Can binary terrestrial planets exist?
The possible existence of Earth-like binary planets is being described today at the American Astronomical Society's Division for Planetary Sciences meeting in Tucson, AZ. Two bodies, each of mass similar to Earth, can form a closely orbiting pair under certain conditions present during the formation of planetary systems. This theoretical proposal is completely unlike the Earth-Moon system or Pluto-Charon, where the two bodies are very different in mass, and arises in some "kissing" collisions where two similar mass bodies encounter each other and become a bound system because of the energy lost in the strong tides raised on each other in the encounter. The resulting binary can then persist for billions of years provided it forms well away from the central star, at half an astronomical unit (the distance between the Earth and Sun) or more. This work was presented by undergraduate Keegan Ryan, graduate student Miki Nakajima, and Dr....