Astrophys. J. 686, 1341–1348 (2008)

A tiny bit of light from an extrasolar 'hot Jupiter' has allowed astronomers to speculate about the diversity of the atmospheres of similar planets.

David Charbonneau of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and his colleagues used the Spitzer Space Telescope to observe a relatively nearby hot Jupiter before and after a 'secondary transit'. These occur as a planet goes behind a star. The number of photons detected before and after the eclipse is compared with the number detected during the eclipse, and the difference is the number that can be attributed to the planet itself.

Charbonneau's team discerned that the hot Jupiter emitted less light in three spectral bands associated with water than in surrounding bands, contrary to findings from another hot Jupiter. This suggests that there are at least two types of hot-Jupiter atmosphere: one that gets cooler with altitude, and another that has a hot layer high up.