The new discovery of six alien planets orbiting a sunlike star may be only a small part of the data released Wednesday from NASA's planet-hunting Kepler mission, but it is significant as the most tightly packed planetary arrangement around a single star yet discovered.
The six planets orbiting Kepler-11 are all larger than Earth, with the largest ones comparable in size to Uranus and Neptune. As far as exoplanets go, these are relatively small worlds.
Kepler-11 is located about 2,000 light-years from Earth. Astronomers used observations made by the Kepler spacecraft to detect the six planets that transit — pass in front of — the star.
The innermost planet, Kepler-11b, is 10 times closer to its star than Earth is to the sun. Moving outward, the other planets are Kepler-11c, Kepler-11d, Kepler-11e, Kepler-11f and the outermost planet, Kepler-11g, which is half as far from its star as Earth is from the sun.
None of the extrasolar planets are inside the so-called "habitable zone" – orbits where water could exist as a liquid on their surfaces, scientists said.
The five inner planets in the Kepler-11 system range in size from 2.3 to 13.5 times the mass of Earth. The orbits of all five would fit inside the orbit of Mercury in our solar system, and all of them circle their star in fewer than 50 Earth days.
The sixth planet is the largest of the group and has an undetermined mass. Its orbit is smaller than Venus', and it completes one orbit every 118 days.
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