A second look at the massive data set being generated by the Kepler space telescope has turned up a pair of extra-solar planets that pass so close to each other in their orbits that tidal forces from the larger of them initially concealed the smaller planet.
Researchers at the Harvard-Smithsonian Center for Astrophysics and the University of Washington used a different algorithm -- quasi-periodic pulse detection -- to reexamine the faint dimming in a star's light that Kepler detects when a planet passes in front of it. That turned up a second planet orbiting a star 1,200 light years from Earth in the constellation Cygnus called Kepler-36a.
The space telescope already had discovered one planet there -- a "hot Neptune" designated Kepler 36c that orbits the planet every 16 days at a distance of only 12 million miles. When the new algorithm was applied to the old data, a second planet appears -- Kepler 36b, orbiting a little more than 1 million miles inside the larger planet's orbit every 14 days. That is seven orbits for every that the larger makes.
"These are the closest two planets to one another that have ever been found," says Eric Agol of the University of Washington. "The bigger planet is pushing the smaller planet around more, so the smaller planet was harder to find."
Even at the tiny separation distance of 1.2 million miles Kepler 36b -- which the scientists who found it believe is a rocky planet with a radius 1.5 times that of Earth that is 4.5 times more massive -- would look like the Moon from Earth's surface if you could stand on Kepler 36c.
But 36c has a radius 3.6 times that of Earth, and from the surface of its rocky partner it would appear huge in the dark sky, as in this artist's conception.
Harvard-Smithsonian Center for Astrophysics/David Aguilar
The view would be most spectacular every 97 days on average, when they are in conjunction. The team that found the smaller planet and published the discovery in Science Express expects to find more close pairs orbiting other stars."We found this one on a first quick look," says Joshua Carter, a Hubble fellow at the Harvard-Smithsonian Center. "Now we're combing through the Kepler data to try to locate more."