The discovery of K2-18b is remarkable.

In a study published Sept. 11, 2019, researchers at the University College London released this image to illustrate the detection of water vapor in the atmosphere of exoplanet K2-18b.In a study published Sept. 11, 2019, researchers at the University College London released this image to illustrate the detection of water vapor in the atmosphere of exoplanet K2-18b.(Image: © ESA/Hubble, M. Kornmesser) Water vapor, and likely clouds that rain liquid water, have been discovered in the atmosphere of an exoplanet that lies in the habitable zone of its star. But there’s…