[meteorite-list] Controversy Continues: Mars Meteorite Clings to Life - Or Does It?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:02:31 2004
Message-ID: <200203201735.JAA18389_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/solarsystem/mars_meteorite_020320.html

Controversy Continues: Mars Meteorite Clings to Life - Or Does It?
By Leonard David
20 March 2002

HOUSTON, TEXAS - Following years of rigorous study, the inside story of
whether meteorite ALH 84001 - the so-called "Mars rock" - harbors
evidence for past Martian biology remains steeped in debate.

It was a NASA-led research team that announced in August 1996 that the
potato-shaped meteorite found in Antarctica might sport fossilized
bacteria. They argued that "lines of evidence" pointed to the likelihood
that a primitive form of microscopic life that flourished on the red
planet three billion years ago had been found.

Now, fast-forward from 1996 to five-and-a-half years later.

It turns out that rock-solid evidence is hard to come by.

Creature features

The scene is the 33rd Lunar and Planetary Science Conference, held here
March 11-15, and sponsored by NASA and the Lunar and Planetary Institute.
Over the past few years, this annual gathering of top-notch space
scientists has played court to a kind of scientific tennis match about
ALH 84001.

This year was no exception, with pro and con volleys about the true
"message" of the Mars rock still being hotly contested.

"It's a definite maybe," said one meteorite expert, after listening to
over a dozen scientific papers in a session focused on ALH 84001.

The on-going debate now centers on carbonate globules and the presence of
nano-size magnetites within the Mars rock - a purported "biosignature" of
Martian biology. Those opposing this view contend that creature features
in ALH 84001 are not evidence for biogenic activity. Rather, they have
been formed through inorganic means.

Others suggest that any "living proof" of biology in ALH 84001 is little
more than terrestrial contamination - stuff that eked its way into the
meteorite after it came to rest on Earth.

Never the Twain shall meet

"We have concluded there's no way to transport the magnetite into the
Martian carbonates after it fell on Earth," said David McKay, a senior
scientist at NASA's Johnson Space Center. He led the team that first
claimed ALH 84001 had a special story to tell.

McKay said that no plausible scenario could be found that allows any of
these features to be formed in the Antarctic. "We conclude that we cannot
justify the hypothesis that any of the biogenic magnetite is terrestrial
contamination," he said.

Kathie Thomas-Keprta, a research scientist for Lockheed Martin, is also
part of the science team who first brought ALH 84001 to world attention.

Thomas-Keprta began her talk with a power point quote from Mark Twain:
"The scientist will never show any kindness for a theory which he did not
start himself" Her overall message conveyed a "this is my story and I'm
sticking to it" attitude.

"No single process, either inorganic or biogenic, can explain the full
distribution of magnetites observed in ALH 84001 carbonates. We propose
that the origins of magnetites in ALH 84001 can best be explained as the
product of multiple processes," Thomas-Keprta reported.

"This is a dangerous thing to say in this audience - we continue to stand
by our hypothesis," Thomas-Keprta said, reemphasizing her belief that ALH
84001 is rife with biogenic proof of Martian organisms.

Lines of evidence dissected

But for skeptics, ALH 84001 as a showboat of Mars life is a dead issue.

"I think it's over," said Harry McSween, noted space geologist in the
department of geological sciences at the University of Tennessee in
Knoxville.

"Each of the lines of evidence have been systematically dissected. The
only thing that was left was the magnetites. There are just too many
inorganic ways to make the magnetites now - ways that look just like the
magnetites in the meteorite," McSween said.

"I'd love for this life hypothesis to be right. It may well be right for
Mars. I just don't think it's right for this meteorite," McSween told
SPACE.com.

McSween said that the years of debate have been beneficial. Identifying
what kinds of signatures of life are real and can be depended upon is
crucial, particularly when spacecraft missions return the first Mars
samples, or in trying to make on-the-spot judgements via instruments on
the planet.

The Mars rock saga has shown how tricky it is to figure out
biosignatures, McSween said. "A lot of people, including the McKay team,
have done some exquisite work. This is going to be really useful to the
community. This is all valuable stuff," he said.

Scientific punches

ALH 84001 is a very complex rock, loaded with multiple sets of data, said
Everett Gibson, senior scientist and co-leader of the Mars research team
at the NASA Johnson Space Center.

Gibson was also part of the original team that linked the Mars rock with
possible Martian microfossils.

"We think there's a small percentage of the processes recorded in the
rock - twenty-five percent - that may represent the end product of
biological processes. So you have to sort out what the vast majority of
the signatures are, which are the inorganic, normal production of a rock
and other processes on Mars. Biology is a small ingredient in the life of
a planet. And in the case of Mars, it's only a small component, yet it
leaves trace signatures," Gibson said.

Gibson said those who see meteorite ALH 84001 as holding compelling
evidence for Mars life remain on firm footing.

"This is an argument that's difficult for the person on the street to
sort out and understand the subtleties. This is the way science works.
Any radical idea in science is not accepted quickly," Gibson said.

Egos of those studying the Mars rock are getting bruised and scientific
punches and counter punches are being thrown. And still the debate
continues. In terms of being better prepared for handling Mars return
samples in the future, it's a "win-win situation for science," Gibson
said.

But at the end of the conference day, following another rally of research
papers the detective story that is ALH 84001 remains incomplete.

"The evidence for its biological nature is still there. It's strong. It
hasn't been refuted. This hypothesis has been out for five-and-a-half
years. It's still standing," Gibson said.
Received on Wed 20 Mar 2002 12:35:24 PM PST