An "
Alien"
asteroid from another star system has been discovered sharing
Jupiter's orbit.
Through a telescope the asteroid look like every other in the solar system save for one crucial difference - it is travelling in the wrong direction.
It is the first time an interstellar space rock has been found to be permanently residing in the solar system.
Earlier this year, a tumbling cigar-shaped object named 'Oumuamua', hit the headlines after flying into earth's galactic backyard, but it merely passed through and out again.
But the new 1.8 mile wide rock - code-named 2015 BZ509 - appears to be a long-term resident, according to a study in the journal Monthly Notices of the Royal Astronomical Society.
The first clue that it was not a native of the solar system came from its "retrograde" orbit of the sun, the opposite the direction of travel taken by all the planets and almost every other object in our system.
Dr Fathi Namouni, from the Cote d'Azur Observatory in France, lead author of the study, said: "How the asteroid came to move in this way while sharing Jupiter's orbit has until now been a mystery.
"If 2015 BZ509 were a native of our system, it should have had the same original direction as all of the other planets and asteroids, inherited from the cloud of gas and dust that formed them."
Scientists have concluded it survived by orbiting the sun exactly in step with Jupiter, but in the opposite direction.
Co-author Dr Helena Morais, from the Estadual Paulista University in Brazil, said: "The close proximity of the stars, aided by the gravitational forces of the planets, help these systems attract, remove, and capture asteroids from one another."
Computer simulations suggest that the asteroid made the jump to our solar system 4.5 billion years ago when the sun was part of a tightly packed star cluster.
“That was completely unexpected...it means it is an alien to the solar system,” said Dr Namouni.
Since asteroids and comets carry organic chemicals and water, the discovery could shed light on the origins of life on Earth, the scientists believe.