Two planets recently discovered by the Kepler Space Telescope orbiting the star Kepler-36 come as close as 1.2 million miles every 97 days. One is a so called "super-Earth" and the other is a gaseous planet about the size of Neptune orbit this a 1,200 light-years from Earth. They are closer than any other known planets making make them visible to each other as disks instead of stars with Kepler-36c appearing Kepler-36b’s sky in 2.5 times the size as our moon as seen from Earth.
The two planets are about 30 times closer than any planets our solar system yet one has a density similar to Earth and the other has a density similar to that of Saturn. This is yet another failure of naturalistic planet formation theories and will likely force a reworking of both planet formation and migration theories.