Episode 02 · Astrobiology
The strongest hint of alien life yet
A telescope caught a possible whiff of a life-made gas on a world 124 light-years away — and ignited a scientific brawl.
Prof. Nikku Madhusudhan · University of Cambridge
Peer-reviewed in The Astrophysical Journal Letters (2025) · JWST observations of K2‑18b
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Scientists pointed the James Webb Space Telescope at a planet 124 light-years away and caught a faint chemical clue that, on Earth, usually means life.
Here’s the trick: when a planet passes in front of its star, a little starlight filters through its atmosphere. Different gases absorb different colors, leaving “fingerprints.” In K2‑18b’s fingerprints, the team reported a possible trace of dimethyl sulfide (DMS) — a gas that on Earth is belched out almost entirely by ocean plankton. The planet may even be a “Hycean” world: a deep ocean under a thick hydrogen sky.
But hold the alien parade. The signal was faint (about “3‑sigma” — promising, but below the bar scientists need), other teams couldn’t reproduce it, and DMS can form without life. It’s the strongest hint we’ve had — and still just a hint.
Jargon decoder
Exoplanet
A planet that orbits another star, not our Sun.
Habitable zone
The band around a star that’s not too hot or cold for liquid water.
Hycean world
A possible ocean planet wrapped in a thick hydrogen atmosphere.
Biosignature
A sign — often a gas — that hints life might be present.
Dimethyl sulfide (DMS)
A gas made mostly by ocean life on Earth.
Transit spectroscopy
Reading starlight through a planet’s air to tell which gases are there.
“3‑sigma”
A confidence level — promising, but below the “5‑sigma” bar needed to call it a discovery.
Light-year
The distance light travels in a year — about 9 trillion km.
Keep in mind
This is a ~3‑sigma hint, below the 5‑sigma standard for a discovery. Independent teams couldn’t confirm the signal, and DMS can form without life. Exciting — but not evidence of aliens.
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