The Ocean Smells Like Life. A Planet 124 Light-Years Away Does Too.

Using the James Webb Space Telescope, a British-American research team detected signs of two chemicals in the atmosphere of an exoplanet called K2-18b. Dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) are gases that, on Earth, are produced only by life, mostly microscopic marine algae called phytoplankton. The researchers are calling it the strongest evidence yet of life beyond our solar system.

The smell of the ocean, apparently, travels further than anyone thought.

K2-18b is more than eight times the mass of Earth and sits in a "Goldilocks zone" around its star, neither too hot nor too cold to sustain liquid water, which is considered the most important ingredient for life as we know it. In 2023, the Webb telescope had already detected methane and carbon dioxide in K2-18b's atmosphere. It also picked up a weak DMS signal, which sent researchers back for a second look using a different instrument. They found much stronger signs of both chemicals, though still well below the five-sigma threshold scientists require to call something a confirmed discovery.

The gases were detected at atmospheric concentrations of more than 10 parts per million. "For reference, this is thousands of times higher than their concentrations in the Earth's atmosphere, and cannot be explained without biological activity based on existing knowledge," said Cambridge astrophysicist Nikku Madhusudhan.

Skeptics note that the current detection sits at three-sigma confidence, and that K2-18b has a history of three-sigma detections that "completely vanished when subject to closer scrutiny," according to University of Michigan astronomer Ryan MacDonald. Separately, scientists found DMS on a cold, lifeless comet in 2024, a discovery that raises real questions about whether the molecule is as reliable a biosignature as once assumed.

Madhusudhan estimated it would take just 16 to 24 more hours of Webb's time to confirm or challenge the findings.

We have been waiting longer than that.

Read the full story at Reuters, April 16, 2025

Hot Take: The planet's ocean (if it exists, if it's not a magma pit and if the signal holds) would be filled with something like phytoplankton, which means the most profound discovery in human history would also be, chemically speaking, the thing that makes the sea smell. There is something philosophically correct about that.