Quantifying the potential biosphere of Mars

Terrestrial life is known to require liquid water, but not all terrestrial water is inhabited. Thus, liquid water is a necessary, but not sufficient, condition for life. In this project, we have worked on developing and comparing empirical pressure-temperature (P-T) phase diagrams of water, Earth, and terrestrial life, to quantify the terrestrial limits on the habitability of water and help identify the factors that cause some terrestrial water to be uninhabited. 

Eighty-eight percent of the volume of Earth where liquid water exists is not known to host life. This potentially uninhabited terrestrial liquid water includes: i) hot and deep regions of Earth where some combination of high temperature (T > 122˚C) and restrictions on pore space, nutrients, and energy is the limiting factor, and ii) cold and near surface regions of Earth, such as brine inclusions and thin films in ice and permafrost (depths less than ~1 km), where low temperatures (T < -40˚C), low water activity (aw < 0.6), or both are the limiting factors. If the known limits of terrestrial life do not change significantly, these limits represent important constraints on our biosphere and, potentially, on others, since ~4 billion years of evolution have not allowed life to adapt to a large fraction of the volume of Earth where liquid water exists.

We are also working on a pressure-temperature (P-T) phase model for Mars to identify environments on Mars that may have liquid water and be able to support terrestrial-like life. Using the phase model we estimate the depths on Mars where P and T conditions match those of environments hospitable to life on Earth. To further determine whether these environments are hospitable to terrestrial life we estimate the availability and activity of liquid water in these environments on Mars. We will then conduct subsurface temperature modelling using remotely sensed data and ArcGIS to identify potential locations and depths of shallow liquid water on present-day Mars.

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