Secrets of the red planet
POSTED 30 MAY 2002
 

RELATED WHY FILES:
The Why Files covered weird "life" on Mars, and on Earth.

The Why Files covers the battle between evolution and creationism.

 

 


In this false-color map of Mars, made by the neutron spectrometer on Mars Odyssey, soil enriched in hydrogen appears deep blue. Some water near the north pole may be hidden by frozen carbon-dioxide. NASA

 

The water planet?
Mars holds more water than Lake Michigan, frozen just below the surface!Scientists have found ice on Mars. The frozen water, whose quantity may equal Lake Michigan, is within a meter of the surface.

The data came from Mars Odyssey spacecraft, which began studying the planet's surface in February. The study was published in the current Science magazine.

"This is really amazing," says chief author William Boynton of the University of Arizona. "This is the best direct evidence we have of subsurface water ice on Mars." Indeed, he added, "what we have found is much more ice than we ever expected."

"The results, even after only a month of mapping observations, are stunning," Dr. James F. Bell, a professor of astronomy at Cornell University, wrote in a commentary in Science.

Map shows band of deep blue at south pole, also patches near north pole.

The water, obviously, could wind up being guzzled by thirsty astronauts, reducing the need to blast heavy slurpees into space. And, if broken down into hydrogen and oxygen, water could fuel the return to Earth.

From a scientific standpoint, the study answers a pesky paradox: How could such a dry planet have so many features, like giant canyons and ancient coastlines, associated with water?

And if Mars was once wet, and warm enough to have liquid water, did it also have life?

Life (?) on Mars
That notion recalls the 1996 finding that a meteorite from Mars had suspicious signs of life. The meteorite was blasted into space by an asteroid, and lay around in Antarctica for some 12,000 years, before being discovered in 1984.

leathery surface with tube-shaped object and some grainsMagnification of "fossils" in the Martian meteorite. NASA.

After inspecting the meteorite, NASA's David McKay and colleagues located tiny carbonate structures and organic molecules that they suspected had been formed by bacteria on Mars more than 1.3 billion years ago, when the Red Planet was much warmer and, presumably, wetter.

The assertion was controversial from the first, and further analyses have fueled the doubters.

The small, round objects that the NASA scientists called fossils of tiny bacteria could not represent life as we know it. Bacteria apparently cannot get that small.

Polycyclic aromatic hydrocarbons may have been found on early Mars, formed through inorganic processes.

The odd-shaped molecules dubbed "worms" look like many structures built by inorganic processes.

"The case has weakened dramatically," meteor scientist Horton Newsome told Science magazine. Numerous researchers spent two years examining the 2-kilogram rock, and, "a number of lines of evidence have gone away."

Brief background blurb
Jeffrey Bada, director of the NASA Specialized Center of Research and Training in Exobiology at the Scripps Institution of Oceanography in California, was the main author of one of the reports questioning the McKay theory. His team looked at amino acids in fragments of the potato-sized meteorite. Amino acids, the building blocks for proteins and enzymes, are essential to all known forms of life.

Rays hit surface, and bounce off, in a diagram Cosmic rays hit Mars, causing gamma rays and neutrons to head back to space where they are measured by Odyssey's gamma-ray spectrometer. The instrument sees telltale signs of the elements in the Martian surface. The large amounts of hydrogen apparently come from water. NASA

Amino acids and some other molecules can form in either of two mirror images. Like your hands, both of these so-called "handed" chemicals look alike. But just as your left hand won't fit a right-hand glove, opposite versions of handed chemicals are different, and biological systems require certain handedness.

Bada found that almost all of those amino acids were lefties. That happens to be true of life on Earth, including other amino acids in the ice where the meteorite was found.

Furthermore, the same four amino acids found in the meteorite were also found in the nearby ice. Scientists prefer simple explanations to complex ones. And Bada says the simplest explanation is that the organic chemicals originated on Earth, not Mars.

Another shoe drops
A second study reinforced that line of thought. McKay had speculated that microbes had formed peculiar mineral grains found inside carbonate structures in the meteorite, which also, he thought, contained organic molecules.

shiny gray-white mineral with orange-yellow center A Mars meteorite sample showing orange-yellow carbonate globules. Courtesy ©UW-Madison John Valley

A.J. Timothy Jull of the University of Arizona looked at carbon isotopes in the meteorite. Isotopes are types of elements containing different numbers of neutrons; an isotope's number denotes its atomic weight.

If the carbonates and the organic material were formed by microbes while on Mars, they should both contain a similar proportion of carbon-13 to carbon-14. But Jull found "the organic material contains carbon-14 and the carbonate doesn't."

Carbon-14 often forms in Earth's upper atmosphere when an energetic particle like a cosmic ray ejects a proton from a nitrogen nucleus. Thus Jull concluded that the carbon-14-less carbonates must have come from "somewhere in space, presumably Mars, and the organic material is a recent addition which took place while the meteorite was sitting on the ice."

Ouch!
Instead of carrying messages from Mars, Jull says the rock went through "several episodes of contamination" by liquids containing amino acids while in Antarctica.

Although the notion that this meteorite carries evidence of life is now gasping for air, the presence of large amounts of water on Mars makes the return of samples from the red planet all the more interesting.

red planet The meteorite may not have carried life, but that does not prove that Mars has always been lifeless. Kinda makes us want to raise a glass...

--David Tenenbaum

 

     

BIBLIOGRAPHY
The Case for Life on Mars, Everett Gibson, Jr., David McKay et al, Scientific American, Dec. 1997, p. 58 ff.

Isotopic Evidence for a Terrestrial Source... A.J.T. Jull et al, Science, 16 Jan., 1997.

Requiem for Life on Mars? Support for Microbes Fades, Richard Kerr, Science, 20 November, 1998, pp. 1398-1400.

Scientists Measuring Martian Ice Detect Oceans' Worth, Kenneth Chang, The New York Times, May 28, 2002.

Search for Endogenous Amino Acids in Martian Meteorite ALH84001, Jeffrey Bada et al, Science, 16 Jan., 1997.

"Distribution of Hydrogen in the Near-Surface of Mars: Evidence for Subsurface Ice Deposits," by W. V. Boynton et al, Science, 31 May 2002.

 

 
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