HYDROTHERMAL SYSTEMS AND THE SEARCH FOR EXTRATERRESTRIAL LIFE

Hydrothermal systems develop where a fluid phase coexists with a heat source. They link global lithospheric, hydrologic and atmospheric cycles and over geologic time, contribute to the evolution of oceans and atmospheres. Hydrothermal systems have been implicated in the abiotic synthesis of organic compounds required by life. They may have also sustained life’s origin and are likely to have provided refuges for the biosphere during late giant impact events that overlapped with early biosphere evolution. Because subsurface fluids and crustal heat sources are likely to have been widespread on other planetary bodies in the Solar System, hydrothermal systems and their deposits, are regarded as important targets for exopaleontology (1,2).

Hydrothermal systems probably played an important role in the early history of the dark asteroids, which are considered the most likely parent bodies for the C-1 (carbonaceous) chondrites. These meteorites, which show evidence for extensive aqueous alteration over a temperature range of 50 - 100 °C, were an important source of exogenous prebiotic organics on the early Earth. Given the potential for abundant water, sustained heat sources, and reduced compounds, hydrothermal systems on Europa could have provided long-term habitats for chemotrophic microbial ecosystems, similar to those found in deep sea vent environments on Earth. Hydrothermal environments were probably also widespread on Mars early in the planet's history. Their deposits have been cited as important targets in the search for a Martian fossil record. Small channel networks located on steep, poleward-facing slopes at high latitudes on Mars, may have been formed by recent outflows of near surface hydrothermal brines, thus providing potentially habitable environments for a subsurface biosphere on Mars today.

(1) Farmer, Jack D. 2000. Hydrothermal Systems: Doorways to Early Biosphere Evolution, GSA Today 10(7), 1-9.

(2) Farmer, J.D. 2000, Exploring for a fossil record of extraterrestrial life, p. 10-15 In Derek Briggs and P. Crowther (eds.) Palaeobiology II, Blackwell Science Publishers, Oxford.