Planetary Science

Weather on the Pegasi Planets

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Science  12 Apr 2002:
Vol. 296, Issue 5566, pp. 219
DOI: 10.1126/science.296.5566.219b

Fifteen of the 73 extrasolar planets have nearly circular orbits and are within 0.1 astronomical unit of their solar-type star. These Pegasi planets, named after the first extrasolar planet 51 Peg b, are so close to their parent star that they are bombarded by intense stellar irradiation, which influences atmospheric dynamics and even the size of the planet.

In a pair of papers, Guillot and Showman model the radial temperature variations and atmospheric circulation of the extrasolar gas giant HD209458b, whose radius is known from direct measurement during a stellar transit. They can explain the larger-than-expected radius by proposing that 1% of the stellar radiation is converted in the planet's atmosphere into kinetic energy and then is transported as thermal energy into the convective core. This input of energy would reduce the rate at which the planet cools (and contracts) and allow for lower atmospheric temperatures, in accord with earlier calculations. In addition, the stellar flux in combination with day-night temperature asymmetries (of up to 500 K) could push the planet out of synchronous rotation with its star and generate clouds, winds (of up to 1 km per second), and other heterogeneous features.—LR

Astron. Astrophys.385, 156; 166 (2002).


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