Caltech Geologists Find New Evidence That Martian Meteorite Could Have Harbored Life

PASADENA—Geologists studying Martian meteorite ALH84001 have found new support for the possibility that the rock could once have harbored life.

Moreover, the conclusions of California Institute of Technology researchers Joseph L. Kirschvink and Altair T. Maine, and McGill University's Hojatollah Vali, also suggest that Mars had a substantial magnetic field early in its history.

Finally, the new results suggest that any life on the rock existing when it was ejected from Mars could have survived the trip to Earth.

In an article appearing in the March 13 issue of the journal Science, the researchers report that their findings have effectively resolved a controversy about the meteorite that has raged since evidence for Martian life was first presented in 1996. Even before this report, other scientists suggested that the carbonate globules containing the possible Martian fossils had formed at temperatures far too hot for life to survive. All objects found on the meteorite, then, would have to be inorganic.

However, based on magnetic evidence, Kirschvink and his colleagues say that the rock has certainly not been hotter than 350 degrees Celsius in the past four billion years—and probably has not been above the boiling point of water. At these low temperatures, bacterial organisms could conceivably survive.

"Our research doesn't directly address the presence of life," says Kirschvink. "But if our results had gone the other way, the high-temperature scenario would have been supported."

Kirschvink's team began their research on the meteorite by sawing a tiny sample in two and then determining the direction of the magnetic field held by each. This work required the use of an ultrasensitive superconducting magnetometer system, housed in a unique, nonmagnetic clean lab facility. The team's results showed that the sample in which the carbonate material was found had two magnetic directions—one on each side of the fractures.

The distinct magnetic directions are critical to the findings, because any weakly magnetized rock will reorient its magnetism to be aligned with the local field direction after it has been heated to high temperatures and cooled. If two such rock fragments are attached so that their magnetic directions are separate, but are then heated to a certain critical temperature, they will have a uniform direction.

The igneous rock (called pyroxenite) that makes up the bulk of the meteorite contains small inclusions of magnetic iron sulfide minerals that will entirely realign their field directions at about 350°C, and will partially align the field directions at much lower temperatures. Thus, the researchers have concluded that the rock has never been heated substantially since it last cooled some four billion years ago.

"We should have been able to detect even a brief heating event over 100 degrees Celsius," Kirschvink says. "And we didn't."

These results also imply that Mars must have had a magnetic field similar in strength to that of the present Earth when the rock last cooled. This is very important for the evolution of life, as the magnetic field will protect the early atmosphere of a planet from being sputtered away into space by the solar wind. Mars has since lost its strong magnetic field, and its atmosphere is nearly gone.

The fracture surfaces on the meteorite formed after it cooled, during an impact event on Mars that crushed the interior portion. The carbonate globules that contain putative evidence for life formed later on these fracture surfaces, and thus were never exposed to high temperatures, even during their ejection from the Martian surface nearly 15 million years ago, presumably from another large asteroid or comet impact.

A further conclusion one can reach from Kirschvink's work is that the inside of the meteorite never reached high temperatures when it entered Earth's atmosphere. This means, in effect, that any remaining life on the Martian meteorite could have survived the trip from Mars to Earth (which can take as little as a year, according to some dynamic studies), and could have ridden the meteorite down through the atmosphere by residing in the interior cracks of the rock and been deposited safely on Earth.

"An implication of our study is that you could get life from Mars to Earth periodically," Kirschvink says. "In fact, every major impact could do it." Kirschvink's suggested history of the rock is as follows:

The rock crystallized from an igneous melt some 4.5 billion years ago and spent about half a billion years on the primordial planet, being subjected to a series of impact-related metamorphic events, which included formation of the iron sulfide minerals.

After final cooling in the ancient Martian magnetic field about four billion years ago, the rock would have had a single magnetic field direction. Following this, another impact crushed parts of the meteorite without heating it, and caused some of the grains in the interior to rotate relative to each other. This led to a separation of their magnetic directions and produced a set of fracture cracks. Aqueous fluids later percolated through these cracks, perhaps providing a substrate for the growth of Martian bacteria. The rock then sat more or less undisturbed until a huge asteroid or comet smacked into Mars 15 million years ago. The rock wandered in space until about 13,000 years ago, when it fell on the Antarctic ice sheet.

