Creation Moment 5/1/2025 - K2-18b

Hath in these last days spoken unto us by His Son, whom He hath appointed heir of all things, by whom also He made the worlds; Hebrews 1:2

"Exoplanet K2-18b is in the news again. I say that this exoplanet is in the news again because more than five years ago, I responded to a related news story about K2-18b.

The news then was that astronomers had detected water vapor in the atmosphere of this exoplanet. Of course, the presence of water vapor suggests the possibility of liquid water on a planet’s surface, which

we all know is a necessary ingredient for life. However, the study reported back then didn’t emphasize that much. They modeled the atmosphere, and the model indicated that the atmosphere was very cloudy. 

Furthermore, the model suggested that the atmosphere was dominated by hydrogen helium, not nitrogen as the earth’s atmosphere is. A nitrogen-based atmosphere is the gold standard for the possibility of life. 

The astronomers also noted the exoplanet’s low density, indicating that heavier elements also essential for life were probably lacking on K2-18b. Then there is K2-18b’s eccentric orbit around its star. The eccentric orbit causes a 27% change in distance from its red dwarf star, with a stunning 62% change in heating radiation over its 33-day orbit. Overall, K2-18b is not a good candidate for hosting life.

Q: So what changed? 

A: Using the James Webb Space Telescope (JWST), the newest study on K2-18b announced the detection of dimethyl sulfide, a compound claimed can come only from living things (bacteria on earth) and hence is a biosignature. The researchers speculated much about K2-18b, suggesting that it may have a vast ocean that is teaming with life. 

However, this is a preliminary result, which awaits verification. 

--That is, the detection of dimethyl sulfide may be a false signal. 

--And even though dimethyl sulfide is confirmed in the atmosphere of K2-18b, it isn’t true that it is necessarily a biosignature.

Last year, a study reported detection of dimethyl sulfide in Comet 67P/Churyumov-Gerasimenko. Comets hardly are places where life might exist. Furthermore, another study last year discounted dimethyl sulfide as a biosignature. A study published last year suggests that K2-18b may be a gas-rich mini-Neptune (not a super-earth) that lacks any habitable surface. Things are not looking good for life on K2-18b. 

Q: So what do I think about the detection of dimethyl sulfide on K2-18b? 

A: I think that it stinks." 

AIG