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Beyond Earthly Skies

A Planet on the Verge of Engulfment

18 Dec 2013, 10:35 UTC
A Planet on the Verge of Engulfment Mark A. Garlick
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Figure 1: Artist’s impression of a hot-Jupiter transiting its host star. Credit: Mark A. Garlick.The exoplanet Kepler-91 b orbits around an evolved K3 host star that is in the process of transforming into a red giant. Observations show that Kepler-91 b is a gas-giant planet measuring 0.88 times the mass and 1.38 times the radius of Jupiter. Its host star has 1.3 times the mass and 6.3 times the radius of the Sun. Kepler-91 b circles around its host star in a slightly eccentric, close-in orbit with a period of 6.25 days. Given the planetary mass and radius, the mean density of Kepler-91 b works out to be 0.33 times the density of Jupiter. This low density suggests that Kepler-91 b is somewhat inflated due to the strong stellar irradiation from its host star.Although the orbit of Kepler-91 b is nowhere near the shortest for exoplanets, the sheer size of its host star means that Kepler-91 b is a mere 1.32 stellar radii from the surface of its host star at closest approach. As the host star continues to expand into a red giant, estimates show that Kepler-91 b is expected to be swallowed in less than 55 million years ...

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