Astronomers spy two planets orbiting distant star in close proximity

22 Jun 2012

An artist's conception shows Kepler-36c as it might look from the surface of neighbouring Kepler-36b. Image by Harvard-Smithsonian Center for Astrophysics/David Aguilar

Astronomers at Harvard University and University of Washington are claiming to have found two planets, one like a rocky ‘super Earth’ and the other like a much larger Neptune planet, orbiting closely to each other around the same star about 1,200 light years from Earth.

According to the scientists these are the closest two planets to each other that have ever been found.

Their findings have just been published in Science Express, the online edition of the journal Science.

NASA, the Space Telescope Science Institute and the National Science Foundation funded the research.

According to the astronomers, who used data from NASA’s Kepler spacecraft as part of their research, the two planets almost occupy the same orbital place, and come within nearly 1.9m kilometres of one another on their closest approach.

They said this is five times closer than the Earth-moon distance and 20 times closer than any two planets in our solar system.

The scientists stumbled across the unusual planetary system via asteroseismology – the study of stars by observing their natural oscillations.

The Harvard-Smithsonian Center for Astrophysics (CfA) said the system contains two planets circling a subgiant star much like the sun, except several billion years older.

The inner world, Kepler-36b, is being described as a rocky planet 1.5 times the size of Earth and weighing 4.5 times as much. The scientists said it orbits about every 14 days at an average distance of less than 17.7m kilometres.

‘Hot Neptune’ and a rocky Earth-like planet

Meanwhile, the outer planet Kepler-36c, is being termed a gaseous one that’s 3.7 times the size of Earth and weighs eight times as much. Describing this planet as a ‘hot Neptune’, the astronomers said it orbits once each 16 days at a distance of 19m kilometres.

However, Eric Agol, a University of Washington astronomy professor and co-lead author of a paper, said that the timing of the two planets’ orbits means there isn’t a chance of them ever colliding.

“These are the closest two planets to one another that have ever been found,” Agol said. “The bigger planet is pushing the smaller planet around more, so the smaller planet was harder to find.”

Now the researchers are aiming to find out how these two different worlds ended up in such close orbits.

They said Kepler-36b is the first planetary system ever found to experience such close encounters, and it probably won’t be the last.

“We’re wondering how many more like this are out there,” said Agol.

Carmel Doyle was a long-time reporter with Silicon Republic