Alien life could be found by methane in a planet’s atmosphere, scientists say
Methane is usually broken down in the atmosphere so a high presence of the gas could indicate alien life is replenishing it
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Methane could be the first indication of life beyond Earth, scientists say.
New research from UC Santa Cruz suggests that the gas could be a key ‘biosignature’ – an indicator of life on another planet.
Other biosignatures include nitrogen dioxide gas, which is produced on Earth by burning fossil fuels, and the oxygen that we breathe.
It is hoped that these indicators could be detected by the James Webb Space Telescope that was launched last December.
But while oxygen might be “talked about as one of the best biosignatures,” said Maggie Thompson, a graduate student in astronomy and astrophysics at UC Santa Cruz, “it’s probably going to be hard to detect with JWST.”
Methane is also unstable in the atmosphere – broken down by photochemical reactions. This means that if the gas is detected, something has to be replenishing it.
Moreover, while methane could be a biosignature, there are a variety of non-biological sources for the gas such as volcanos, hydrothermal vents, and comet or asteroid impacts, that need to be assessed before assuming the source is alien.
“If you detect a lot of methane on a rocky planet, you typically need a massive source to explain that,” said co-author Joshua Krissansen-Totton, a Sagan Fellow at UCSC. “We know biological activity creates large amounts of methane on Earth, and probably did on the early Earth as well because making methane is a fairly easy thing to do metabolically.”
Nonbiological sources would not be able to produce that much methane without giving themselves away. Volcanos would add methane but also carbon monoxide, whereas biological activity consumes carbon monoxide.
“One molecule is not going to give you the answer – you have to take into account the planet’s full context,” Ms Thompson said.
“Methane is one piece of the puzzle, but to determine if there is life on a planet you have to consider its geochemistry, how it’s interacting with its star, and the many processes that can affect a planet’s atmosphere on geologic timescales.”
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