Scientists announced Wednesday the formation of a NASA task force that will establish how scientists evaluate evidence in the search for extraterrestrial forms of life.
Dr. John F. Kerridge, of the chemistry department at University of California, San Diego, will chair the task force. He said the group will consist of eight to 10 scientists from "a broad spectrum of expertise," including geochemists, biologists and planetary scientists.
The objective of the task force is to determine a set of potential "biomarkers" -- lines of evidence that indicate some form of life or fossilized life -- prior to the completion of a planned sample return mission to Mars in 2008.
"We don't want to have the same kind of controversy surrounding the samples as we've had for the last three and a half years," said Dr. Kerridge, referring to the Alan Hills meteorite, which scientists in 1996 thought might contain fossilized forms of bacteria from Mars.
The task force will have three primary goals: to evaluate and agree upon known terrestrial biomarkers, to identify the ones from that list that may be applicable to Mars and -- the most challenging of the three -- to identify biomarkers that have not been used for Earth, but might possibly be used for Mars.
As it stands, no one really knows in what form extraterrestrial life -- fossilized or otherwise -- will manifest itself. A symposium to lay the groundwork for the task force begins today during the annual meeting of the Geological Society of America, being held this week in Denver, Colo.
The sample return mission will start with a launch in 2003 that will deposit a rover on the martian surface. The rover will drill 20 to 30 pencil-sized core samples, amounting to about a half kilogram of material - roughly a quarter of the total weight of the Alan Hills meteorite. This material will then be returned to Earth by 2008.
Kerridge said NASA wants scientists by then to be able to definitively say which phenomena qualify as reliable biomarkers before using them to conclude the existence of life.
Dr. Andrew Knoll, an astrobiologist at Harvard University, said scientists currently are not certain if a unique pattern found in a meteorite or a rock sample can be considered biological or formed through some other process.
"On Earth, we have biota to give us a template," Knoll said. "But we don't have that on Mars. What we have may not even be the right template to apply to Mars. If we want to have confidence in evaluating biomarkers, we must exclude the possibility that the pattern [we discover] was formed by processes other than life."
Dr. Kerridge hopes to have the task force convened in two to three weeks, and to issue its report to NASA by next January.
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