The planets in the new system are packed together as densely as fans in a mosh pit. Five planets sit practically on top of each other as they circle their star, called Kepler-11; a sixth circles farther out. Two of the planets lie closer together than any other known pair of planets outside our solar system.
"There's only word" to describe the new solar system, NASA's Jack Lissauer said at a news conference today, and it's "supercalifragilisticexpialidocious."
The six planets of Kepler-11 may be among the latest entries on the list of "extrasolar" planets -- those outside our own solar system -- but they won't be the last.
Scientists today revealed that NASA's Kepler spacecraft, which found Kepler-11's planets, has to date spotted more than 1,200 potential planets. Astronomers need to confirm the existence of each of the new candidate planets, some of which will turn out to be false leads. But many others are likely to be verified as actual worlds orbiting other stars -- the first step, scientifically, toward figuring out where to look for life elsewhere in the universe.
Five of those candidate planets are roughly the size of Earth and could contain liquid water, but it will take "patience ... and lots of money" to find out whether those five harbor life, NASA's William Borucki said.
Even in the growing collection of new planets, the Kepler-11 system, which was described in a study published in Thursday's issue of the journal Nature, stands out. For starters there's its size. Kepler-11 boasts at least six planets, many more than most systems, and it may have even more planets that scientists have yet to detect.
It was "shocking" to find six planets orbiting one star, the University of Florida's Eric Ford, an author of the Nature study, told AOL News. He described his team's reaction as the planet count went higher and higher: "There's a second. Oh, there's a third. Oh, there's a fourth! When does it stop?"
Then there's the dense concentration of the planets. Five of Kepler-11's planets circle it more tightly than our sun is circled by its nearest planet, Mercury.
The planets of Kepler-11 are squashed together so compactly that "at first glance, you think, 'Oh, my God, how is this possible?'" says astronomer Christophe Lovis of the University of Geneva, who was not associated with the new study.
Then there's the planets' size. Five are larger than Earth but smaller than Uranus, the next-biggest planet orbiting the sun.
The Kepler-11 grouping is so unusual that it can't be explained by the old theories of how solar systems are born, says NASA's Lissauer, leader of the new study and a specialist in planetary formation.
"Something a little different has to be going on here," he says. "This is sending me back to the drawing board."