POSTED 30 MAY 2002
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.
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
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 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
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
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."
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.
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...
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.