Astronomy

Too Close for Comfort?

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Science  21 May 2010:
Vol. 328, Issue 5981, pp. 955
DOI: 10.1126/science.328.5981.955-d
CREDIT: C. CARREAU/ESA

First detected in 2008, WASP-12b is a planet with a mass 1.4 times that of Jupiter. Unlike Jupiter, though, it orbits very close to its parent star—so close that its period is only 26 hours. Thus, WASP12-b is subject to intense tidal forces and is one of the hottest and most intensely irradiated planets known. To understand the consequences of such close stellar proximity, Fossati et al. observed WASP-12b with the Cosmic Origins Spectrograph recently installed on the Hubble Space Telescope. Analysis of the near-ultraviolet part of the planet's transmission spectrum shows that WASP-12b is surrounded by an extended layer that absorbs light at the wavelengths of neutral sodium, tin, and manganese, as well as singly ionized ytterbium, scandium, manganese, aluminum, vanadium, and magnesium. This layer extends as far as 2.69 times the radius of Jupiter, well beyond the distance within which orbiting material is gravitationally bound to the planet; thus, as previously predicted, the planet is actively losing material to the star. Giant planets, like the ones in our solar system, are not expected to have elements other than hydrogen and helium in their upper atmospheres because there is little vertical mixing. To have such a metal-rich exosphere, WASP-12b must have suffered extreme mixing, possibly induced by the intense stellar irradiation and tidal effects.

Astrophys. J. 714, L222 (2010).

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