A large lump of interstellar rock was spotted passing through the solar system last year may have been spinning chaotically for many billions of years, according to scientists at Queen's University in Belfast who have been studying 'Oumuamua since it first came into view.

Originally when the elongated cucumber shaped mass passed us by in October, scientists thought it was a comet.

But an international team of researchers, including some at QUB, have since established it is an asteroid.

By studying its brightness, they have also established it is tumbling and spinning and probably has been for billions of years.

QUB scientists Dr Wes Fraser, Dr Pedro Lacerda, Dr Michele Bannister, and Professor Alan Fitzsimmons, are not sure why this is happening.

But they think it may be the result of 'Oumuamua hitting another asteroid and being knocked out of its system into interstellar space and into ours.

"Our modelling of this body suggests the tumbling will last for many billions of years to hundreds of billions of years before internal stresses cause it to rotate normally again," said Dr Fraser.

"While we don’t know the cause of the tumbling, we predict that it was most likely sent tumbling by an impact with another planetesimal in its system, before it was ejected into interstellar space," he added.

The team has also established that 'Oumuamua has a spotty surface, with one long red face and a neutral colour like dirty snow across the rest.

This points to a varying composition, which the researchers say it unusual in such a small body.

The research findings have been published in Nature Astronomy.

"Our results are really helping to paint a more complete picture of this strange interstellar interloper," said Dr Fraser.

"It is quite unusual compared to most asteroids and comets we see in our own solar system."