Thursday, December 2, 2010

Evidence of a 'Mini-Nemesis' at The Edge of Our Solar System

It is being referred to as Tyche (Nemesis’ relatively more pleasant sister). Instead of a brown dwarf hiding in the outer reaches of our solar system tossing comets our way, it could be a planet just under 1.5 times the mass of Jupiter. Tyche is suspected of sending about a fifth of the comets our way.

http://www.wired.com/wiredscience/2010/11/oort-cloud-companion

"This idea was a reaction to an earlier notion that a dim brown-dwarf or red-dwarf star, ominously dubbed Nemesis, has pummeled the Earth with deadly comet showers every 30 million years or so. Later research suggested that mass extinctions on Earth don’t line up with the Nemesis predictions, so many astronomers now think that object doesn’t exist.

“But we began to ask, what kind of an object could you hope to infer from the present data that we are seeing?” Matese said. “What could possibly tickle [comets'] orbits and make them come very close to the sun so we could see them?”
...
The cosmic snowballs that form the hearts of comets generally hang out in the Oort Cloud until their orbits are nudged by some outside force. This push could come from one of three things, Matese said. The constant gravitational pull of the Milky Way’s disk can drag comets out of their icy homes and into the inner solar system. A passing star can shake comets loose from the Oort Cloud as it zips by. Or a large companion like Nemesis or Tyche can pull comets out of their comfort zones.

Computational models show that comets in each of these scenarios, when their apparent origins are mapped in space, make a characteristic pattern in the sky.
...
After examining the orbits of more than 100 comets in the Minor Planet Center database, the researchers concluded that 80 percent of comets born in the Oort Cloud were pushed out by the galaxy’s gravity. The remaining 20 percent, however, needed a nudge from a distant object about 1.4 times the mass of Jupiter.

“Something smaller than Jovian mass wouldn’t be strong enough to do the deed,” Matese said. “Something more massive, like a brown dwarf, would give a much stronger signal than the 20 percent we assert.”
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