Mars Astrobiology: Recent Status and Progress - Planetary Exploration and Science: Recent Results and Advances - page 150

Even the most radiation-tolerant Earthly bacteria would survive in dormant spore
state only 18,000 years at the surface; at 2 m - the greatest depth at which the
ExoMars rover will be capable of reaching - survival time would be 90,000 to half
million years, depending on the type of rock.
The Radiation Assessment Detector (RAD) on board the Curiosity rover is
currently quantifying the flux of biologically hazardous radiation at the surface of
Mars today and will help determine how these fluxes vary on diurnal, seasonal,
solar cycle, and episodic (flare, storm) timescales. These measurements will allow
calculations of the depth in rock or soil to which this flux, when integrated over long
timescales, provides a lethal dose for known terrestrial organisms.
Research published in January 2014 of data collected by the RAD instrument
revealed that the actual absorbed dose measured is 76 mGy/year at the surface and
that ionizing radiation strongly influences chemical compositions and structures,
especially for water, salts, and redox-sensitive components such as organic matter
(Hassler and MSL Science Team 2014 ).
Regardless of the source of Martian organic matter (meteoritic, geological, or
biological), its carbon bonds are susceptible to breaking and reconfiguration with
the surrounding elements by ionizing charged particle radiation. These improved
subsurface radiation estimates give insight into the potential for the preservation
of possible organic biosignatures as a function of depth as well as survival times
of possible microbial or bacterial life forms left dormant beneath the surface. The
report concludes that the in situ surface measurements - and subsurface estimates -
constrain the preservation window for Martian organic matter following exhumation
and exposure to ionizing radiation in the top few meters of the Martian surface
(Hassler and MSL Science Team 2014 ).

8.2.2.4 Nitrogen Fixation

After carbon, nitrogen is arguably the most important element needed for life.
Thus, measurements of nitrate over the range of 0.1-5 % are required to address
the question of its occurrence and distribution. There is nitrogen (as N 2 )inthe
atmosphere at low levels, but this is not adequate to support nitrogen fixation for
biological incorporation. Nitrogen in the form of nitrate, if present, could be a
resource for human exploration both as a nutrient for plant growth and for use
in chemical processes. On Earth, nitrates correlate with perchlorates in desert
environments, and this may also be true on Mars. Nitrate is expected to be stable
on Mars and to have formed in shock and electrical processes. Currently, there is no
data on its availability.

8.2.2.5 Low Pressure

Further complicating the estimates of the habitability of the Martian surface is the
fact that very little is known on the growth of microorganisms at pressures close