly that in their initial scientific verification tests of the DPOSS data. The group used novel techniques to search the data for star-like objects with colors unlike those of the ordinary stars.

Some of these are types of objects they expected to find: for example, very distant quasars, seen at the time when the universe was less than 10 percent of its present age. Such quasars are valuable probes of the early universe and galaxy formation. The Caltech team has so far identified over 70 of them, more than the number found by all other groups in the world combined.

Perhaps even more interesting are surprises, unexpected findings of anomalous objects. The Caltech team has one such object whose nature is still unknown.

"It has a spectrum unlike anything else I have ever seen," says Djorgovski. "We have combed the literature and asked all kinds of experts, but no one can tell us what it is. It is the first one of something new—and a complete mystery to us."

Another discovery is objects that can vary in brightness by a large factor. Since the photographs used in DPOSS are taken at different times with different filters, objects that are much brighter at one time would stand out as having peculiar colors. One such discovery is a starlike object which is associated with an extremely faint galaxy.

When the survey photograph was taken, the object was several hundred times brighter than the galaxy itself, perhaps a hundred times brighter than a supernova explosion. Astronomers speculate that it may have been associated with an undetected gamma-ray burst, but it could also be something even more strange and previously unseen.

Astronomers at Caltech and elsewhere are discussing the concept of the future National (or Global) Virtual Observatory, to be built in cyberspace rather than on some mountaintop. This would be a way to organize and combine many of the large new and forthcoming sky surveys and other astronomical data, to make them accessible over the Web, and to provide novel data-mining tools for their scientific exploration.

Astronomers and computer scientists are now starting collaborations to make this vision a reality. This would be a new way of doing astronomy, with a computer and a rich data archive, rather than with a telescope.

"We are really only beginning to explore the universe in some detail. There must be many wonderful new and unexpected things out there, waiting to be discovered, and large sky surveys are the best way to find them," concludes Djorgovski.

In addition to Djorgovski, the Caltech team includes postdoctoral scholars Stephen Odewahn and Robert Brunner, graduate student Roy Gal, and several Caltech undergraduates. Professor of Physics Tom Prince is also one of the leaders of the effort to create the Virtual Observatory. The work on the DPOSS survey is supported by a grant from the Norris Foundation and by other private donors.

Writer: 
Robert Tindol
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Mars Global Surveyor's triumphs follow recovery from ill-fated earlier mission

PASADENA—Arden Albee is often asked how it felt to lose the Mars Observer.

Albee was project scientist of the ill-fated space probe that somehow lost its way in the depths of space in 1993. On its final approach to Mars, scientists lost contact and never heard or saw anything of the spacecraft again. To this day, neither Albee nor anyone else is certain what happened.

"Our suspicion is that, in the process of pressurization, there was a rupture in the lines that set it spinning," says Albee, a professor of geology and planetary science at the California Institute of Technology and longtime collaborator on Jet Propulsion Laboratory planetary missions.

"Mars Observer probably didn't blow up, but we were never able to figure out where it might be because we didn't know if it got captured by Mars," he says. "If it did, then it could be in a Martian orbit; if not, then it's in a sun orbit. But we searched for it in both orbits without luck."

The loss was extremely disappointing to the planetary science community. Had Mars Observer been successful, the spacecraft would have mapped the surface of the Red Planet and sent back a huge amount of data—far more data than had ever been sent back from Mars by all interplanetary probes combined, since the advent of the space program.

Certainly, many scientists would have been in despair after seeing two decades of their life's work evaporate. But Albee in particular and NASA scientists in general are different.

"When we lost Mars Observer, we were so busy putting together the pieces that we didn't really have time to get overly depressed," he says. "For one thing, we weren't immediately sure that the mission was permanently lost. And also, the next launch opportunity was the next fall, so the question was immediately whether we could recover in time to launch another spacecraft during that opportunity.

"There was a fair amount of despair, obviously, but we had a lot of other things to do."

As it turned out, Albee and the hundreds of other scientists, engineers, technicians, and support staff who worked on Observer decided against launching again in 1994. But another window of opportunity opened in December 1996, and this time they were ready with Mars Global Surveyor.

Albee was named project scientist of Global Surveyor, and out of the spare parts of the ill-fated Observer mission came the beginnings of a more compact, more cost-effective mission that has already brought back a tremendous amount of scientific data. In fact, by the time the mission is completed in a couple of years, Global Surveyor will fulfill Observer's original promise of returning more planetary data than all the other missions to date combined.

