A group of scientists who specialize in different fields including biology, astronomy, and geology has compiled the best strategies that can help anticipate and locate life in other worlds as part of NASA's Nexus for Exoplanet System Science (NExSS) initiative.
In a set of five review papers, which was published in the journal Astrobiology, the group took an inventory of biosignatures, the most promising signs of life. The scientists hope that this can help interpret the presence of biosignatures in other worlds. The aim is to ensure that the science is strong enough to distinguish a living world from those that merely masquerade as one.
Most Promising Biosignature Of Life
The scientists said that that oxygen is still the most promising biosignature of life elsewhere albeit the presence of the gas is not a foolproof indicator of life in other worlds.
Abiotic processes are also known to produce oxygen and a planet without detectable levels of oxygen could still be alive such as in the case of Earth prior to the accumulation of oxygen in its atmosphere.
NExSS scientists thus argue that instead of measuring a single characteristics, a suite of traits should be considered. A living planet also needs to show itself to be capable of supporting life through its features and those of its host star.
"Consequently, our ability to interpret both the presence and absence of O2 in an exoplanetary spectrum relies on understanding the environmental context," Mary Parenteau, from NASA's Ames Research Center in Silicon Valley, and colleagues wrote in one of the papers. "Planetary characteristics that may enhance false negatives should be considered when selecting targets for biosignature searches."
Purple Dominated Life Forms
Telescopes that can examine the light that reflect off distant worlds can reveal the kinds of gases in their atmospheres as well as the seasonal variations. They may also show colors like green that may indicate life.
Earth may be dominated by green-colored life forms such as trees in fertile rainforests that host plant and animal life but this is not necessarily the same in other worlds since many differ significantly from Earth. Some are around cooler stars that emit light in the infrared spectrum instead of the visible-light produced by our sun.
"We have to be open to the possibility that life may arise in many contexts in a galaxy with so many diverse worlds - perhaps with purple-colored life instead of the familiar green-dominated life forms on Earth, for example," Parenteau said. "That's why we are considering a broad range of biosignatures."
