Planet the Drake equation, which estimates the number of intelligent, communicating civilizations that exist in the Milky Way. There are exoplanets that are much closer to their parent star than any planet in the Solar System is to the Sun, and there are also exoplanets that are much farther from their star. Mercury, the closest planet to the Sun at 0.4 AU, takes 88 days for an orbit, but the shortest known orbits for exoplanets take only a few hours, e.g. Kepler-70b. The Kepler-11 system has five of its planets in shorter orbits than Mercury's, all of them much more massive
Dark Planet the series' best. It was part of a second set of four books, which were successful enough to allow the range to continue. Dark Planet "Dark Planet" is a BBC Books adventure book written by Davey Moore and is based on the long-running British science fiction television series "Doctor Who". It features the Tenth Doctor and Martha. This one was set on a future version of Earth where society was split in half and some people stayed underground and the rest high above on land dangerously close to the Sun. This is part of the "Decide Your Destiny" series which