The Mars Global Surveyor mission, like the highly visible Pathfinder mission of 1997, is an embodiment of the new NASA mantra "faster, better, cheaper." About a ton in weight and the size of an office desk, the Global Surveyor orbiter is bigger than the little Pathfinder rover that so captured the public's imagination on Independence Day 1997. But Global Surveyor is designed to send back vastly more data and perform considerably more science over a much longer period of time.

Very soon after the spacecraft went into Martian orbit, Global Surveyor captured, for the first time, the start of a major dust storm on Mars and followed it through its development and demise.

This and other early accomplishments came at a time when Global Surveyor personnel were undoubtedly feeling a nauseating sense of déjà vu. Early on, the spacecraft developed a glitch when it first began tightening up its orbit.

Global Surveyor, to be "faster, better, cheaper," had been set on a course that took it initially into a huge sweeping elliptical orbit of Mars. On its near approach in each orbit, the probe was to dip into the upper atmosphere of Mars in a maneuver known as aerobraking, which would effectively slow the probe down and eventually place it into a near-circular orbit. But a solar-panel damper failed early in the mission, and damage to the solar panel forced the team to slow down the rate of the aerobraking, and the actual mapping mission only got under way this year.

A couple of other annoying glitches have come and gone, including an antenna stoppage a few weeks ago, and a burn that didn't work quite right. But all in all, Global Surveyor has already turned out to be a very good consolation for those who would have benefited from the data returned by Observer.

The Mars Global Surveyor team announced early in the mission that the on-board magnetometer shows Mars to have a more complex magnetic field than once thought. But results published earlier this year showed that Mars once had a magnetic field even stronger than that of Earth.

This is important because many scientists think a strong magnetic field may be crucial for the evolution of life on a planet, because without it the surface is constantly bathed in strong radiation that would kill most life forms that we know of. Moreover, atmospheric constituents like oxygen and water tend to be "sputtered" away by the solar wind and cosmic rays.

The magnetometer has also recently shown the presence of magnetic stripes that show similarities to stripes that occur on the ocean floor on Earth. It is tempting to conclude that their origin was similar, but this is not yet certain.

The mapping mission is working so well that scientists not only have new knowledge about the surface of Mars, but also vastly improved meteorological understanding. The instruments are monitoring water-ice clouds, carbon dioxide clouds, and dust storms—all highly variable and localized atmospheric phenomena.

Further, the knowledge obtained about Martian weather could perhaps even provide new insights on the nature of weather on Earth.

"At this point, we basically know the topography of Mars, in a sense, better than we know that of the continents of Earth," Albee says.

The basic shape is that of a triaxial ellipsoid with the topography imposed upon it.

Whatever the remaining two years hold for Global Surveyor, Albee says this is probably his last space mission. A Caltech professor since 1959, Albee was originally a geologist, but got involved in space exploration while investigating the lunar samples returned by the Apollo missions of the late 1960s and early 1970s.

Albee got more and more involved in planetary science as time went on. He was involved in the Viking mission to Mars toward its end in the mid-1970s, and in 1978 was named chief scientist at the Jet Propulsion Laboratory. He served until 1984, when he became Caltech's dean of graduate studies—a position he holds to this day, in addition to his ongoing work as a JPL project scientist and a Caltech professor.

"I think I'll let the new generation go back to Mars," he says, adding that the future promise of breakthroughs such as extraterrestrial sample returns will provide strong motivation for his successors.

As for his unflappable demeanor during the Mars Observer loss, Albee sums it all up in a single sentence:

"It's called optimism."

Writer: 
Robert Tindol
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Aeronautics researchers generate cracks that move as fast as the speed of sound, and resemble certain earthquake shear ruptures

PASADENA-When a brittle material breaks, the resulting cracks tend to spread quite rapidly. Anyone who has inadvertently subjected a favorite vase to "floor stress" can attest to this.

But exactly how fast a crack can move has been a subject of debate for some time. To understand how fast is fast, one has to know how quickly stress waves spread. In a solid material, waves spread with two speeds-the slower shear waves move at the shear wave speed, and the faster pressure waves move at the pressure wave speed, also commonly known as the speed of sound in the material.

The researchers who specialize in the topic have thought that cracks move at speeds substantially slower than either of these wave speeds in the material (usually less than 20 percent of the speed of sound).

