The data that once suggested the Sun is orbited by a distant dark companion now raises even more questions
Over the last 500 million years or so, life on Earth has been threatened on many occasions; the fossil record is littered with extinction events. What's curious about these events is that they seem to occur with alarming regularity.
Nemesis is a theoretical dwarf star thought to be a companion to our sun. The theory was postulated to explain a perceived cycle of mass extinctions in Earth's history. Scientists speculated that such a star could affect the orbit of objects in the far outer solar system, sending them on a collision course with Earth.
In the early 1980s, scientists noticed that extinctions on Earth seemed to fall in a cyclical pattern. Mass extinctions seem to occur more frequently in the last 27 million years. The long span of time 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 speculated that Nemesis may affect the Oort cloud, which is made up of icy rocks surrounding the sun beyond the range of Pluto. Many of these 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 traveled through the Oort cloud 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 in the eyes of some 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.
Nemesis Star Theory: The Sun's 'Death Star' Companion