Since the James Webb Space Telescope (JWST) came online 18 months ago it has been returning amazing images of spiral nebulae, free-floating exo-planets, massive 13-billion-year-old galaxies and other exotic stellar objects. The images have elicited the phrase “these shouldn’t exist” from more than one astrophysicist, leaving them scratching their heads. The telescope can also probe the very chemistry of the objects that it observes.
In the case of exo-planets, the JWST does this by observing the light that is absorbed by a planet’s atmosphere as it passes in front of its parent star. Analysing the spectrum of the absorbed light reveals tell-tale signs of particular chemicals. And the atmosphere of one particular exo-planet, with the catchy name K2-18b, has caught folks’ attention.
K2-18b was first spotted by the Kepler Telescope back in 2015. Its promising position in the habitable zone around its red dwarf star warranted taking a closer look with the JWST. Sure enough, the JWST’s spectral analysis of K2-18b’s atmosphere has thrown up some tantalising signals.
It almost certainly contains methane and carbon dioxide, both of which are produced by life on Earth. Carbon dioxide is a good sign, but it can be formed from a variety of non-organic processes. Methane would not accumulate in our atmosphere without life, although there are known geological processes that also produce it. But intriguingly, the JWST may also have caught a sniff of dimethyl sulfide, a compound that, as far as we know, is only produced by life.
But we mustn’t get too excited. K2-18b is a very different astronomical beast to our own rocky globe. It more closely resembles Neptune than Earth, and is orbiting a star very different from our own. If there’s one thing we have learned from the mass of data flooding out of the telescope, it is that we should no longer be surprised when we observe distant worlds that don’t fit our current scientific models, based on very narrow observations of our tiny corner of the Universe.
This article is from New Humanist's winter 2023 issue. Subscribe now.
