Nasa's Kepler Spacecraft Discovers Extraordinary New Planetary System

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After their first confirmed rocky planet, Nasa now found what they assume to be their first "Earth-sized" planet located in the habitable zone of its planetary system.

Scientists using NASA's Kepler, a space telescope, recently discovered six planets made of a mix of rock and gases orbiting a single sun-like star, known as Kepler-11, which is located approximately 2,000 light years from Earth.

"The Kepler-11 planetary system is amazing," said Jack Lissauer, a planetary scientist and a Kepler science team member at NASA's Ames Research Center, Moffett Field, Calif. "It’s amazingly compact, it’s amazingly flat, there’s an amazingly large number of big planets orbiting close to their star - we didn’t know such systems could even exist."

2k ligh years from here, it's a long way. As a reference, Proxima Centauri is currently the closest star to the sun at about 4.24 light years. It definitely sounds like they looked for such a system for a pretty long time. They explain later in the article why such systems seem to be so rare, or perhaps so hard to find.

"By measuring the sizes and masses of the five inner planets, we have determined they are among the smallest confirmed exoplanets, or planets beyond our solar system," said Lissauer. "These 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."

I wonder if they have any way to know right now what are those gases on these planets. Even if they were able to detect a liquid, could they know if it's water or something else ? I wonder what they are able to do right now. After all, the chances to find another planet with breathable air is so thin, it's really no big deal not to know exactly what it's made of. Besides, it's so far away from here!

According to Lissauer, Kepler-11 is a remarkable planetary system whose architecture and dynamics provide clues about its formation. The planets Kepler-11d, Kepler-11e and Kepler-11f have a significant amount of light gas, which Lissauer says indicates that at least these three planets formed early in the history of the planetary system, within a few million years.

http://www.nasa.gov/mission_pages/kepler/news/new_planetary_system.html