In the last decade we have discovered thousands of planets outside our solar system and have learned that rocky, temperate worlds are numerous in our galaxy. The next step will involve asking even bigger questions. Could some of these planets host life? And if so, will we be able to recognise life elsewhere if we see it?
A group of leading researchers in astronomy, biology and geology have come together under NASA’s Nexus for Exoplanet System Science, or NExSS, to take stock of our knowledge in the search for life on distant planets and to lay the groundwork for moving the related sciences forward.
“We’re moving from theorizing about life elsewhere in our galaxy to a robust science that will eventually give us the answer we seek to that profound question: Are we alone?” said Martin Still, NASA exoplanet scientist at Headquarters, Washington.
In a set of five review papers published last week in the scientific journal Astrobiology, NExSS scientists took an inventory of the most promising signs of life, called biosignatures. They considered how to interpret the presence of biosignatures, should we detect them on distant worlds. A primary concern is ensuring the science is strong enough to distinguish a living world from a barren planet masquerading as one.
The assessment comes as a new generation of space and ground-based telescopes are in development. NASA’s James Webb Space Telescope will characterise the atmospheres of some of the first small, rocky planets.
Through their work with NExSS, scientists aim to identify the instruments needed to detect potential life for future NASA flagship missions. The detection of atmospheric signatures of a few potentially habitable planets may possibly come before 2030, although whether the planets are truly habitable or have life will require more in-depth study.
Since we won’t be able to visit distant planets and collect samples anytime soon, the light that a telescope observes will be all we have in the search for life outside our solar system. Rather than measuring a single characteristic, the NExSS scientists argue that we should be looking at a suite of traits. A planet must show itself capable of supporting life through its features, and those of its parent star.
The NExSS scientists will create a framework that can quantify how likely it is that a planet has life, based on all the available evidence. With the observation of many planets, scientists may begin to more broadly classify the “living worlds” that show common characteristics of life, versus the “non-living worlds.”