But new work from California Institute of Technology researchers shows that a certain type of crack can exceed the shear wave speed through the material, creating a sort of "sonic boom," and can almost reach sound speed.

According to Ares Rosakis, professor of aeronautics and applied mechanics, such a crack (called a shear crack) can be generated under controlled circumstances and photographed with ultrahigh-speed equipment capable of taking two million photographs in a second. The pictures show a crack with angled shock waves (Mach cones) that closely resemble photographs of a supersonic bullet breaking the sound barrier.

Click here to view or download the high speed photographs showing the propegation of shear cracks (QuickTime format, 2MB)

This result has practical applications, Rosakis says, because there is reason to believe that certain earthquakes can arise from similar shear breakages. A better understanding of the way in which these cracks get rolling could help seismologists with their models of earthquakes along shear faults, Rosakis believes.

To test the idea, Rosakis and his graduate students Omprakash Samudrala and Demirkan Coker bonded two sheets of a clear polyester material called "Homalite." They introduced a notch along the bond line, and rammed the bottom sheet from the side with a steel projectile moving only at 25 meters per second (56 miles per hour). High-speed photographs of the event showed a shear crack starting from the notch tip and accelerating almost up to the sound speed in the material.

The Rosakis team used this particular setup because a fault zone itself is the weak link between two planes. So if the shearing force along a fault plane indeed sets up shear cracks, then the act of breaking two weakly bonded Homalite plates by sliding them apart would be very similar dynamically.

The high-speed photographs indeed show that shear cracks propagate along the bond line at about 2,200 meters per second (5,000 miles per hour). Further, the Mach cones were clearly visible because the cracks were outrunning material shear wave speed, just as a bullet from a high-powered rifle outruns the speed of sound in air. In fact, these shear cracks are faster than speeding bullets and also faster than the fastest supersonic jet planes!

"I believe processes like that have to do with certain events that may happen in the earth's crust. They may also be very relevant to the way that layered solids or composites, involving bonds, fail when subjected to impact loading," says Rosakis. "This is the first lab demonstration that shows these phenomena are possible."

The work is being published this week in the May 21 issue of the journal Science. Samudrala and Coker, both Caltech graduate students in aeronautics, are the other authors of the paper.

This work has been sponsored by the Office of Naval Research and the National Science Foundation.

Writer: 
Robert Tindol
Writer: 

A unique class of neurons in humans and apes that may participate in cognition, volition, and self-awareness discovered by researchers

PASADENA-Clusters of large neurons found exclusively in the brains of humans and other primates closely related to humans may provide these species with enhanced capacities for solving hard problems, as well as for self-control and self-awareness.

In the April 27 issue of Proceedings of the National Academy of Science, neurobiologists Patrick Hof from Mount Sinai and John Allman from Caltech and their colleagues have found an unusual type of neuron, that is likely to be a recent evolutionary acquisition.

The neurons in question are spindle-shaped cells, which are almost large enough to be seen with the naked eye. Their location in the brain is in the frontal lobe near the corpus callosum, which connects the two halves of the brain.

Allman, the Hixon Professor of Psychobiology and professor of biology; Hof; and their team studied 28 different species of primates and found the spindle neurons only in humans and very closely related apes. The concentration of spindle neurons was greatest in humans, somewhat less in chimpanzees, still less in gorillas, and rare in orangutans.

According to Allman, "This declining concentration matches the degree of relatedness of these apes to humans." There were no spindle cells in gibbons, which are small apes, or in of any of the other 22 species of monkey or prosimian primates they examined. The spindle cells were also absent in 20 nonprimate species examined including various marsupials, bats, carnivores and whales.

The cells in question are found in an area of the brain already linked to psychiatric diseases. According to Allman, "In brain imaging studies of depressed patients, there is less neuronal activity in the region and the volume of the area is smaller. The activity of the area is increased in obsessive compulsive patients."

The activity of the area has been shown to increase with the difficulty of the cognitive task being performed. This suggests that the area enhances the capacity to do hard thinking. Activity is also increased when a subject withholds a response or focuses its attention, suggesting the area is involved in self-control.

Furthermore, the spindle neurons themselves are especially vulnerable to degeneration in Alzheimer's disease, which is characterized by diminished self-awareness. From this Allman suggests, "Part of the neuronal susceptibility that occurs in the brain in the course of age-related dementing illnesses may have appeared only recently during primate evolution."

Writer: 
Robert Tindol
Writer: 

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