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August 28th, 2021
Credit: NASA
On Mars, pit craters and cave skylights would be effectively shielded from the damaging ultraviolet radiation (UV) on the Martian surface. Furthermore, the attenuated UV irradiance in cavernous spaces remains stable at least in a 10 million year timescale.
Additionally, the radiation environment offered by voids on the Red Planet may represent favorable environments for habitability.
Those are a few takeaway messages from new research by D. Viúdez-Moreiras at the Centro de Astrobiología (CSIC-INTA) & National Institute for Aerospace Technology (INTA) in Madrid, Spain.
Preserved evidence of life
“Caves and their entrances have been proposed as habitable environments and regions that could have preserved evidence of life, mostly due to their natural shielding from the damaging ionizing and non-ionizing radiation present on the surface. However, no studies to date have quantitatively determined the shielding offered by these voids on Mars,” explains Viúdez-Moreiras.
The just-published paper presents for the first time the UV radiation environment in typical void geometries found to date on Mars.
Illustrative void captured by the Mars Reconnaissance Orbiter’s HiRISE camera northeast of Arsia Mons on the Red Planet. Cavernous spaces are expected in many of these voids.
Credit: MRO/HiRISE/University of Arizona
“The intermediate radiation environment between the damaging radiation on the surface and the permanent darkness of a hypothetical cave offered by voids on Mars may represent favorable environments for habitability without constraining the type of energy source for potential as-yet unknown Martian organisms,” Viúdez-Moreiras reports.
Surface hazards
The researcher notes that the thin Martian atmosphere offers poor protection against ionizing and UV radiation, and, together with the lack of a planetary-scale magnetic field to filter ionizing radiation, allows high levels of radiation to reach the Martian surface.
“The radiation levels on Mars represent an additional difficulty for the survival of life on the surface, at least based on the present knowledge, in addition to the degradation of possible organic molecules produced by biogenetic or abiotic processes,” Viúdez-Moreiras points out.
The subsurface of Mars would not only be shielded from radiation fluxes, but also offer protection against small-scale meteorite impacts wind processes and extreme weather such as the dust storms that typically impact the Martian surface.
Location of candidate caves in the Tharsis region on Mars.
Credit: USGS
Small features
However, Viúdez-Moreiras flags the fact there are difficulties in detecting these small features in the Mars topography, preventing a wide number of pit craters and cave entrances being discovered to date.
Possible cave entrances based on skylights on Mars have been observed from orbit by NASA’s Mars Odyssey Thermal Emission Imaging System (THEMIS) in the Tharsis region. Also, imagery analyzed from NASA’s Mars Reconnaissance Orbiter (MRO), Mars Odyssey and Mars Global Surveyor of Elysium Mons has resulted in the detection of thirty-two skylight candidates.
Viúdez-Moreiras concludes that pit craters and cave skylights “present strong interest from an astrobiological perspective in terms of potential habitability and regions that could have preserved evidence of life, given the protection these environments offer against the hazards on the surface of Mars, such as UV radiation.”
Mars expedition probes the promise that Mars was a home address for past, possibly life today.
Credit: NASA
Needed: More data, modeling work
“Pit craters and cave skylights, which are intermediate in terms of UV radiation between the damaging levels present on the Martian surface and the permanent darkness of a hypothetical cave, may offer environments favorable for the habitability and preservation of organic molecules in locations that would be relatively easy to access by surface missions.”
Viúdez-Moreiras suggests that further modeling work and more data from current and future missions would be necessary to appraise the habitability of these environments.
To read the full paper in the journal Icarus – “The ultraviolet radiation environment and shielding in pit craters and cave skylights on Mars” – go to:
https://www.sciencedirect.com/science/article/pii/S0019103521003171
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