Mysterious cigar-shaped interstellar asteroid experienced violent past, reveals new study

'Oumuamua - the first known interstellar object to visit our solar system - has experienced a violent past, causing it to tumble around chaotically for many billions of years, a study suggests The object flew through our solar system in October and was originally thought to be a comet, then it was later revealed as a cigar-shaped asteroid. Since October, researchers at the Queen's University Belfast have been analysing the brightness measurements of the object. 

They discovered that 'Oumuamua was not spinning periodically like most of the small asteroids and bodies that we see in our solar system. Instead, it is tumbling, or spinning chaotically, and could have been for many billions of years. While it is difficult to pinpoint the exact reason for this, it is thought that 'Oumuamua impacted with another asteroid before it was fiercely thrown out of its system and into interstellar space. 

"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 Wes Fraser, Queen's University Belfast in the UK. "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," said Fraser. Until now, scientists had been puzzled that 'Oumuamua's colour varied between measurements.

However, the research has now revealed that its surface is spotty and that when the long face of the cucumber-shaped object was facing telescopes on Earth it was largely red but the rest of the body was neutral coloured, like dirty snow. "Most of the surface reflects neutrally but one of its long faces has a large red region. This argues for broad compositional variations, which is unusual for such a small body," said Fraser.

The findings, published in the journal Nature Astronomy, have helped to build a more accurate profile of 'Oumuamua. "We now know that beyond its unusual elongated shape, this space cucumber had origins around another star, has had a violent past, and tumbles chaotically because of it," Fraser said. "Our results are really helping to paint a more complete picture of this strange interstellar interloper. It is quite unusual compared to most asteroids and comets we see in our own solar system," he said.