As we look for biosignatures on other planets, we should guard against being too Earth-centric.
Many of the space missions we send to Mars and other planets search for evidence of life. Or rather, they search for life as we know it — life that’s made of carbon, requires liquid water, and uses light or chemical energy as its main energy source. Sara Seager and her colleagues from MIT, William Bains and Renyu Hu, want to expand this “earth-centric” approach. They suggest looking for any gas that is out of equilibrium as a possible signature of life on exoplanets. (We say “possible” because geological processes, particularly volcanic eruptions, can also affect the equilibrium.)
On Earth, the out-of-equilibrium gases oxygen and methane are a biosignature. If they were not constantly replenished by life processes (plants that produce oxygen and bacteria that produce methane) the two gases would react to produce the relative inert gas carbon dioxide.
Seager and her colleagues built a model that predicts how elements might combine naturally in the atmospheres of other planets. By comparing the model to actual observations of exoplanet atmospheres, the presence of life might be revealed. For example, for planets with atmospheres dominated by ...