Astronomers think that a mixture of carbon dioxide and methane in a planet's atmosphere could be an indicator of life - what's known as a biosignature.

WASP-39b's signal is "halfway to a good biosignature", says Christiansen.

Batalha's team has built a model predicting that the planet's atmosphere also contains water, carbon monoxide and hydrogen sulfide - but little methane.


Ultimately, the detection of life will probably require an observatory even more advanced than Webb.


But, Batalha says,

"this is a really important phase that we need to pass through to be ready for that technology in the future".