Sara Seager and I are working on potential biosignatures that could be detected in the atmospheres of exoplanets. Sara is a Professor of physics at MIT, and one of the leading thinkers about exoplanets and their atmospheres. See here for Sara's web pages.
Astronomers are discovering new planets around other stars at a rate of about 1/day. But we cannot land spacecraft on them. The fastest manmade machine ever – the Helios 2 spacecraft – would take 17,000 years to get to the nearest star at its top speed. So we have to analyse them remotely by spectroscopy to see if their chemical composition has been altered significantly by life on their surface and in their oceans. This means their atmospheric composition, which can be detected (in principle) from the spectrum of light emitted, reflected and absorbed by their atmosphere.
Life has radically altered the atmosphere of Earth, filling it with oxygen. However early Earth had life but very little oxygen, so other ‘biosignature’ gases might also be signs of life. Different planets with different rock chemistry, volcanism, temperature or atmospheric masses could also show different biosignatures. This project seeks to catalogue what worlds might be possible and how life would transform their atmospheres, so when we build telescopes sensitive enough to find these worlds, we have a head start on deciding how to look for signs of life.
The most recent model we have been building is SulfurWorld (no, I will not call it Vulcan), a world dominated by volcanoes where the air is thick with sulfur dioxide and a haze of acids and sulfur flakes hangs 30km in the sky. See Can Hydrogen Sulfide Gas Be a Biosignature in a Habitable Exoplanet? for an initial summary of this work.