Astrophysics

Chaotic Planets

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Science  17 Aug 2012:
Vol. 337, Issue 6096, pp. 779
DOI: 10.1126/science.337.6096.779-c
CREDIT: CREDIT: HARVARD-SMITHSONIAN CENTER FOR ASTROPHYSICS/DAVID AGUILAR

It may not seem so, but the orbits of the planets in our solar system are chaotic, meaning that they are unpredictable beyond a characteristic time scale, known as the Lyapunov time, which in the case of the solar system's inner planets is about 5 million years. Deck et al. now show that the orbits of the two planets in the Kepler-36 system are chaotic, with a Lyapunov time of less than 10 years. The orbits of Saturn's moons Prometheus and Pandora are the only other ones known to show chaos on such a humanly observable time scale.

The two planets orbit a distant star, which has a mass similar to that of the Sun and is among the 156,000 stars regularly monitored by NASA's Kepler space telescope. The planets have masses around 4 and 8 times that of Earth and orbit so close to one another that the angular size of the heavier planet as seen from the lighter planet would be 2.5 times as large as the full Moon viewed from Earth (see Carter et al., Reports, 3 August 2012, p. 556; published online 21 June 2012). The authors suggest that the orbital chaos is a consequence of mutual gravitational interactions between the two planets.

Astrophys. J. 755, L21 (2012).

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