An artist’s impression of what the first interstellar asteroid may look like ESO/M. Kornmesser

Scientists now know what that interstellar visitor — the asteroid that recently zipped through our solar system from outer space — might look like. And it’s an oddity.

Immediately after ‘Oumuamua’s discovery early this November, telescopes around the world were called into action to study the object more closely. They had to be speedy, given that the object is currently moving 95,000 kilometres per hour and heading away from the sun. Though it is rapidly fading, they were able to make a few key notes on its appearance.

The first observation — and the first clue that ‘Oumuamua was an oddity — was its brightness. It brightened and dimmed dramatically by a factor of 10 every 7.3 hours. This suggested that the object was likely highly elongated. Scientists know now that ‘Oumuamua is roughly cigar-shaped at 400 metres long and perhaps 10 times smaller in width.


That aspect ratio is greater than any asteroid or comet observed in the solar system and may provide new clues into how other planetary systems form.

Though the asteroid’s shape does make it appear truly alien, its colour — a dark red hue — is more familiar. Like the objects in the outer solar system, scientists suspect that this is because the object lacks a lot of water or ice, and it has been darkened and reddened by the impact of cosmic rays over millions of years.

Astronomers will continue to make observations of the object before it slips back into darkness. Any further studies will be key given that interstellar asteroids are faint and hard to spot despite the fact that they likely pass through the inner solar system about once a year.

Journal reference: Nature, DOI: 10.1038/nature25020