K2-18 b is a waterworld...?

As we hold tight for more Bird-Gospel news, let's do some sciencin'. Remember Hycean worlds? K2-18 b may be one.

This is one of Kepler Telescope's transits, 120 light years away, habitable-zone. At 8.6 earth-mass, it was presumed to have a thick atmosphere. The James Webb 'scope reads the atmosphere: high methane and carbon dioxide, undetectable ammonia (or carbon monoxide). Well big deal, right; sounds like Titan. But it's warmer than Titan - in fact, with flux 1368 W/m² its orbit approximates Earth irradiance.

The assumption is that there's a waterworld down there. Where's the water in the press-release...? - the arXiv paper explains, it shares a band with the methane, which methane is swamping it, and also the planet has a stratosphere, which is dry. Water condenses into clouds, below that, in the troposphere.

[Most tantalising is dimethyl sulfide. Like phosphine, usually this is made by life - specifically phytoplankton. Although as we found from Venus, at least phosphine can come right out of volcanoes. The dimethyl sulfide isn't a sure thing but it's surer than the (non-)ammonia. FAKE NEWS 4/28/24: It's on 67P. Which is a Cereslike behaving like a comet. NEXT]

QUESTCHINNED 10/20: David Moore ponders instead the "Type C" Titanlike, where carbon rules. I dislike titles with ? at the end but, on occasion, I've already written the title, and don't want to take the whole thing down and rewrite it.