Examining the Ability of Sulfur-Bearing Gases to act as Biosignatures on Anoxic Planets

Details Examining the Ability of Sulfur-Bearing Gases to act as Biosignatures on Anoxic Planets Examining the Ability of Sulfur-Bearing Gases to act as Biosignatures on Anoxic Planets

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p33d..07d&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P33D-07

Biology

0312 Air/Sea Constituent Fluxes (3339, 4504), 0406 Astrobiology And Extraterrestrial Materials, 0426 Biosphere/Atmosphere Interactions (0315), 5210 Planetary Atmospheres, Clouds, And Hazes (0343), 5225 Early Environment Of Earth

Scientific paper

The search for life on extrasolar planets will depend on our ability to detect the presence of biogenic gases in the atmospheres of those planets using spectroscopy. For example, the presence of life on a planet similar to modern-day Earth could be detected by the simultaneous presence of molecular oxygen and methane in the planet's atmosphere, as indicated by their spectral features. However, for a significant portion of life's history on Earth no molecular oxygen was present in the atmosphere. Thus, the detection of a biosphere similar to the one that existed on Earth before the rise of atmospheric oxygen requires the study of novel biosignatures. Biogenic S-bearing gases may be able to act as biosignatures on such a planet. The two main sinks for these gases in the modern atmosphere are oxidation and photolysis, and they may build up to higher concentrations in atmospheres that have lower UV fluxes and a less oxidizing chemistry. These conditions may have been present on the early Earth, when the lack of molecular oxygen should have decreased the oxidation rate of these gases and an organic haze could have shielded them from photolysis. In this presentation, we will present the results of a 1-D photochemical model of the early Earth that includes the biogenic gases dimethyl disulfide (CH3-S-S-CH3), dimethyl sulfide (CH3-S-CH3), methyl mercaptan (CH3SH), carbon disulfide (CS2), and carbonyl sulfide (OCS). Specifically, we predict the mixing ratios and spectral features that could result when these gases are released into an anoxic atmosphere similar to the one thought to have existed on the early Earth. We also consider the potential for abiogenic sources of these species to create false positives for biology. The discussion will focus on the effects of atmospheric oxidation state and UV flux on the abundance of these gases and their corresponding ability to act as remotely detectable biosignatures.

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