Tuesday, October 26, 2010

Two Planets, Each Orbiting the Same Two Stars

"Surprise Discovery: Two Planets, Two Stars, One System"
Space.com (October 26, 2010)

"Two massive Jupiter-like planets were recently discovered orbiting around two extremely close sister stars – an unexpected find, given the disturbing gravitational effects within most binary star systems that usually disrupt planets from forming.

"The alien planets were found to orbit around the binary star system NN Serpentis, which is located about 1,670 light-years from Earth.

"The more massive of the two stars is a very small white dwarf – the burnt-out remnant that is left over when a sun-like star dies. The star is 2.3 times the diameter of Earth, but has a temperature of more than 89,500 degrees Fahrenheit (49,700 degrees Celsius) – almost nine times hotter than the surface of the sun.

"The other star in the pair is a larger but cooler star, with a mass only one-tenth that of the sun. The two stars are joined in a very tight mutual orbit...."

The stars are lined up so that they eclipse each other, as seen from Earth. That made very precise measurements of their orbit possible. That helped astronomers spot the planets.

"...The larger planet in the system is about 5.9 times more massive than Jupiter. It orbits the binary stars every 15.5 Earth years at a staggering distance of roughly 558 million miles. Closer in, the second planet orbits every the binary pair every 7.75 Earth years, and is about 1.6 times more massive than Jupiter.

"An international team of astronomers detected the planetary system using a wide variety of observations taken over two decades from several ground-based telescopes...."

That white dwarf star shows that NN Serpentis went through rapid changes recently. "Recently" in the cosmological sense, anyway.

There are at least two possible ways that the planets of NN Serpentis would have been involved in the more massive star running out of hydrogen, expanding into a red giant, and then shrinking to its present size.

They might have had their orbits changed - a lot.

Or the planets might be only about a million years old: formed from material thrown off by the red giant star.

Either way, there's a whole lot more to be learned about NN Serpentis.


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