Vastly Different Planets Found Closely Orbiting Same Star
June 22, 2012

Vastly Different Planets Found Closely Orbiting Same Star

Researchers working on NASA's Kepler Mission have discovered an unlikely pair of planets -- one similar to our planet, and the other roughly the size of Neptune -- locked in a surprisingly close orbit around a distant star located more than a thousand light years from Earth.

The work, which was led by Joshua Carter of the Harvard-Smithsonian Center for Astrophysics (CfA) and University of Washington Associate Professor of Astronomy Eric Agol, discovered that the smaller planet, which was said to be a little larger than Earth, was locked in "an orbital tug-of-war" with the larger planet as they both orbited the same star, the Seattle-based school said in a Thursday press release.

"The planets occupy nearly the same orbital plane and on their closest approach come within about 1.2 million miles of each other -- just five times the Earth-moon distance and about 20 times closer to one another than any two planets in our solar system," the university said. However, as Agol pointed out, despite the fact that this is the closest that researchers have ever observed two planets in relation to each other, the timing of their orbits means that the worlds will never collide with one another.

According to a separate Harvard press release, the inner world, known as Kepler 36-b, is a rocky planet approximately 1 1/2 times the size and 4 1/2 times the weight of Earth. It has an 11 million mile orbit that lasts approximately 14 days. Their findings will be published online Friday in the journal Science Express.

The outer world, on the other hand, is a gaseous planet more than 3 1/2 times the size and more than 8 times the weight of Earth. Kepler-36c, as it has been dubbed, orbits once every 16 days at a distance of 12 million miles. The two worlds experience a conjunction approximately once every 97 days, where they are separated by less than five Earth-Moon distances, the CfA press release reports.

"Small, rocky planets should form in the hot part of the solar system, close to their host star -- like Mercury, Venus and Earth in our Solar System. Bigger, less dense planets -- Jupiter, Uranus -- can only form farther away from their host, where it is cool enough for volatile material like water ice, and methane ice to collect. In some cases, these large planets can migrate close in after they form, during the last stages of planet formation, but in so doing they should eject or destroy the low-mass inner planets," Steve Kawaler, an Iowa State University professor of physics and astronomy and a member of the research team, explained in a statement.

"Here, we have a pair of planets in nearby orbits but with very different densities," he added. "How they both got there and survived is a mystery."

As for the star that the two worlds orbit, Los Angeles Times reporter Thomas H. Maugh II said that Kepler 36 has approximately the same mass as our solar system's sun, but is only one-fourth as dense and is also slightly hotter. It contains slightly less metal, is believed to be a few billion years older than the sun, has entered the sub-giant stage and no longer burns hydrogen at its core, he added.

Image 2 (below): In this artist's conception, a "hot Neptune" known as Kepler-36c looms in the sky of its neighbor, the rocky world Kepler-36b. The two planets have repeated close encounters, experiencing a conjunction every 97 days on average. At that time, they are separated by less than 5 Earth-Moon distances. Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets, which may promote active volcanism on Kepler-36b. Credit: David A. Aguilar (CfA)