JWST could expose alien biosignatures on hazy exoplanets | by Ethan Siegel | Starts With A Bang! | Sep, 2025
The most common type of exoplanet is neither Earth-sized nor Neptune-sized, but in between. Could these haze-rich worlds house alien life?
As recently as 1990, we hadn’t yet discovered a single planet around another star beyond our Solar System. When we thought about finding an inhabited world out there in the Milky Way, we had only the worlds of our Solar System — Earth, Venus, Mars, Neptune, Titan, Pluto, Enceladus, Triton, and Jupiter’s moons — to consider as potential analogues. Now in 2025, however, we’re closing in on an incredible 6000 confirmed exoplanets, and we’ve learned that the most common type of world that we know of isn’t represented at all in our Solar System: a class of worlds known as super-Earths and mini-Neptunes. These exoplanets, often rich in atmospheric hazes, are the most abundant species of world known at present.
Could some of these haze-rich exoplanets have something remarkable within their atmospheres? Are they rich in organic molecules, do those molecules undergo a complex series of chemical reactions, and could there be even biological processes taking place? Even here in the JWST era, we’re still struggling to make unambiguous sense of the observations that it’s acquiring of these alien worlds…
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