APOD: 2019 September 17 - Water Vapor Discovered on Distant Exoplanet

Good morning, Rallypoint. Today's Astronomy Picture of the Day is titled "Water Vapor Discovered on Distant Exoplanet." You may have seen coverage of this in recent news stories. Why is the spectral signature of water vapor so important? As we presently understand it, the presence of liquid water is necessary for life to exist. A planet with water vapor in its atmosphere may have liquid water on its surface.

Planet K2-18b was originally detected by the Kepler Space Telescope in 2015. The recent announcement is based on additional data collected from the Hubble and Spitzer Space Telescopes. These two independent studies concluded that there are significant amounts of water vapor in its atmosphere, a first for an exoplanet in the habitable zone. The habitable zone refers to the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure. Today's featured illustration imagines exoplanet K2-18b on the right, its parent red dwarf star K2-18 on the left, and an unconfirmed sister planet between them.