Astronomy: Ozone-like layer in an exoplanet atmosphere.

Abstract

The nature of exoplanetary atmospheres is hotly debated. The thermal spectrum of an exoplanet called a hot Jupiter reveals the presence of an analogue of Earth's ozone layer, although its composition is unknown. See Letter p.58 Earth's atmosphere consists of layers that are partially defined by their temperature. In the troposphere, which is just above the Earth's surface, temperature decreases with altitude, whereas the layer above, the stratosphere, is warmer. Exoplanets could also have stratospheres, but whether they actually do has been an open question. One way to find out is to observe whether molecular species are seen in emission in the planet's thermal spectrum, which would indicate that the overlying layer is hotter than the lower one. Tom Evans et al. report observations of the gas-giant exoplanet WASP-121b, which reveal emission lines of water, from which they conclude that the planet has a stratosphere.