Sun's Nemesis Pelted Earth with Comets, Study Suggests
By Leslie Mullen
Astrobiology Magazine
posted: 11 March 2010

A dark object may be lurking near our solar system, occasionally kicking comets in our direction. 

Nicknamed "Nemesis" or "The Death Star," this undetected object could be a red or brown dwarf star, or an even darker presence several times the mass of Jupiter.

Why do scientists think something could be hidden beyond the edge of our solar system? Originally, Nemesis was suggested as a way to explain a cycle of mass extinctions on Earth.

The Footprint of Nemesis

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." 

Perhaps a massive unseen object is responsible for Sedna's mystifying orbit, its gravitational influence keeping Sedna fixed in that far-distant portion of space. 

"My surveys have always looked for objects closer and thus moving faster," Brown said to Astrobiology Magazine. "I would have easily overlooked something so distant and slow moving as Nemesis."  

John Matese, Emeritus Professor of Physics at the University of Louisiana at Lafayette, suspects Nemesis exists for another reason. The comets in the inner solar system seem to mostly come from the same region of the Oort Cloud, and Matese 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. 

...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. 

"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.

Even if Nemesis is not found, the WISE telescope will help shed light on the darkest corners of the solar system. The telescope can be used to search for dwarf planets like Pluto that orbit the Sun off the solar system's ecliptic plane. The objects that make up the Oort Cloud are too small and far away for WISE to see, but it will be able to track potentially dangerous comets and asteroids closer to home.

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