Six is a crowd: The tightly packed Kepler-11 system has five planets circling a sun-like star, all of them in orbits smaller than that of Mercury. A sixth planet in the system is just slightly more distant. Our solar system is roomy by comparison.
Far from the star: The 1RXS 1609 system is as different as can be from Kepler-11: the system’s star has a planet eight times the size of Jupiter with an orbital radius of about 50 billion kilometres – about 330 times that of Earth. Scientists struggle to explain how a planet that size could form at that distance, leading to theories that it might have been flung to the outer reaches through interactions with other bodies in the system.
Make mine a double: In a classic scene from the movie Star Wars, two suns set over the desert planet of Tatooine. It’s no desert planet, but scientists have located a cold gaseous world about 200 light years from Earth that orbits a pair of stars. If life existed in the inhospitable world of the Kepler-16 system, it would be treated to just such a double sunset.
Water world: Though oceans cover about 70 per cent of the Earth’s surface, they make up less than one per cent of the Earth’s total mass. In contrast, liquid water may account for three-quarters of the mass of planet GJ 1214b. One model suggests that the planet is ocean from pole to pole. This “Super-Earth” is only about 2.5 times the diameter of our world, and planets this size or smaller are prime suspects in the search for extraterrestrial life.