Windows into Deep Subsurface Chemistry Near and Far (Invited)

Earth's deep biosphere may be just one of many deep biospheres within our solar system. But for many of these worlds we are, and will be for the near future, limited to observations and measurements of the surface chemistry to serve as a window into any activity related to geochemical or biochemical disequilibrium. Mars, Europa, and Enceladus serve as three examples of worlds where the surface of the lithospheres (one silicate, the other two of water ice) may connect to rich subsurface aqueous chemical environments. Here I will present results from recent observations of the surface chemistry of Europa and the organic- and salt-rich plume material of Enceladus. Interestingly, for at least the case of Europa, the redox chemistry of the deep lithosphere may be inverted when compared to that of the Earth. On Earth, the rocks of the lithosphere serve as the reductant and the fluid and dissolved gases provide the oxidants. On Europa, the rock of its lithosphere is water ice that is likely permeated with oxygen, peroxides, and sulfate compounds. The lithosphere may be reductant limited. Coupled with these observations I will also present recent results from work on Arctic methane seeps and Hadal zone observations of biological and geochemical processes. These environments provide a unique window into the deep biosphere and illuminate some of the challenges of differentiating biochemical products from geochemical products.