On DMS:
- DMS is a very specific configuration that’s rarely the endpoint of non-living chemical cycles.
- The simplicity of DMS doesn’t make it less indicative of life—it actually makes it a very selective molecule, which only shows up in large quantities when life is involved (at least in Earth-like chemistry).
- Until we find a compelling abiotic pathway, high DMS remains a strong biosignature, especially in the context of a planet with a potential ocean and mild temperatures
Possible origins:
We’re looking at some form of life that can:
- Thrive in a hydrogen-rich atmosphere
- Possibly live in or on top of a global ocean
- Generate large amounts of DMS—potentially thousands of times more than Earth
The closest Earth analogy is:
- Marine phytoplankton, particularly species like Emiliania huxleyi, produce DMS as a byproduct of breaking down DMSP, a molecule they use to regulate osmotic pressure and protect against oxidative stress.
- If something similar is happening on K2-18 b, we’d be talking about an ocean teeming with such microbes—perhaps far denser than Earth’s oceans.
Possibly "Giant photosynthetic mats" or sulfuric "algae"
If there’s some landmass or floating structures, maybe the DMS producers are:
- Photosynthetic, sulfur-metabolizing analogues to cyanobacteria
- Living in dense floating colonies or mats like microbial reefs
- Using dimethylated sulfur compounds in their metabolism, and leaking DMS as waste or signaling molecules
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Of course there have been lots of ocean planets in sci-fi literature, but I'm most reminded of the "Pattern Juggler" Planet Ararat from Alastair Reynolds' "Revelation Space" series.
This is incredibly exciting news!