Tuesday, November 08, 2011

Double sunsets

kw: astronomy, exoplanets, discoveries

Well! I let this one slip by me. Almost two months ago, September 15, 2011, the Kepler Mission folks announced the discovery of a planet similar in size to Saturn, that is orbiting a double star. In this frame from the NASA animation of the system, the larger yellow star is a K-class dwarf half the size of the Sun, and the smaller orange star is an M-class dwarf. They orbit their common center of mass at a distance of 0.22 AU from one another, while the planet's orbital radius is 0.7 AU, about the distance of Venus from the Sun. If you project from the small star through the large star to the brightest dot about 4x their distance, that's the planet. Of course it is much easier to see in the video, where it is moving rapidly.

There has been much debate among scientists (and science fiction aficionados) whether stable planetary orbits around double stars are possible. This demonstrates that such cases are indeed possible. It remains to be seen whether a planet can orbit stably in a double star system when its orbital radius is similar to the distance between the stars. Speculations about looping orbits have abounded for decades.

Given that, from Earth's perspective, the stars are an eclipsing binary, and that the planet also transits both stars, the planet is treated to frequent eclipses and transits of the two stars, and double sunrises or double sunsets must be common. A dense, Saturn-size object is unlikely to have a surface from which the sky can be seen, so anyone visiting the system will have to watch the sky from the surface of a satellite. Both our Jupiter and Saturn have many satellites, so this planet will likely have several to choose from.

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