Writer: 
Robert Tindol
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Scientists Find "Good Intentions" in the Brain

PASADENA—Neurobiologists at the California Institute of Technology have succeeded in peeking into one of the many "black boxes" of the primate brain. A study appearing in the March 13 issue of the journal Nature describes an area of the brain where plans for actions are formed.

It has long been known that we gain information through our senses and then respond to our world with actions via body movements. Our brains are organized accordingly, with some sections processing incoming sensory signals such as sights and sounds, and other sections regulating motor outputs such as walking, talking, looking, and reaching. What has puzzled scientists, however, is where in the brain thought is put into action. Presumably there must be an area between the sensory incoming areas and the motor outputting areas that decides or determines what we will do next.

Richard Andersen, James G. Boswell Professor of Neuroscience at Caltech, along with Senior Research Fellow Larry Snyder and graduate student Aaron Batista, chose the posterior parietal cortex as the likely candidate to perform such decisions. This is a high-functioning cognitive area and is the endpoint of what scientists call the visual "where" pathway. Lesions to the parietal cortex of humans result in loss of the ability to appreciate spatial relationships and to navigate accurately.

As Michael Shadlen of the University of Washington says in theNature "News and Views" commentary on the latest findings, "Nowhere in the brain is the connection between body and mind so conspicuous as in the parietal lobes—damage to the parietal cortex disrupts awareness of one's body and the space that it inhabits."

It is here, Andersen postulates, that incoming sensory signals overlap with outgoing movement commands, and it is here where decisions and planning occur. Numerous investigations had assumed a sensory map of external space must exist within the parietal cortex, so that certain subsections would be responsible for certain spatial locations of objects such as "up and to the left" or "down and to the right." Previous results from Andersen's own lab however had led him to question whether absolute space was the driving feature of the posterior parietal map or whether, instead, the intended movement plan was the determining factor in organizing the area.

In a series of experiments designed so that the scientists could "listen in" on the brain cells of monkeys at work, the animals were taught to watch a signal light and, depending on its color, to either reach to or look at the target. When the signal was green they were to reach and when it was red they were only to look at the target. An important additional twist to the study was that the monkeys had to withhold their responses for over a second.

The scientists measured neural activity during this delay when the monkeys had planned the movement but not yet made it. What they found was that different cells within different regions of the posterior parietal cortex became active, depending not so much on where the objects were but rather on which movements were required to obtain them. It seems then that the same visual input activates different subareas depending on how the animal plans to respond.

According to Andersen, this result shows that the pathway through the visual cortex that tells us where things are, ends in a map of intention rather than a map of sensory space as had been previously thought. According to Shadlen these results are intriguing because they indicate that "for the brain, spatial location is not a mathematical abstraction or property of a (sensory) map, but involves the issue of how the body navigates its hand or gaze." Andersen feels the study is important because it demonstrates that "our thoughts are more directly tied to our actions than we had previously imagined, and the posterior parietal cortex appears to be organized more around our intentions than our sensations."

Writer: 
Robert Tindol
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Caltech Chemists Design Molecule To Repair a Type of DNA Damage

PASADENA—Chemists have found a way to repair DNA molecules that have been damaged by ultraviolet radiation. The research is reported in the March 7, 1997, issue of the journal Science.

In the cover article, California Institute of Technology Professor of Chemistry Jacqueline K. Barton and her coworkers Peter J. Dandliker, a postdoctoral associate, and R. Erik Holmlin, a graduate student, report that the new procedure reverses thymine dimers, a well-known type of DNA abnormality caused by exposure to ultraviolet light. By designing a synthetic molecule containing rhodium, the researchers have succeeded in repairing the damage and returning the DNA to its normal state.

The research is also significant in that the rhodium complex can be attached to the end of the DNA strand and repair the damaged site even when it is much farther up the helix.

"What I think is exciting is that we can use the DNA to carry out chemistry at a distance," says Barton. "What we're really doing is transferring information along the helix."

