Five papers produced by a two-year interdisciplinary study on finding life beyond Earth provide guidelines on the search for extraterrestrial life in both our solar system and others.
Organized by NASA’s Nexus for Exoplanet System Science (NExSS), the papers include contributions by astrobiologists, planetary scientists, Earth scientists, heliophysicists, astrophysicists, chemists, and biologists.
“For life to be detectable on a distant world, it needs to strongly modify its planet in a way that we can detect. But for us to correctly recognize life’s impact, we also need to understand the planet and star–that environmental context is key,” noted Virginia Meadows of UW and principal investigator of VPL.
More than 3,700 exoplanets have been discovered since 1992. NExSS was created by NASA to draw from various scientific fields in searching for biosignatures, signs of extraterrestrial life.
A key accomplishment of NExSS has been facilitating communication between scientists searching for signs of microbial life on other solar system worlds and those looking for such signs on exoplanets.
The first of the papers, all published in the journal Astrobiology, identifies two types of signals scientists can use to search for life. One comes in the form of a planet’s atmospheric gases, such as oxygen, which can be produced by life ranging from microbes to plants. The other is through the type of light reflected by life forms, such as the colors of leaves.
These signatures can already be seen from Earth orbit. A new generation of telescopes, such as the James Webb Space Telescope (JWST), will let scientists probe exoplanets’ atmospheres.
In the second paper, researchers discuss “false positives” or signals that can erroneously lead scientists to conclude a planet has life, and “false negatives,” where signs of life could be missed. For example, oxygen can be produced by life as well as by non-living processes.
“There are lots of things in the universe that could potentially put two oxygen atoms together, not just photosyntheseis–let’s try to figure out what they are,” Meadows emphasized. “Under what conditions are they more likely to happen, and how can we avoid getting fooled?”
Understanding potential biosignatures is the focus of the third and fourth papers, in which researchers apply lessons learned from Earth to the exploration of other planets. Based on factors such as the chemistry in a planet’s atmosphere, a planet’s climate, and the presence of oceans and continents, scientists can assign a probability score as to whether that planet is likely to harbor life.
Biologists and geologists will have to work together to interpret findings about individual planets to determine whether life can adapt to their particular environments, explained Nancy Kiang, a VPL member and biometeorologist at NASA’s Goddard Institute for Space Studies in New York.
The fifth paper focuses on ground- and space-based telescopes, both current and future, that will be used to search for signs of life beyond Earth.