Geoscience Reference
In-Depth Information
Observations on Earth and numerical modeling have shown that a crater-forming
impact can result in the creation of a long-lasting hydrothermal system when ice
is present in the crust. For example, a 130-km large crater could sustain an active
hydrothermal system for up to 2 Ma, that is, long enough for microscopic life to
emerge (Westall et al.
2013
).
Soil and rock samples studied in 2013 by NASA's Curiosity rover's on board
instruments brought about additional information on several habitability factors.
The rover team identified some of the key chemical ingredients for life in this soil,
including sulfur, nitrogen, hydrogen, oxygen, phosphorus and possibly carbon, as
well as clay minerals, suggesting a long-ago aqueous environment - perhaps a lake
or an ancient streambed - that was neutral and not too salty. On December 9, 2013,
NASA reported that, based on evidence from Curiosity studying Aeolis Palus, Gale
Crater contained an ancient freshwater lake which could have been a hospitable
environment for microbial life.
The confirmation that liquid water once flowed on Mars, of the existence of
nutrients, and of the previous discovery of a past magnetic field that protected the
planet from cosmic and solar radiation together strongly suggests that Mars could
have had the environmental factors to support life. However, the assessment of past
habitability is not in itself evidence that Martian life has ever actually existed. If
it did, it was probably microbial, existing communally in fluids or on sediments,
either free-living or as biofilms, respectively (Dehant et al.
2007
; Summons et al.
2011
; Various
2014
).
8.2.2
Present Mars
No definitive evidence for biosignatures or organics of Martian origin has been
identified, and assessment will continue not only through the Martian seasons but
also back in time as the Curiosity rover studies what is recorded in the depositional
history of the rocks in Gale Crater. While scientists have not identified the minimum
number of parameters for the determination of habitability potential, some teams
have proposed hypotheses based on simulations.
Scientists do not know the minimum number of parameters for the determination
of habitability potential, but they are certain it is greater than one or two of the
factors in the table below. Similarly, for each group of parameters, the habitability
threshold for each is to be determined. Laboratory simulations show that whenever
multiple lethal factors are combined, the survival rates plummet quickly. There
are no full-Mars simulations published yet that include all of the biocide factors
combined.
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