A healthy DNA molecule appears something like a twisted ladder. The two "rails" of the ladder, the DNA backbone are connected with "rungs," the DNA bases adenine, thymine, cytosine and guanine, which are paired together in units called base pairs to form the helical stack.

Thymine dimers occur when two neighboring thymines on the same strand become linked together. The dimer, once formed, leads to mutations because of mispairings when new DNA is made. If the thymine dimers are not repaired, mutations and cancer can result.

The new method repairs the thymine dimers at the very first stage, before mutations can develop. The rhodium complex is exposed to normal visible light, which triggers an electron transfer reaction to repair the thymine dimer. The rhodium complex can either act locally on a thymine dimer lesion on the DNA strand, or can be tethered to the end of the DNA helix to work at a distance.

In the latter case, the electron works its way through the stack of base pairs. The repair efficiency doesn't decrease as the tether point is moved away from the site of damage, the researchers have found. However, the efficiency of the reaction is diminished when the base pair stack, the pathway for electron transfer, is disrupted.

"This argues that the radical, or electron hole, is migrating through the base pairs," Barton says. "Whether electron transfer reactions on DNA also occur in nature is something we need to find out. We have found that this feature of DNA allows one to carry out chemical reactions from a distance."

Barton cautions that the discovery does not represent a new form of chemotherapy. However, the research could point to new protocols for dealing with the molecular changes that precede mutations and cancer.

"This could give us a framework to consider new strategies," she says. This research was funded by the National Institutes of Health. Dandliker is a fellow of the Cancer Research Fund of the Damon Runyon-Walter Winchell Foundation, and Holmlin is a National Science Foundation predoctoral fellow.

Writer: 
Robert Tindol
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Question of the Week: Why Does an Engine Cooling System Have a Thermostat, and Hos Does It Relate To the Coolant Flow Rate?

Question of the Month Submitted by Bill McLellan, Pasadena, California, and answered by Melany Hunt, Associate Professor of Mechanical Engineering, Caltech.

The cooling system is an important part of an automobile engine. I've certainly become more aware of this fact after having my car overheat on the Santa Monica Freeway.

The cooling system serves three important functions. First, it removes excess heat from the engine; second, it maintains the engine operating temperature where it works most efficiently; and finally, it brings the engine up to the right operating temperature as quickly as possible.

The cooling system is composed of six main parts—an engine, a radiator, a water pump, a cooling fan, hoses, and a thermostat. During the combustion process, some of the fuel energy is converted into heat. This heat is transferred to the coolant being circulated through the engine by the water pump. Hoses carry the hot coolant to the radiator, where the heat is transferred to air that is pulled past the engine by the cooling fan. The coolant is then carried back to the water pump and recirculated.

When an engine is cold, such as first thing in the morning, the engine operates a bit differently. To maximize efficiency, the engine is designed to warm up quickly. Once the engine reaches the right operating temperature, the engine is designed to be maintained at a stable temperature, which is the purpose of the thermostat. The thermostat is like a valve that opens and closes as a function of its temperature. The thermostat isolates the engine from the radiator until it has reached a certain minimum temperature. Without a thermostat, the engine would always lose heat to the radiator and take longer to warm up. Once the engine has reached the desired operating temperature, the thermostat adjusts flow to the radiator to maintain a stable temperature.

Sometimes, the coolant is so hot that the thermostat opens all the way, making the engine completely dependent on the radiator to keep its temperature stable. As long as there is enough air flow through the radiator, the engine will stay cool. If for some reason the air flow rate is too low, the radiator won't do its job and the engine may overheat. At this point, if the coolant flow rate is increased, the engine will then transfer more heat to the coolant, which will exacerbate the situation. The thermostat flow restriction helps to increase the pressure in the cooling system, which makes it harder for the coolant to boil in the water pump. However, it does little to help the radiator keep the engine cool.

Question of the Week: What Causes a Gene To Mutate or Change?

Submitted by Virginia Salazar, Whittier, Calif. and answered by Dr. Paul Sternberg, Professor of Biology, Caltech

In most cases, the sequence of DNA making up a gene is copied accurately when a cell divides. This accurate process ensures that each cell is like its parent cell. DNA consists of a string of DNA bases, the letters in the genetic alphabet.

