But what if alien life uses somewhat different chemistry to ours?
We can probe the atmosphere of an exoplanet when it passes in front of its star.
Documenting exoplanet atmospheres is one of the goals of the much-delayedJames Webb Space Telescope.
That is the case on Earth.
Our planets atmosphere contains methane (CH4), which naturally reacts with oxygen to make carbon dioxide.
But the methane is kept topped up by biological processes.
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These may not have any free oxygen, because hydrogen and oxygen make a highly flammable mixture.
The hydrogen-filled Hindenberg airship destroyed by fire in 1937.
Such a fire could not happen on a world with an oxygen-free hydrogen atmosphere.
Murray Becker/Associated Press
Hydrogen is the lightest of all molecules and escapes to space easily.
Hydrogen-breathing in the lab
The authors carried out laboratory experiments in which they demonstrated that the bacteriumE.
They demonstrated the same for a variety of yeast.
Spinoloricus, a tiny but multicellular organism that apparently requires no oxygen to live.
Scale bar is 50 micrometres.
Biosignature gases
The study did make an important discovery though.
The researchers demonstrated that there is an astonishing diversity of dozens of gases produced by products inE.
This boosts our chances of recognizing life signs at an exoplanet you have to know what to look for.
That said, metabolic processes that use hydrogen are less efficient than those using oxygen.
However,hydrogen breathing lifeis already an established concept so far as astrobiologists are concerned.
The authors shy away from considering the chances of finding life in giant gas planets like Jupiter.
