Double star's exoplanets found

A nearby double-star owns two planets, astronomers report Friday, ones that may have survived some stellar ups-and-downs in their solar system.

In the current Astronomy & Astrophysics journal, a team led by Klaus Beuermann of Germany's Georg-August-Universit├Ąt, reports that two Jupiter-sized planets circle the two stars in the NN Serpentis solar system, some 1,670 light years away (one light year is about 5.9 trillion miles.) The team re-analyzed light collected from the two stars from 1988 to 2010 to find signs of the two planets eclipsing the stars.

Some of the images were collected from University of Texas at Austin telescopes manned by astronomer Don Winget. A university statement on the planets says:

Due to a fortunate accident, Earth lies in the same plane as this binary star system, so every 3 hours and 7 minutes we can see the eclipse which occurs when the larger star moves in front of the smaller one. The resulting dramatic change in the brightness of the system acts like a highly precise clock. Using the eclipses as tics of this clock, the team of astronomers was able to detect changes in the timings of the tics, which reveal the presence of two planets orbiting the pair of stars.

The more massive planet is about 5.9 times more massive than Jupiter. It orbits the binary star every 15.5 years at a distance 6 Astronomical Units. (One AU is the Earth-Sun distance of 93 million miles.) Closer in, the other planet orbits every 7.75 years and is about 1.6 times more massive than Jupiter.

Binary stars are generally thought inhospitable to planets, as their motions disturb the orbits of smaller satellites. The two stars in NN Serpentis are the remains of one star bloating up into a red giant and then shedding much of its mass over a century too turn into a small white dwarf, which would have sent planets out in longer orbits around the stars. Alternately, the planets may have formed from the ruins of the red dwarf gobbling up any earlier planets in the system, making them only about a million years old.

By Dan Vergano


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