[meteorite-list] Hunting Martian Fossils Best Bet For Locating Mars Life

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 22 Feb 2007 23:01:51 -0800 (PST)
Message-ID: <200702230701.XAA29038_at_zagami.jpl.nasa.gov>

College of Liberal Arts and Sciences
Arizona State University
Tempe, Arizona

Media contacts:
Skip Derra, (602) 510-3402
Robert Burnham, (480) 458-8207

Source:
Jack Farmer, (480) 560-1764

Feb. 16, 2007

Hunting Martian fossils best bet for locating Mars life, says ASU researcher

SAN FRANCISCO, Calif. -- Hunting for traces of life on Mars calls for two
radically different strategies, says Arizona State University professor Jack
Farmer. Of the two, he says, with today's exploration technology we can most
easily look for evidence for past life, preserved as fossil "biosignatures"
in old rocks.

Farmer is a professor of geological sciences in ASU's School of Earth and
Space Exploration, where he heads the astrobiology program. He is reporting
on his work today (Feb. 16) at the annual meeting of the American
Association for the Advancement of Science in San Francisco.

"Searching for extraterrestrial life must follow two alternative pathways,
each requiring a different approach and tools," Farmer says. "If we're
looking for living organisms, we are doing exobiology. But if we are seeking
traces -- biosignatures -- of ancient life, it's better to call it
exopaleontology."

Unfortunately, he notes, "for the next 10 or 15 years, technology
limitations will force us down the exopaleontology path." The core issue is
accessibility. "To find living organisms on Mars," says Farmer, "you need to
find liquid water. Because liquid water is unstable on the Martian surface
today, that means going deep into the subsurface."

Water saturates the ground in high latitudes north and south, and around
both poles, only a few inches below the surface, Farmer explains. But this
water remains frozen year round. "Environments with liquid water will likely
lie far deeper, perhaps miles below the surface."

Organisms have been found living in fractured rock, thousands of feet
underground on Earth, Farmer notes. "But with current robotic technology, we
simply can't drill that deep on Mars."

Terrestrial deep drilling requires complex, heavy equipment, plus constant
supervision and troubleshooting by human crews.

Says Farmer, "We'll be lucky if, in the next decade or so, robotic drilling
on Mars reaches a depth of a couple yards."

So where does that leave us in the search for life on Mars? Farmer says our
best choice is to pursue the exopaleontology path.

"Finding the signatures of an ancient Martian biosphere means exploring old
rocks that might preserve traces of life for millions or billions of years,"
Farmer notes. Among the best places to look on Mars, he says, are deposits
left by springs and former lakes in the heavily cratered highlands. "The
rocks there date from a period in Martian history when liquid water was
common at the surface." In fact, says Farmer, conditions on Mars then were
likely similar to those on the early Earth at the time when life began.

"Besides water, life also requires energy sources and organic chemical
building blocks," Farmer explains. "The Mars Exploration Rover Opportunity
found ample evidence for water in ancient rocks at Meridiani Planum, but the
rovers' instruments can't detect organic materials." However, NASA's next
rover, the Mars Science Laboratory, will carry instruments to analyze traces
of organic substances. It is due for launch in 2009.

Recognizing a Martian fossil may be difficult. "We're not talking about
stumbling over dinosaur bones," Farmer says.

Instead, the discovery may involve finding biologically formed structures in
old sedimentary deposits, perhaps like stromatolites found here on Earth.
Stromatolites are distinctive structures that form in shallow oceans, lakes,
or streams where microbial colonies trap sediments to form thin repeating
layers.

Stromatolites also contain microscopic cellular remains and chemical traces
left by the microbes that formed them. Taken together, such structures
comprise the primary record of life in ancient rocks on Earth.

For hunting Martian fossils, says Farmer, we will need robotic microscopic
imagers capable of viewing rocks in many wavelengths as well as seeing
details as small as a hundredth of a millimeter across. Also needed are
organic chemistry laboratories to analyze promising rocks. "That will help
us avoid mistaking non-biological features for biological ones," he says.

Farmer's fieldwork has taken him to extreme microbial habitats in Iceland,
New Zealand, Yellowstone National Park and Mono Lake, Calif. He has sought
to understand how modern microbial communities become preserved as fossils.
Their environments, he notes, span physical and chemical conditions believed
to be representative of early Mars.

"Studying how microbes become fossils is a key step in developing an
effective strategy for exopaleontology," Farmer says. "It will help us find
the best places to explore on Mars and how to look."

IMAGE CAPTION:
[http://www.asu.edu/news/forthemedia/20070214_Biosignatures.htm]
The fossilized remains of Calothrix, a common bacterium in Yellowstone
National Park hot springs, show like branches of a shrub in this microscopic
image. The "branches" are the bacteria's external sheaths, which have been
completely entombed in opal, a mineral that frequently crystallizes from
these hot springs.

Image courtesy of Jack D. Farmer, Arizona State University
Received on Fri 23 Feb 2007 02:01:51 AM PST