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Published online: 3 March 2010 | doi:10.1038/nchina.2010.28

Planetary science: Finding a gas leak on another Jupiter

Felix Cheung

Introduction

© (2010) Nature

The 'gas giant' planet WASP-12b is unlike any other planet scientists have ever seen. It is 1.4 times the mass of Jupiter (M_J), yet it is so close to its host star that it only takes 1.1 days to complete its orbit. Moreover, it has an unexpectedly large radius — 1.8 times that of Jupiter — and an elliptic orbit, which is unusual because close orbits tend to be circular. Douglas Lin and co-workers at Peking University in Beijing, China, and the University of California, USA¹, have now found that WASP-12b is also losing mass to its host star.

The researchers analysed the amount of stellar light blocked by WASP-12b as it transits its host star (see image). They estimated the density of the atmosphere at the planet's surface (inner opaque purple spheroid) and its gravitational equipotential (outer transparent surface) and showed that the star's gravity distorts the planet's surface so that it is not perfectly spherical. Consequently, the way in which WASP-12b scatters stellar photons (orange arrows) and emits its own thermal radiation is slightly different from that of a spherical planet.

Sometimes, the planetary gas of WASP-12b can escape through the inner Lagrange point (marked L₁). The equipotential surface then channels the gas flow (purple arrows) towards the star. The researchers estimated that WASP-12b is losing mass at a rate of about 10⁻⁷M_J per year. They also predicted that the escaped planetary gas forms a tenuous disk around the star, which should emit detectable infrared radiation.

The authors of this work are from:
Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, China; Department of Astronomy, Peking University, Beijing, China; Department of Astronomy and Astrophysics, University of California, Santa Cruz, California, USA.

Reference

1. Li, S. L., Miller, N., Lin, D. N. C. & Fortney, J. J. WASP-12b as a prolate, inflated and disrupting planet from tidal dissipation. Nature 463, 1054–1056, (2010). | Article | OpenURL