Abstract
The low temperatures and high ultraviolet (UV) radiation levels at the surface of Mars today currently preclude the survival of life anywhere except perhaps in limited subsurface niches. Several ideas for making the martian surface more habitable have been put forward previously, but they all involve massive environmental modification that will be well beyond human capability for the foreseeable future. Here we present a new approach to this problem. We show that widespread regions of the surface of Mars could be made habitable to photosynthetic life in the future via a solid-state analogue to Earth's atmospheric greenhouse effect. Specifically, we demonstrate via experiments and modelling that under martian environmental conditions, a 2 to 3-cm thick layer of silica (SiO2) aerogel will simultaneously transmit sufficient visible light for photosynthesis, block hazardous ultraviolet radiation, and raise temperatures underneath permanently to above the melting point of water, without the need for any internal heat source. Placing silica aerogel shields over sufficiently ice-rich regions of the martian surface could therefore allow photosynthetic life to survive there with minimal subsequent intervention. This regional approach to making Mars habitable is much more achievable than global atmospheric modification. In addition, it can be developed systematically starting from minimal resources, and can be further tested in extreme environments on Earth today.
Highlights
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We show that widespread regions of the surface of Mars could be made habitable to photosynthetic life in the future via a solid-state analogue to Earth’s atmospheric greenhouse effect
Observations of dark spots on Mars’ polar CO2 ice caps suggest that they are transiently warmed by a greater amount via a planetary phenomenon known as the solid-state greenhouse effect [10, 11, 12, 13], which arises when sunlight becomes absorbed in the interior of translucent snow or ice layers [14, 15]
Summary
Our experimental setup consisted of an 18 cm × 18 cm solid-state greenhouse layer of variable thickness surrounded by polystyrene for insulation, with a solar simulator positioned above the layer to provide varying levels of visible irradiance. The optical properties of silica aerogel do not vary significantly across the visible wavelength range [36], so the relatively small differences between the metal-halide lamp spectrum and the solar spectrum incident at Mars’ surface were not a significant source of uncertainty in our results either. All experiments were run until thermal equilibrium was reached, which was judged by observing the value and rate of change of temperature at the base and top of the silica aerogel layer. This took around two hours for each experiment. The UV-A/B detector had peak sensitivity in the 350-360 nm range, with the calibration point at 365 nm, while the UV-C detector had peak sensitivity at 255-265 nm, with the calibration point at 254 nm
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