[meteorite-list] Rocks From Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:11 2004
Message-ID: <200106041629.JAA11744_at_zagami.jpl.nasa.gov>

http://www.spacedaily.com/news/lunarplanet-2001-01a8.html

Rocks From Mars
by Bruce Moomaw
SpaceDaily

Cameron Park - June 1, 2001
Finally, the debate continued to rage on at the Conference as to whether the
famous Martian meteorite ALH84001 does or does not contain meaningful fossil
evidence of ancient Martian microbes.

Indeed, this rock is starting to look as Sphinx-like to scientists as the
entire planet currently does.

Kathie Thomas-Keprta and her team at the Johnson Space Center -- who set off
a sensation in 1996 by announcing the supposed evidence in the first place
-- reiterated their belief that some of the microscopic magnetite crystals
within the tiny carbonate granules found within the rock are shaped such
unusual "elongated hexa-octahedral" forms, and so uniform in size, that
there is almost certainly no nonliving process that could have crated them
-- and that they therefore must have been created by ancient Martian
"magnetotactic" bacteria that evolved to take advantage of Mars' now-dead
magnetic field by using such crystals inside their cells to point themselves
like compass needles in the right direction to take maximum advantage of
some kinds of nutrients in underwater sediment, as some Earth bacteria have
done.

Allan H. Treiman countered by saying that "each characteristic of [these
crystals] is consistent with an abiotic origin", and that they could easily
have been formed by the rapid heating of iron carbonate in the carbonate
granules by volcanic heat, or even by the heat of the giant meteor impact
that launched the meteorite off Mars' surface and onto its long voyage to
Earth.

Imre Friedmann, however, countered Treiman by repeating his argument --
recently detailed in "Science" -- that some of these unusual magnetite
crystals are laid out in chain-like formations that simply could not have
been created by any such nonliving crystallization process -- indeed, that
they look as though they were originally separated at even distances from
each other by now-vanished organic material.

While no paper at the LPSC countered this argument, though, it has been
reported elsewhere that the visual microscopic evidence of such chains is
actually far more ambiguous than Friedmann and his supporters make it out to
be.

And one thing that has become clear is that these magnetite crystal chains
are pretty much the "last stand" where possible fossil evidence of life in
ALH84001 is concerned -- every other apparent piece of evidence can now be
convincingly explained as having perhaps been made in other ways by
nonliving processes.

Robert Folk, who has been playing the scientific maverick for some years by
claiming widespread microscopic evidence of super-tiny "nanobacteria", said
that his new studies of this and another Martian meteorite showed that tiny
nanometer-scale mineral ovoids similar to the possible "bacterial fossils"
reported inside AL:H84001 also exist in very large numbers on the outside
surfaces of both meteorites -- indicating that these ovoids, whether they're
produced by nonliving processes or living "nanobacteria", were very likely
deposited on and inside the meteorites AFTER their arrival on Earth and
therefore do not constitute evidence of Martian microbes.

And J.P. Greenwood and J. Farquhar reported that, while peculiar ratios of
sulfur trace isotopes often serve as a sign in Earthly environments that
living microbes have been metabolizing nutrients there in the past -- there
are no clear signs of such isotopic anomalies within the minerals of
ALH84001 and two other Mars meteorites studied.

Farquhar reiterated his recent report in "Nature" that there's a good chance
that simple solar UV light striking Martian minerals can also produce such
sulfur isotoic "fractionation" effects, making it doubtful that sulfur
isotopes can ever be used by themselves as any meaningful evidence of
Martian life.

Finally, two researchers suggested longer-shot evidence that the surface of
present-day Mars -- despite its seemingly savage environment -- may even
contain large amounts of alive and thriving microbes.

D.M. Warmflash suggested that the discovery of traces of organic compounds
within the Mars meteorites may mean that the Viking landers were wrong in
indicating a total absence of organic compounds in Mars' surface soil --
and, therefore, that the puzzling results from the landers' "Labeled
Release" tests for living microbes, which are still rather hard to explain
by means of the hypothesized organic-destroying "soil oxidants", may really
have detected living and growing germs., as its designer Gilbert Levin still
insists.

And Hungarian scientist A. Horvath made an even bolder proposal regarding
the remarkable dark spots that MGS has discovered appearing in great numbers
on the tops of Martian polar-region dunes in spring and expanding as the
season progresses.

Michael Malin and Ken Edgett think this is simply due to the fact that
sunlight hitting the tops of the dunes thaws the frosts of CO2 and/or water
off them first, and then that this darker frost-free soil is heated by the
sunlight and in turn heats the soil around it to rapidly expand the thawed
area.

Horvath, however, thinks the dark spots may actually be large films of
living Martian algae taking advantage of water frost melting on the dunes in
spring to rapidly grow and reproduce before retreating back into dormant
spore form after the liquid film of water disappears.

His main piece of evidence for this is that the dark spots tend to elongate
and form long streaks running down the surfaces of dunes, indicating that
they are associated with the actual presence of liquid water on the dune
surfaces.

But there are possible alternative explanations for this -- for instance,
E.F. Albin reported similar dark streaks running down frost-free Martian
slopes elsewhere, which may be due to local releases of subsurface carbon
dioxide which have formed miniature versions of Nick Hoffmann's
"cryoclastic" eruptions and swept material downslope to blow away lighter
fine surface dust.

It may be that Malin and Edgett's theory just needs to be mildly modified --
that frozen CO2 or water vaporizing out of the upper centimeters of dune
material in the dark spots tends to flow downslope and either heat up and
evaporate the frost down there, or sweep away lighter-colored fine dust on
the dune surfaces to expose the darker coarse dust underneath.

(It is certainly known that frozen CO2 thawing out of the soil around the
south polar cap in spring kicks enough dust into the air to absorb sunlight,
further warm the surrounding air, and so create Mars' self-amplifying dust
storms.) And MGS has also found the tops of the polar dunes are also the
very first spots to refrost in fall, further indicating that all of this is
just a nonliving weather process.

In short, the major conclusion one is forced to from this year's LPSC papers
on Mars is that -- while we are teetering on the very brink of a general
understanding of the planet's geological and climate history -- we still
haven't crossed that brink.

Indeed, the new "White Mars" theory that most of what we thought was caused
by liquid water on Mars' surface is really due to carbon dioxide has
actually further complicated the picture in the past two years.

We still need more data to solve the problem.

MGS will continue to photograph more and more small spots on the planet with
2-meter resolution; and the Mars Odyssey craft now on its way to orbit Mars
should certainly provide us with more useful evidence with its THEMIS
infrared camera (which can try to map carbonates and other surface minerals
with a resolution of only 100 meters, search for local spots of still-active
geothermal warmth, and photograph much of the planet with 30-meter
resolution) and its gamma-ray spectrometer (which should give us our first
overall global map of the distribution of important elements in Mars'
surface rocks, and can also detect both water ice and frozen CO2 at depths
down to 30 cm below the soil surface) -- but it seems unlikely that these
two instruments by themselves can crack the puzzle.

We are much more likely to make that final breakthrough in understanding the
nonliving processes on Mars from the spacecraft set to travel to Mars in
2003 -- the two American "MER" rovers, Europe's "Mars Express" orbiter with
its large set of new and important instruments for surface mapping
(especially its subsurface radar sounder), and the little Beagle 2 lander
that it will carry.

And only after we have that understanding of nonliving Mars will we be in a
really good position to estimate the chances that early Mars did evolve life
-- and even that present-day Mars may conceivably still bear it in preserved
shelters under the planet's surface.
Received on Mon 04 Jun 2001 12:29:16 PM PDT