The bad news is that DNA is under continual attack by chemicals within the cell that are byproducts of the ordinary workings of each cell; by environmental hazards; by radiation; and by the general tendency for things to break down. Environmental hazards include natural plant products as well as human-made chemicals. These attacks result in a range of problems, ranging from changes of a single DNA letter to a break in the string.

The good news is that cells counter these continual attacks by correcting essentially all the damage, using a host of beautiful molecular machines. But a mutation occurs when a cell fails to repair damage to its DNA, or repairs it incorrectly. When such a cell divides, it passes on the mutated gene to its progeny. Eggs and sperm, which join to form an embryo, are themselves the product of cell divisions and thus subject to errors in the copying of DNA. These mutations are passed on to our children.

Other cells in our bodies are subject to mutation, and mutant cells can become cancerous. Particularly pernicious are mutations that disrupt the ability of a cell to repair its own DNA. Such mutations are in the genes that are responsible for making the repair machinery. When this occurs, the mutant cell will more easily continue to mutate, a disaster in the making!

Writer: 
Robert Tindol
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Question of the Week: How Often Do Meteors Fall To Earth?

Question of the Month Submitted by Bob and Pat Gaskill, Orange County, and answered by Dr. William Bottke, Texaco Prize Fellow, Division of Geological and Planetary Sciences, Caltech.

Meteors and meteorites are small rocky fragments of other planetary bodies that fall to Earth. When they do so, they often produce spectacular audible and visual effects that can be seen from the ground. Meteorites, objects that survive their fiery passage through Earth's atmosphere, are of particular interest to scientists, since they are pieces of planetary bodies (mostly asteroids) for which samples have not yet been obtained through either manned or unmanned space missions. The oldest meteorites are remnants of the very first processes to occur in our solar system 4.6 billion years ago, giving us a glimpse into what conditions were when Earth was formed.

One common class of meteor is called a "fireball," named for the bright, streaming orbs produced when the surface of a fist-sized or larger body is boiled away by friction as it enters Earth's atmosphere. Fireballs decelerate from speeds of about 60,000 m.p.h. to 200 m.p.h. during this passage, often slowing enough at the end so that they literally drop to the ground. Their flight path is similar to a golf ball thrown at an angle into a swimming pool; once the water stops the forward momentum of the ball, it sinks to the bottom of the pool. The meteor is often not strong enough to survive this passage intact, which can make recovery of the fragments difficult.

Fireballs are mostly seen crossing the sky at night, though some are so bright they can be seen during the day. When a fireball is seen, it is usually several miles high. If any surviving meteoritic pieces were to survive to reach the ground, they would probably be over 500 miles from the observer. If enough people see the fireball from separate locations, however, scientists may be able to calculate where the fragments should strike Earth.

Studies indicate that about 25 meteorites weighing more than a fifth of a pound fall on California (or an area of equal size) each year. Three or four of these samples weigh about two pounds and are the size of your fist. Using these values, we can estimate that between 300 and 400 of these larger meteorites have fallen on California since the turn of the century. Most of these rocks, though, have not been found, leaving open the possibility that you yourself may discover one someday.

Caltech Astronomers Obtain the Most Detailed Infared Image of the Environment of an Active Black Hole

TORONTO — Sophisticated imaging techniques applied on the Keck Telescope have uncovered a new structure in a nearby active galaxy.

The image and associated research are being presented today at the semiannual meeting of the American Astronomical Society. Alycia Weinberger, a doctoral student in physics at the California Institute of Technology, and her collaborators have used the computer-intensive technique of speckle imaging and the 10-meter W. M. Keck Telescope atop Mauna Kea, Hawaii, to image the nucleus of NGC 1068.

This galaxy, found in the constellation Cetus at a distance of about 50 million light years, reveals a a bright active nucleus at infrared wavelengths. This nucleus has long been thought to harbor a black hole as its central engine and, because it is bright and nearby, has been intensely studied by astrophysicists.

The accompanying false color image shows an elongated structure, which is over 100 light-years across, centered on a bright point-like infrared nucleus. In contrast, the bright disk of the galaxy NGC 1068 is over 30,000 light-years across at visual wavelengths.

