K2-18b is two and a half times the size of Earth and is seven hundred trillion miles away from us.
JWST is so powerful that it can analyse the chemical composition of the planet's atmosphere from the light that passes through from the small red Sun it orbits.
The Cambridge group has found that the atmosphere seems to contain the chemical signature of at least one of two molecules that are associated with life: dimethyl sulphide (DMS) and dimethyl disulphide (DMDS). On Earth, these gases are produced by marine phytoplankton and bacteria.
Whoa. But also:
"Even with that certainty, there is still the question of what is the origin of this gas," she told BBC News.
If it ends up being just a finding that organic compounds can be found on other planets, that's still amazing.