Image (Left): In a survey of the sky, WISE found more brown dwarfs farther from the sun than it did nearby. In this image of our astronomical back yard, shown from a the view of 30 light-years from the sun, brown dwarfs within 26 light-years from the sun are circled, with objects in blue having been previously identified, while red circles indicate new brown dwarfs revealed by WISE.
In the early 1980s, scientists noticed that extinctions on Earth seemed to fall in a cyclical pattern, and the long timespan caused them to turn to astronomical events for an explanation.
In 1984, Richard Muller of the University of California Berkley suggested that a red dwarf star 1.5 light-years away could be the cause of the mass extinctions. Later theories have suggested that Nemesis could be a brown or white dwarf, or a low-mass star only a few times as massive as Jupiter. All would cast dim light, making them difficult to spot.
Scientists think that Nemesis affects the Oort cloud, which surrounds the Sun beyond the range of Pluto. Many of its ‘chunks’ travel around the Sun in a long-term, elliptical orbit. As they draw closer to the star, their ice begins to melt and stream behind them, making them recognizable as comets. If Nemesis travelled through the Oort cloud regularly, some argue, it could ‘kick’ extra comets out of the sphere and send them hurling toward the inner solar system — and Earth. Impact rates would increase, and mass extinctions would be more common.
The Kuiper Belt, a disk of debris that lies inside of the solar system, also has a well-defined outer edge that could be sheared off by a companion star. Researchers have found other systems where a companion star seems to have affected the shape of the debris disks.
The dwarf planet Sedna lends further credence to the existence of a companion star for the Sun. With an orbit of up to 12,000 years, the planet presents a puzzle to many. Scientists have suggested that a massive object such as a dim star could be responsible for keeping Sedna so far from the Sun.