An international team of astronomers has discovered a bigger version of Earth locked in an orbital tug-of-war with a much larger, Neptune-sized planet as they orbit very close to each other around the same star about 1,200 light years from Earth.
Few nighttime sights 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.
“These two worlds are having close encounters,” said Dr Josh Carter, a Hubble Fellow at the Harvard-Smithsonian Center for Astrophysics and lead author of a paper published online in Science Express. “They are the closest to each other of any planetary system we’ve found,” added co-author Dr Eric Agol of the University of Washington.
The team spotted the planets in data from NASA’s Kepler spacecraft, which can detect a planet when it passes in front of, and briefly reduces the light coming from, its parent star.
The newfound 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 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. Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets.
The researchers are struggling to understand how these two very different worlds ended up in such close orbits. Within our solar system, rocky planets reside close to the Sun while the gas giants remain distant.
Although Kepler-36 is the first planetary system found to experience such close encounters, it undoubtedly won’t be the last.
“We’re wondering how many more like this are out there,” said Dr Agol. “We found this one on a first quick look,” added Dr Carter. “We’re now combing through the Kepler data to try to locate more.”
Bibliographic information: Carter J.A. et al. 2012. Kepler-36: A Pair of Planets with Neighboring Orbits and Dissimilar Densities. Science. Published online June 21 2012; doi: 10.1126/science.1223269