Made at a wavelength of 2.2 microns, Weinberger's near-infrared image has the capability to reveal structures which are only 12 light years across. This is an extremely small distance by galactic standards, as small as about three times the distance between the Sun and its nearest stellar neighbors. Although taken from a ground based observatory, this image has resolution as fine as what the Hubble Space Telescope achieves in the visual part of the spectrum. The space telescope does not currently have an infrared camera, but is scheduled to receive one in 1997. The elongated feature discovered by the Caltech group has not been seen in Hubble's optical images.

There are two very interesting aspects of this image. First, the image is elongated, and second the axis of the emission points in a different direction than previously observed visual emission. The near-infrared light used to make this picture typically traces the distribution of hot dust and cool stars.

However, in NGC 1068, it is very unlikely that there could be dust 100 light-years from the central black hole which would be hot enough to produce the observed emission. Rather, Weinberger says, it is likely that the observed extended near-infrared light is from stars. Furthermore, since it points in a different direction, this newly resolved infrared emission is likely to come from an entirely different source than previously observed visual emission.

It has long been proposed that stellar bars are a way of funneling material to an active nucleus. As gas moves in a non-circular distribution of stars, such as what may be seen in Weinberger's image, it is forced into orbits likely to take it near the central black hole. This provides a continuous mechanism for "feeding" the central engine.

"The significance of this research is that it finds a brand-new feature in this galaxy. And even more, this new feature may provide observational evidence for a theoretically predicted means of channelling material to the black hole on very small scales," Weinberger says. The image is by no means detailed enough to show the in-fall of the matter itself, Weinberger stresses. For this, one would need a resolution of less than a light-year, and there is currently no way to make such finely detailed pictures.

Nonetheless, the quality of this image is unparalleled because it relies on the unique resolving power of Caltech's 10-m Keck Telescope and the technique of speckle interferometry to remove the distorting effects of Earth's atmosphere. With this technique, a series of very rapid exposures are made of the object, freezing the atmospheric distortions that cause stars to "twinkle." Then the distortions are removed in computer post-processing. As the largest infrared telescope in the world, the Keck Telescope provides the best obtainable resolution.

Weinberger is currently completing work on her doctorate. She will continue doing observations to support this research, a part of her thesis. "It will be exciting to look at NGC 1068 with similar resolution in other infrared wavelengths," she says. "The more information we have across the spectrum the more we'll understand about the nature of this extended emission."

Also collaborating in this research are her thesis supervisor, Gerry Neugebauer and Keith Matthews both of the Caltech physics department.

Writer: 
Robert Tindol
Writer: 

Question of the Week: All the Planets Spin West To East, Except One. Why Does It Spin In the Opposite Direction?

Question of the Month Submitted by Michael Dole, Covina, Calif., and answered by Peter Goldreich, Lee A. DuBridge Professor of Astrophysics and Planetary Physics at Caltech.

You're undoubtedly thinking of Venus as the planet that spins east to west. In other words, if you arrived on Venus in the morning, the sun would be in the west and would set in the east. The only thing is that it would set about four Earth-months later! That's because a day on Venus lasts for 243 of our Earth-days.

Actually, you should probably add Uranus to your list of planets in retrograde (or "backward") rotation, because it is tipped more than 90 degrees. The day would be a short one, because Uranus completes a rotation on its axis every 17 hours, which is a pretty typical time for all the gas giants. The Uranian year is 84 Earth years. Over that time there are large seasonal variations at the poles as they alternately point toward and away from the sun.

As a rule, the inner planets (the solid ones) have much longer spin periods. Mercury completes three rotations every time it goes around the sun once because it is in a tidal lock with the sun, in a manner similar to the tidal lock that causes the moon to always face Earth. A day there lasts about 30 Earth-days.

Mars has the same spin period as Earth, but the angle between its spin axis and the axis of its orbital angular momentum is predicted to vary chaotically between about 11 and 44 degrees on a time scale of millions of years. This is due to the gravity of the sun and other planets. So if you go to Mars now, the sun would rise in the east southeast if you landed at a Southern California latitude during the summer. But if you wait a few million years, the planet might be so tilted that the sun would come up a few degrees north of east each morning while you were at that same latitude at the same time of year.

