KOI-500

The star KOI-500 is about 1,100 light years away.  It has about the same mass as the Sun, though only three-quarters the diameter, and it's young-- about a billion years old.

The most interesting thing about KOI-500, however, is its planetary system.  Using data from Kepler, astronomers have determined it has at least five planets, each of which is slightly larger than Earth, and each of which orbits its star much closer than Mercury orbits the Sun.  Whereas Mercury zips around the Sun in 88 days, the outermost of the five gets around KOI-500 in 9.5 days.

Scientists think all five planets formed farther away from the star and migrated inward.  The orbits now, however, appear gravitationally interlocked and stable.  Figuring out the history of that system will likely keep theorists busy for quite some time.