Does Our Sun Have A Binary Companion?
Although highly speculative at best, some people think our Sun's binary companion - called the Nemesis Star - may help to explain the periodic extinctions throughout our planet's long history.
According to the hypothesis advocated by Richard Muller, the Sun and Nemesis Star revolve around one another in a period of about 30 million years. When the Nemesis Star passes through the theoretical Oort Cloud, the gravitational disturbance of this red dwarf - or possible brown dwarf - star launches an array of comets that bombards our planet in these approximate 30 million year periods.
So, according to the speculation, the Nemesis Star may be responsible for long-period comets, and a distant Planet X at the "cliff" of the Kuiper Belt could be the source for short-term comets. For more details, listen to the wonderful program at Astronomy Cast.
Of course, the speculation hardly ends here. It's also suggested that a hypothetical gas giant planet in the Oort Cloud - nicknamed Tyche - as a source for long-period comets.
copyright 2013 by Bruce McClure