The discovery of a planetary "odd couple" is broadening the way scientists think about planetary migration.
Scientists at the Harvard Smithsonian Center for Astrophysics and University of Washington discovered two planets of very different sizes and makeups orbiting Kepler-36, a sun-like star under nearly continuous surveillance by the Kepler spacecraft.
"This is kind of an extreme system in that the planets are relatively closely spaced in their orbits but their compositions are quite disparate," said Josh Carter, Hubble Fellow at the Harvard Smithsonian Center for Astrophysics who discovered the smaller planet.
"They're quite the odd couple."
The planet closer to Kepler-36, is thought to be small, rocky and not too unusual on its own accord. The larger planet is more puzzling to scientists. It has a gaseous atmosphere typically seen in outlier planets.
According to a report released detailing the discovery in the journal Science, the loss of light caused when the smaller planet orbits Kepler-36 is only 17% as large as the loss of the light that occurs when the larger planet crosses Kepler-36's path. The timing is also substantially different - so much so that the discovery was initially overlooked.
"What could have happened here is that the outer planet that's farther away from the star, probably formed farther away," Carter said. As orbital neighbors, he said they "stick out like a sore thumb."
Scientists are now trying to determine just how the larger gaseous planet ended up where it did. In doing so they hope to better understand the environments in which types of planets can be formed or how they travel.
"It's useful to know because it weighs in on the prevalence of planets in the galaxy," Carter said.