Interstellar asteroid came from binary star system
A visitor from outer space identified as the first confirmed interstellar asteroid may have travelled from a binary star system, astronomers believe.
The cigar-shaped object, named 'Oumuamua, was spotted by the Haleakala observatory in Hawaii on October 19 last year.
Its appearance and behaviour baffled scientists and led to speculation that it might even be an alien artefact.
Astronomers now know it was an asteroid, but not one of our own.
'Oumuamua - Hawaiian for "scout" - had entered the solar system from interstellar space after a journey that may have lasted millions of years.
The latest research suggests it was expelled from a binary star system - one with two stars orbiting around each other.
Rocky objects are far more likely to be "kicked out" of their home orbits by binary stars, the scientists found.
In contrast, icy comets, rather than asteroids, were more commonly ejected from lone star systems.
Lead researcher Dr Alan Jackson, from the University of Toronto in Canada, said: "It's remarkable that we've now seen for the first time a physical object from outside our solar system.
"It's really odd that the first object we would see from outside our system would be an asteroid, because a comet would be a lot easier to spot and the solar system ejects many more comets than asteroids."
The research, published in the journal Monthly Notices of the Royal Astronomical Society, suggests that 'Oumuamua originated from a system containing a hot, high mass star.
It may have been cast out some time during the process of planet formation.
When it was discovered, the 400 metre (1,312ft) long object was tumbling and travelling at 30 kilometres per second on a trajectory taking it through and out of the solar system.
At its closest point it passed about 33 million kilometres from Earth.
It appeared to have followed a path roughly in the direction of the star Vega in the southern constellation Lyra.