This artist’s illustration shows two Earth-sized planets, TRAPPIST-1b and TRAPPIST-1c, passing in front of their parent red dwarf star, which is much smaller and cooler than our sun. NASA’s Hubble Space Telescope looked for signs of atmospheres around these planets. (NASA/ESA/STScI/J. de Wit, MIT)
What observations, or groups of observations, would tell exoplanet scientists that life might be present on a particular distant planet?
The most often discussed biosignature is oxygen, the product of life on Earth. But while oxygen remains central to the search for biosignatures afar, there are some serious problems with relying on that molecule.
It can, for one, be produced without biology, although on Earth biology is the major source. Conditions on other planets, however, might be different, producing lots of oxygen without life.
And then there’s the troubling reality that for most of the time there has been life on Earth, there would not have been enough oxygen produced to register as a biosignature. So oxygen brings with it the danger of both a false positive and a false negative.
Wading through the long list of potential other biosignatures is rather like walking along a very wet path and having your boots regularly pulled off as they get captured by the mud. Many possibilities can be put forward, but all seem to contain absolutely confounding problems.
With this reality in mind, a group of several dozen very interdisciplinary scientists came together more than a year ago in an effort to catalogue the many possible biosignatures that have been put forward and then to describe the pros and the cons of each.
“We believe this kind of effort is essential and needs to be done now,” said Edward Schwieterman, an astronomy and astrobiology researcher at the University of California, Riverside (UCR).
“Not because we have the technology now to identify these possible biosignatures light years away, but because the space and ground-based telescopes of the future need to be designed so they can identify them. ”
“It’s part of what may turn out to be a very long road to learning whether or not we are alone in the universe”.
Artistic representations of some of the exoplanets detected so far with the greatest potential to support liquid surface water, based on their size and orbit. All of them are larger than Earth and their composition and habitability remains unclear. They are ranked here from closest to farthest from Earth.