To get back to your question, nobody knows why the planets have the spins they have. It's plausible that the spin rates date back to the formation stage of the solar system, which began about 4.6 billion years ago and lasted about half a billion years. Because fairly big bodies were being gobbled up by the planets that we observe today, the inclinations of the axes as well as the spin rates are probably relics of these collisions.

Probably, both Venus and Uranus originally rotated from west to east, just like the other seven planets. Perhaps the collisions of other bodies with these two planets flipped them over permanently. In the case of Venus, the tidal effect of the sun's gravity also undoubtedly had a profound effect.

Writer: 
Robert Tindol
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Question of the Week: Why Is the Night Dark and Not As Light As the Day?

Submitted by Jim Early, Orange County, and answered by Dr. Roger Blandford, Richard Chace Tolman Professor of Theoretical Astrophysics and Executive Officer for Astronomy; and David Hogg, Caltech graduate student in physics.

A similar question was asked by Shawn McCord, age 8, of Covina.

This is one of the oldest and most fundamental observations in cosmology, known as "Olbers' paradox." After all, if the universe is infinite and filled with an infinite number of stars, shouldn't every line of sight from Earth hit the surface of a star somewhere? Everywhere you look, you ought to be looking at something as bright as the surface of the Sun.

The sky is dark because the universe is of finite age, born roughly twelve billion years ago in the Big Bang. Because light travels at a finite speed, the part of the universe we can observe is not infinite. In fact, the radius of the visible universe is given by the distance light can travel in twelve billion years: twelve billion light years. Not every line of sight hits the surface of a star; in fact most get to the edge of the visible universe without encountering anything at all. So the night sky is dark, to human eyes.

On the other hand, although the night sky looks dark to us, it is actually very bright with microwaves which make up the cosmic background radiation, the relict light from the Big Bang. For the first three hundred thousand years after the Big Bang, the universe was so hot and dense that it was opaque and glowed like a star. Because light travels at a finite speed, objects observed at a very great distance are also being seen as they appeared a long time ago. So the rays of light which come from the edge of the visible universe were emitted when the universe transitioned from its opaque to its transparent state. If the universe were not expanding, this "surface" in time would glow bright like the surface of a star.

However, the universe is expanding, so the light waves are stretched to longer and longer wavelengths as they travel, and are now stretched into microwaves. To an astronomer with a radio telescope that is capable of detecting microwaves, the night sky does indeed appear as bright as the surface of a star—not because the visible universe is infinite and filled with stars, but because, early on, the universe itself shone bright like an immense star.

Question of the Week: Could There Possibly Be New Elements In the Universe That Haven't Been Detected?

Question of the Month Submitted by Rick Conner, Laguna Niguel, and answered by Donald Burnett, Professor of Geochemistry, Caltech.

The answer is yes.

Elements are numbered according to the number of protons they contain. For example, hydrogen, the first element on the periodic table, has one proton. Oxygen has eight, iron has 26, and gold has 79. Uranium, with 92 protons, is the heaviest element that has been detected elsewhere in the universe by astronomers.

The current periodic table contains about 107 elements, but the ones heavier than uranium have been detected only after being artificially produced in the laboratory. Elements 100 through 107 are especially unstable and difficult to make. Only a few atoms of each have been produced, and these are radioactive, decaying in a few seconds or less.

Theoretically, however, elements having atomic numbers in the range of 109 through 114 should be comparatively stable. In fact, one or more of these "island of stability" elements could exist for a year, or perhaps even billions of years, before decaying.

What we do know is that, for the elements below 100, nature has produced all possible stable nuclei. All of the elements can be produced in the burning processes of stars, but many nuclei heavier than iron—and uranium in particular—are made by spectacular processes such as supernova explosions. And since every single element through uranium can be found both on Earth and elsewhere in the universe, the question is whether nature has filled in the elements between 109 and 114 as well.

Many searches have been made, but natural superheavy elements have not been found. This may mean that the lifetimes of the superheavy elements are relatively short, or that concentrations of superheavy atoms are so small that they were missed, or that there is no way to synthesize superheavy elements in stars.

So the final answer to your question will be left for advanced science of the 21st century.

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