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March 16, 2010

Will the NASA WISE Space Telescope Find Nemesis, a Binary Companion Star for the Sun ?

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Astrobiology Magazine - Is our Sun part of a binary star system? An unseen companion star, nicknamed “Nemesis,” may be sending comets towards Earth. If Nemesis exists, NASA’s new WISE telescope should be able to spot it.

Our solar system is surrounded by a vast collection of icy bodies called the Oort Cloud. If our Sun were part of a binary system in which two gravitationally-bound stars orbit a common center of mass, this interaction could disturb the Oort Cloud on a periodic basis, sending comets whizzing towards us.

A recently-discovered dwarf planet, named Sedna, has an extra-long and usual elliptical orbit around the Sun. Sedna is one of the most distant objects yet observed, with an orbit ranging between 76 and 975 AU (where 1 AU is the distance between the Earth and the Sun). Sedna’s orbit is estimated to last between 10.5 to 12 thousand years. Sedna’s discoverer, Mike Brown of Caltech, noted in a Discover magazine article that Sedna’s location doesn’t make sense.

"Sedna shouldn't be there,” said Brown. “There's no way to put Sedna where it is. It never comes close enough to be affected by the Sun, but it never goes far enough away from the Sun to be affected by other stars.”



John Matese (University of Louisiana at Lafayette) thinks the gravitational influence of a solar companion is disrupting that part of the cloud, scattering comets in its wake. His calculations suggest Nemesis is between 3 to 5 times the mass of Jupiter, rather than the 13 Jupiter masses or greater that some scientists think is a necessary quality of a brown dwarf. Even at this smaller mass, however, many astronomers would still classify it as a low mass star rather than a planet, since the circumstances of birth for stars and planets differ.

Richard Muller of the University of California Berkeley first suggested the Nemesis theory, and even wrote a popular science book on the topic. He thinks Nemesis is a red dwarf star 1.5 light years away.

Binary star systems are common in the galaxy. It is estimated that one-third of the stars in the Milky Way are either binary or part of a multiple-star system.

Part of the WISE mission is to search for brown dwarfs, and NASA expects it could find one thousand of the dim stellar objects within 25 light years of our solar system.

Ned Wright, professor of astronomy and physics at UCLA and the principal investigator for the WISE mission, said that WISE will easily see an object with a mass a few times that of Jupiter and located 25,000 AU away, as suggested by Matese.

We may not have an answer to the Nemesis question until mid-2013. WISE needs to scan the sky twice in order to generate the time-lapsed images astronomers use to detect objects in the outer solar system. The change in location of an object between the time of the first scan and the second tells astronomers about the object’s location and orbit. Then comes the long task of analyzing the data.

“I don't suspect we'll have completed the search for candidate objects until mid-2012, and then we may need up to a year of time to complete telescopic follow-up of those objects,” said Kirkpatrick.


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