spaceSpace and Physics

Scientists Have Confirmed We Had Our First Ever Insterstellar Visitor Last Month


Jonathan O'Callaghan

Senior Staff Writer

An artist's impression of what 'Oumuamua might look like. ESO/M. Kornmesser

Astronomers have released the first results from an in-depth study on the suspected interstellar object that flew into our Solar System last month – and the findings are fascinating.

The object is known as 1I/2017 U1 (`Oumuamua), a Hawaiian name that means “reach out for” (‘ou) and “first, in advance of” (muamua). The letter “I” denotes that this is our first ever recorded interstellar visitor, confirmed by this study.


Published in Nature, the results show that the object is a bizarre elongated shape, measuring 10 times as long as it is wide. Its length is thought to be at least 400 meters (1,300 feet) long. It spins on its axis once every 7.3 hours, with a large variation in brightness revealing its odd shape.

The observations also confirmed this object – now certain to be an asteroid rather than a comet, as it had no visible coma – was dark and reddish in color. This was the result of cosmic rays blasting it for the millions of years it has been traveling through space, irradiating its surface.

It also appears to be dense, meaning it is possibly rocky or has a high metallic content, and lacks any significant water ice.

"What we found was a rapidly rotating object, at least the size of a football field, that changed in brightness quite dramatically," Karen Meech from University of Hawaii's Institute for Astronomy (IfA), the study’s lead author, said in a statement. "This change in brightness hints that `Oumuamua could be more than 10 times longer than it is wide – something which has never been seen in our own Solar System."

'Oumuamua's path into our Solar System. ESO/K. Meech et al.

The object was first spotted on October 19, 2017, by the Pan-STARRS 1 telescope in Hawaii. It had made its journey around the Sun and was heading out of the Solar System, so astronomers raced to get as much data as possible.

And race they did. Using a variety of observatories, including the European Southern Observatory’s (ESO) powerful Very Large Telescope (VLT) in Chile, they were able to work out its size, color, shape, and more.

“We had to act quickly,” team member Olivier Hainaut from ESO in Garching, Germany said in the statement. “`Oumuamua had already passed its closest point to the Sun and was heading back into interstellar space.”

Now, astronomers are continuing to observe the object in the hope of getting even more data, including where it came from. There have been some suggestions so far, including a star cluster about 200 light-years away, but we don't know for sure. If it's like asteroids in our Solar System, though, it could have been born in a planetary system just like ours.


At least one interstellar object is thought to pass into our Solar System every year, but they're hard to spot, which is why this is the first. It's hoped that upcoming telescopes like the Large Synoptic Survey Telescope (LSST) could find more in the feature.

And that, well, is just freaking awesome. A tiny rock from another planetary system made its way here, waved, and headed off to space. Farewell, interstellar traveller.

A composite image of `Oumuamua, which is the white dot in the middle. ESO/K. