Have Astronomers Finally Found Evidence of Life on K2-18b?

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.

So what changed? 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. So what do I think about the detection of dimethyl sulfide on K2-18b? I think that it stinks.

At least one person has written Answers in Genesis, asking how the JWST could detect a gas in the atmosphere of a planet 124 light-years away. Keep in mind that the JWST is a very large telescope—its mirror is 6.5 meters across. Just 40 years ago, that would have been the largest optical telescope in the world. The JWST operates deeply in the infrared, at wavelengths that are mostly or entirely blocked by the earth’s atmosphere. Like most exoplanets so far discovered, K2-18b transits, or passes in front of, its star once each orbit. As K2-18b transits the star, light from the star passes through the planet’s atmosphere, and the gases in the atmosphere absorb light at certain wavelengths that happen to be in the infrared. Therefore, in the spectrum of the star taken during the transit of K2-18b, astronomers can pick out absorption features of different gases. It isn’t easy to do this, but the large aperture and infrared sensitivity of the JWST make this possible.

There is a long chain of assumptions to get only “simple” life on this exoplanet.

There is a long chain of assumptions to get only “simple” life on this exoplanet. Break any link in the chain, and there is no chance for life on K2-18b. I think that this claim will be contested and probably will be walked back. The reason this sort of thing is rushed to print is that if anyone is the first to detect life, any life, elsewhere in the universe, a Nobel Prize likely will follow. Nobel Prizes rarely go to runners-up, so it is easy to understand the motivation to be the first to report evidence for life on another planet, regardless of how flimsy the evidence may be. Nor is this motivation new. Many of us remember the 1996 report that the Mars rock ALH84001 contained signs of life on Mars. That caused quite a stir in the news three decades ago. Somehow, the hundreds of later papers contesting that conclusion didn’t get as much news coverage. While the idea that ALH84001 indicated that life on Mars has faded, there are still some people who think scientists proved the existence of life on Mars three decades ago. I suspect that the authors of the original paper on this were thinking of a Nobel Prize too.

While the Bible does not address the question whether life exists on other planets, we at Answers in Genesis think that life on other planets is inconsistent with what the Bible teaches us. We are special creations, made in God’s image and in his likeness, to fulfill God’s purposes. So far, astronomers have discovered more than 5,000 exoplanets. If 30 years ago we had asked scientists once we had discovered more than 5,000 exoplanets how many earthlike planets would be among them, most scientists would have opined that the number would be in the hundreds. So far, no planets even remotely resembling earth have been found, confirming our conviction that we are alone in the universe.