Over the last decade, we have discovered thousands of planets outside our solar system and learned that rocky tempered worlds are many in our galaxy. The next step will mean asking even bigger questions. Can any of these planets host life? And if so, can we recognize life elsewhere if we see it?
A group of leading researchers in astronomy, biology and geology have been gathered under NASA's Nexus for Exoplanet System Science or NExSS to find out our knowledge in the quest for life on remote planets and to lay the foundations for moving related science forward.
"We move from the theory of life elsewhere in our galaxy to a robust science that eventually gives us the answer we are looking for the deep question: Are we alone?" said Martin Still, an exoplanet researcher at NASA's headquarters in Washington.
In a set of five review papers published last week in the scientific journal Astrobiology NExSS researchers took a list of the most promising characters of life, called biosignatures. The authors contain four scientists from NASA's Jet Propulsion Laboratory in Pasadena, California. They considered how to interpret the presence of biosignatures, if we were to discover them in distant worlds. A primary concern is to ensure that science is strong enough to distinguish a living world from a bare planet masked as one.
The assessment comes as a new generation of space and ground-based telescopes are in development. NASA's James Web space telescope will characterize the atmosphere of some of the first small rocky planets. There are plans for other observers – such as the Giant Magellan Telescope and Extremely Large Telescope, both in Chile – to have sophisticated instruments that can detect the first biosignatures in distant worlds.
Through its work with NExSS, researchers are striving to identify the instruments needed to detect potential lives for future NASA flagship missions. The detection of atmospheric signatures of some potentially habitable planets may come before 2030, although determining whether the planets are really habitable or have lives will require more in-depth studies.
Since we will not be able to visit remote planets and collect samples at any time soon, the light a telescope observes will be all we have in the search for life beyond our solar system. Telescopes can examine the light that reflects a distant world to show us different types of gases in the atmosphere and their "seasonal" variations, as well as colors like green that can indicate life.
These types of biosignatures can all be seen on our fertile soil from space, but the new worlds we are investigating will differ significantly. For example, many of the promising planets we found are around cooler stars that emit light in the infrared spectrum, unlike our sun's high emission of visible light.