Kepler telescope finds two planets sharing the same orbit

Architecture and Dynamics of Kepler’s Candidate Multiple Transiting Planet Systems

by Jack J. Lissauer, Darin Ragozzine, Daniel C. Fabrycky, Jason H. Steffen, Eric B. Ford, Jon M. Jenkins, Avi Shporer, Matthew J. Holman, Jason F. Rowe, Elisa V. Quintana, Natalie M. Batalha, William J. Borucki, Stephen T. Bryson, Douglas A. Caldwell, David Ciardi, Edward W. Dunham, Jonathan J. Fortney, Thomas N. Gautier III, Steve Howell, David G. Koch, David W. Latham, Geoffrey W. Marcy, Robert C. Morehead, Dimitar Sasselov

Astrophysical Journal (arxiv.org/abs/1102.0543).

From the New Scientist:

Room for two (Image: NASA/Ames/JPL-Caltech)

Room for two (Image: NASA/Ames/JPL-Caltech)

Buried in the flood of data from the Kepler telescope is a planetary system unlike any seen before. Two of its apparent planets share the same orbit around their star. If the discovery is confirmed, it would bolster a theory that Earth once shared its orbit with a Mars-sized body that later crashed into it, resulting in the moon’s formation.

The two planets are part of a four-planet system dubbed KOI-730. They circle their sun-like parent star every 9.8 days at exactly the same orbital distance, one permanently about 60 degrees ahead of the other. In the night sky of one planet, the other world must appear as a constant, blazing light, never fading or brightening.

Gravitational “sweet spots” make this possible. When one body (such as a planet) orbits a much more massive body (a star), there are two Lagrange points along the planet’s orbit where a third body can orbit stably. These lie 60 degrees ahead of and 60 degrees behind the smaller object. For example, groups of asteroids called Trojans lie at these points along Jupiter’s orbit.

In theory, matter in a disc of material around a newborn star could coalesce into so-called “co-orbiting” planets, but no one had spotted evidence of this before. “Systems like this are not common, as this is the only one we have seen,” says Jack Lissauer of NASA’s Ames Research Center in Mountain View, California. Lissauer and colleagues describe the KOI-730 system in a paper submitted to the Astrophysical Journal (arxiv.org/abs/1102.0543).

File:Lagrange points2.svg

Lagrange Points: image Wikipedia

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