Geoscience Reference
In-Depth Information
Habitability factors
Wat er
Liquid water activity (a
w
)
Past/future liquid (ice) inventories
Salinity, pH, and Eh of available water
Chemical environment
Nutrients
C, H, N, O, P, S, essential metals, essential micronutrients
Fixed nitrogen
Availability/mineralogy
Toxin abundances and lethality
Heavy metals (e.g., Zn, Ni, Cu, Cr, As, Cd, etc., some
essential but toxic at high levels)
Globally distributed oxidizing soils
Energy for metabolism
Solar
(surface and near-surface only)
Geochemical
(subsurface)
Oxidants
Reductants
Redox gradients
Conducive physical conditions
Temperature
Extreme diurnal temperature fluctuations
Low pressure (is there a low-pressure threshold for terrestrial
anaerobes?)
Strong ultraviolet germicidal irradiation
Galactic cosmic radiation and solar particle events (long-term
accumulated effects)
Solar UV-induced volatile oxidants, e.g., O
2
,O
,H
2
O
2
,O
3
Climate/variability (geography, seasons, diurnal, and
eventually obliquity variations)
Substrate (soil processes, rock microenvironments, dust
composition, shielding)
High CO
2
concentrations in the global atmosphere
8.2.2.1
Subsurface
Although Mars soils are likely not to be overtly toxic to terrestrial microorganisms,
life on the surface of Mars is extremely unlikely because it is bathed in radiation
and it is completely frozen. But extremophiles could hypothetically be able to
thrive through such harsh conditions. Therefore, the best potential locations for
discovering life on Mars may be at subsurface environments that have not been
studied yet. The extensive volcanism in the past possibly created subsurface cracks
and caves within different strata where liquid water could have been stored, forming
large aquifers with deposits of saline liquid water, minerals, organic molecules,
and geothermal heat - potentially providing a habitable environment away from
the harsh surface conditions.
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