Two planets in the Kepler-36 system

“These two worlds are having close encounters!” said Josh Carter, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics. Two planets in the Kepler-36 system they are experiencing a conjunction every 97 days on average, separated by less than five Earth-Moon distances.

“They are the closest to each other of any planetary system we’ve found,” added co-author Eric Agol of the University of Washington.

Few nighttime sites offer more drama than the full Moon rising over the horizon. Now imagine that instead of the Moon, a gas giant planet spanning three times more sky loomed over the molten landscape of a lava world. This alien vista exists in the newly discovered two-planet system of Kepler-36.

Carter, Agol and their colleagues report their discovery, in the June 21st Science Express.

They spotted the planets in data from Kepler spacecraft, which can detect a planet when it passes in front of, and briefly reduces the light coming from, its parent star.

The new-found system contains two planets circling a subgiant star much like the Sun except several billion years older. The inner world, Kepler-36b, is a rocky planet 1.5 times the size of Earth and weighing 4.5 times as much. It orbits about every 14 days at an average distance of less than 11 million miles.

The outer world, Kepler-36c, is a gaseous planet 3.7 times the size of Earth and weighing 8 times as much.

This “hot Neptune” orbits once each 16 days at a distance of approx 12 million miles.

The two planets experience a conjunction every 97 days on average. At that time, they are separated by less than 5 Earth-Moon distances. Since Kepler-36c is much larger than the Moon, it presents a spectacular view in its neighbor’s sky. (Coincidentally, the smaller Kepler-36b would appear about the size of the Moon when viewed from Kepler-36c). Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets.

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