A mysterious object identified as the first confirmed interstellar asteroid likely came from a binary star system, experts said.
It led to speculation that the vast rock might be an alien spaceship.
But astronomers came to understand that it was an asteroid from interstellar space, which entered the solar system after a journey that may have lasted millions of years.
Now, a new study by scientists from the University of Toronto suggests the entity 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.
Aliens - In pictures
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, the study said.
