On this Student Spotlight: Have we been looking for aliens using the wrong parameters?
Joshua Krissansen-Totton, graduate student in the department of earth and space sciences at the University of Washington, explains why searching for just oxygen among the cosmos might not lead us to E.T.
Department of Earth and Space Sciences
Virtual Planetary Laboratory
University of Washington
Searching for Life in Space using Methane
For the first time in human history, technology has matured to the point where it is possible to look for life on planets around other stars. Large telescopes will soon observe the atmospheres of distant worlds to look for telltale biological waste gases.
Up until now, the most promising waste gas has been oxygen. Virtually all the oxygen in Earth’s atmosphere was made by photosynthesis; indeed, it is difficult to make oxygen without life.
However, even if life is common in the cosmos, there’s no guarantee that oxygen rich atmospheres are also common. The biochemistry required for oxygen production is incredibly complex and only evolved once on Earth. Therefore, it makes sense to develop alternative approaches to looking for life.
In our study, we examined the gases in Earth’s atmosphere over its long history and looked for new, potential biological combinations. We found that in the first two billion years, Earth’s atmosphere was ‘out of equilibrium’, because both carbon dioxide and methane were present, and chemistry predicts these two gases should not coexist without a continuous resupply of methane. On the Ancient Earth this methane was supplied by life. Non-biological processes cannot easily generate massive amounts of methane, therefore we argued that detecting these two gases on another world would be a sign of life.
Methane-rich biospheres are almost certainly more common than oxygen-rich biospheres because unlike photosynthesis, the biochemistry of methane-production is simple and ubiquitous. And most importantly, methane and carbon dioxide are detectable. After launching in 2019, NASA’s James Webb Space Telescope will peer into the atmospheres of nearby, habitable planets, and could potentially detect methane and carbon dioxide. Thus, the new ‘biosignature’ that we propose could soon be the first sign of life beyond Earth.