Was Early Mars a Habitat for Life?

Mars Basic Data

Mean Radius = 3389.9 km                  Semi-major Axis = 1.524 AU
Mass = 6.4185E23 kg                      Equatorial Gravity = 3.690 m/s2
Sidereal Rotation Period = 24.622962 hr  Atmospheric Pressure = 0.0056 bar
Moment of Inertia = 0.366                Mean Temperature = 210 K
Radius of Core = about 1700 km           Geometric Albedo = 0.150
Density = 3.933 g/cc                     Sidereal Orbital Period = 1.88081578 yr
Flattening = 1/154.409                   Escape Velocity = 5.027 km/s
Obliquity to Orbit = 25.19 deg           Orbit Inclination = 1.850 deg
Orbit Eccentricity = 0.0935              Length of Day = 24.6597 hr
Number of Natural Satellites = 2 (Phobos and Deimos)

Atmospheric Composition
Surface Pressure: about 6.1 mb (variable)
Diurnal Temperature Range: 184 K to 242 K (Viking 1 Lander site)
Mean Molecular Weight: 43.34 g/mole
Major Species (vol): CO2 - 95.32%; N2 - 2.7%
                     Ar - 1.6%; O2 - 0.13%; CO - 0.08%
Minor Species (ppm): H2O - 210; NO - 100; Ne - 2.5;
                     HDO - 0.85; Kr - 0.3; Xe - 0.08

Searching for Life on Mars means Following the Water

Since life as we know it is based on water, determining the best sites to search for any life that may have once existed on Mars means finding sites where ancient rivers, lakes and seas may have existed. Shown in the image below is an exhumed sedimentary distributary fan. Distributary fans include river deltas and alluvial fans. Sometime in the past when the climate of Mars may have allowed liquid water to flow across the surface of the planet, sediments transported through valleys by water formed a fan-shaped deposit in a 64 kilometer diameter crater northeast of Holden Crater. The landform described above may be the strongest indicator that some craters (such as Gusev - the MER-B landing site) and other depressions on Mars once held lakes.

Evidence of Possible Microbial Life in the Mars Meteorite ALH84001

ALH84001 is a coarse-grained orthopyroxene meteorite containing relatively large amounts of carbonate, with a crystallization age of about 4.5 billion years. Carbonate globules found within fractures in the rock are dates at about 3.6 billion years.

ALH84001 is just one of 12 known SNC meteorites which are thought to orginate from Mars. The graph below presents isotopic ratio evidence for meteorite EETA79001 in favor of the Mars origin scenario.

ALH84001 contains approximately 1 ppm PAHs (Polycyclic Aromatic Hydrocarbons), found on fracture surfaces inside the meteorite. PAHs are large, complex organic molecules that are abundant in interplanetary dust particles, interstellar dust, and many organic-rich meteorites from the asteroid belt. However, the PAHs found in ALH84001 are thought to originate from the breakdown products of organisms that once lived in the ancient rock. This scenario assumes that the PAHs found in the martian meteorite are not the result of terrestrial contaminants produced by power plants and automobile exhaust. However, the data for ALH84001 (shown below) indicates that the PAHs are concentrated towards the interior of the rock which implies that terrestrial contamination in not likely.

High resolution scanning electron microscope images show what appear to be "ovoids" that may be microfossils from Mars. However, it is important to note that, at 20 to 100 nanometers in dimension, these objects are about 100 times smaller than the smallest ancient bacterial fossils found on Earth.

Future studies on a genetic level to look for cell walls and amino acids in individual "ovoids" are in the planning phase. Any such "ovoids" caught in the act of dividing would support the theory that primative bacteria have been found in ALH84001.

Evidence for Microbial Life in Martian Meteorite Nakhla

Nakhla is a member of the Nakhlite group of achondrites and is composed mosly of clinopyroxene with minor amounts of feldspar, sulfides and oxides. Nakhla has a crystallization age of 1.3 Gyr and contains clay- filled cracks of Martian origin. Light microscope images reveal rounded micrometer sized structures embedded within the clay-filled cracks. On closer examination using SEM, these features consist of 0.5-2 micron-sized spheres with irregular surfaces. They occur in distinct cluster-like distributions within the clay (see images below). These spheres and ovoids in the Nakhla meteorite are simular to the fossils of terrestrial coccoid bacteria. However, it is important to emphasize that spherical and/or ovoid morphology alone are not indicative of biogenic activity.

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