US scientists who have studied patterns in cometary orbits believe a distant body that may be a tiny sister star of the Sun could exist in the far reaches of the solar system.
British research announced last week had reached similar conclusions, though it suggested such a body was most probably a planet.
Research unveiled at the American Astronomical Society's planetary sciences meeting by John Matese, professor of physics at the University of Louisiana at Lafayette, and colleagues suggests it may, in fact, be a brown dwarf, a sort of failed star. It would bring the Sun more into line with its neighbours - scientists believe multiple-star systems are very common in the galaxy and a survey of 123 nearby sunlike stars found more than half had one or more companions.
Professor Matese's work involved the study of the orbits of 82 comets that originated in the Oort Cloud, a vast shell of debris that surrounds the solar system and from which most comets come.
They found a pattern connecting the orientation and shape of the path each comet took, which they felt was best explained if they had been influenced by the gravitational pull of an object three times the size of Jupiter and existing about 25,000 times farther from the Sun than the Earth.
"This object would be called a brown dwarf and not a planet since, if it exists, it would not have formed from the disc of material that surrounded our forming Sun as the planets did," said Professor Matese.
"As more Jovian-mass companions are found around other stars, sometimes several of them in the same system, it becomes more reasonable to consider the possibility of a wide binary companion to our Sun." Jupiter is much the biggest object in the solar system apart from the Sun and is about 300 times the size of the Earth.
Scientists have previously speculated on the existence of a companion star to the Sun, dubbed Nemesis, that caused periodic storms of comets to flood the inner solar system, responsible for planetary collisions and mass extinction events on Earth.
This theory has been widely discredited. The new theory gives the brown dwarf a far milder effect, nudging some comets into an inward course but by and large not having any great impact on the planets. While the star would be so dim as to have escaped detection by optical telescopes, its heat emissions should make it observable by the next generation of infrared telescopes.
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