"The Kepler Six"

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The exo-planet Kepler-11 system, located approximately 2,000 light years from Earth, sounds like something out of a science fiction blockbutser. It is the most tightly packed planetary system yet discovered. All six of its confirmed planets have orbits smaller than Venus, and five of the six have orbits smaller than Mercury's. The only other star with more than one confirmed transiting planet is Kepler-9, which has three.

"Kepler-11 is a remarkable system whose architecture and dynamics provide clues about its formation," said Jack Lissauer, a planetary scientist and Kepler science team member at Ames. "These six planets are mixtures of rock and gases, possibly including water. The rocky material accounts for most of the planets' mass, while the gas takes up most of their volume. By measuring the sizes and masses of the five inner planets, we determined they are among the lowest mass confirmed planets beyond our solar system."

All of the planets orbiting Kepler-11 are larger than Earth, with the largest ones being comparable in size to Uranus and Neptune. The innermost planet, Kepler-11b, is ten 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.

These six small planets are packed so snugly together that they actually drag each other back and forth, causing their orbits (which range from 10 to 47 days for the five inner planets) to vary by as much as 20 minutes, Seager says. Earth’s year, by comparison, “doesn’t even vary by a nanosecond.” That strange dance was a boon to scientists, who—by measuring each planet’s gravitational tug on its neighbors—could calculate their masses.

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http://www.dailygalaxy.com/my_weblog/2011/02/the-kepler-six-hints-at-the-biggest-story-of-the-century.html