[meteorite-list] A Case for Life on Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:24 2004
Message-ID: <200209121902.MAA27031_at_zagami.jpl.nasa.gov>

http://www.spacedaily.com/news/mars-life-02f.html

A Case for Life on Mars
SpaceDaily
September 12, 2002

Leicester - A multitude of arguments supporting the possible
existence of life on Mars have surfaced after the discovery
and examination of the ALH84001 meteorite. The polycyclic aromatic
hydrocarbons (PAHs) found within, plus detailed examination of
the ratios of certain metabolites, all have various
interpretations supporting or opposing their organic origin.

In a recent NASA workshop, the results of careful
sectioning, imaging, identification of mineral constituents,
measurement of isotope ratios and analysis of the organic matter in
the meteorite were compared. In the process of filtering out the
evidence supporting microbes, new avenues of investigation are
being conceived, leading to the current flourishing of exobiological
methodology.

The geological record of Mars suggests that its environment was
similar to the Earth's prior to about 3.5 billion years (Gyr) ago,
when terrestrial life was first emerging. In particular, there is
abundant evidence for liquid water, in the form of rivers, lakes and
possibly even larger bodies of water, on the Martian surface at
that time.

CO2 clouds can regulate the Martian climate by re-scattering
infrared (IR) radiation, effectively warming the planet to habitable
temperatures. As liquid water is thought to be essential for biology,
the environment on early Mars may well have been favourable for
the development of life.

Although some remain sceptical, the knowledge to date validates a
concise effort to search for evidence of either past life or presently
existing life. Recent research has revealed that there is active
biota on Earth living in environments once thought impossible.

Underwater vents, where the pressure approaches 100 atm and
the temperature is 80-120 oC, provide everything necessary for
organisms to live and flourish. Even more astonishing is the fact
that a species of mite called tardigrades, less than half a millimetre
long has been found to be able to survive boiling, freezing and
exposure to a vacuum.

The results show that these microscopic animals, can withstand
pressures of up to 6000 atmospheres by entering a state of
suspended animation, which can be maintained for more than a
century.

To accomplish this they reduce their body weight by 50% or more,
accompanied by an almost total loss of water using a sugar called
trehalose to stabilise their cell membranes. Such evidence points
towards a re-evaluation of our current beliefs on how essential
liquid water is to the development and preservation of life.

Examination of terrestrial biota reveals that life-forms have invaded
an enormous variety of 'non-optimum' niches, for example cold
polar regions and desert belts, where the essential ingredients for
life are rare.

The simple conclusion therefore is that one of life's most
conspicuous properties is its aggressive versatility, which arises
from its fundamental ability to create new experimental organisms
during evolution. Life on modern Mars would admittedly be very
challenging, the largest obstacle being the lack of ample liquid
water which would hinder metabolism, mobility and reproduction.

All other obstacles though, like UV, ionising radiation and lack of
organic compounds are all routinely accommodated through
numerous strategies adopted by terrestrial organisms. Similar
strategies may have been developed by organisms on Mars and
could have manipulated the natural resources to the same effect.

The notion that photosynthetic organisms would not be able to
survive on the surface due to UV radiation should be reconsidered
after considering that the natural environment on Mars could be
used to attenuate UV radiation with only minor attenuation of
visible light.

A number of natural absorbers are readily available on the planet,
such as nitrate, nitrite and sulphate salts. Fe-containing silica
glass can be used as a cuticle protecting cell contents.
Furthermore, the ferric iron (Fe203) in the environment may have
protected phototrophs in ancient microbial mats in shallow aquatic
environments.

Recent in-situ analysis has demonstrated regolith chemical
constituents that allow the above cases to manifest themselves on
Mars. Volcanic sources in conjunction with gases produced by the
action of UV photons on the atmosphere, would allow
chemolithoautotrophic life forms to exploit solar energy without the
need for direct capture of photons.

The combination of an appropriate energy source with an effective
UV shielding mechanism thus demonstrates how an organism can
take advantage of a multitude of niches existing in its environment.

In addition, there is growing evidence that cross-contamination
between Earth and Mars may have occurred, leading to the
possible conclusion of a single origin of life in the solar system, the
panspermia theory. This hypothesis alone forms a realistic scenario
supporting the case for life on Mars.

Certainly new evidence is demonstrating to us that life has a
profound ability to adapt to extreme and variable conditions and it
is entirely plausible that if life once existed on Mars, it may have
found a niche and indeed still exists.
Received on Thu 12 Sep 2002 03:02:28 PM PDT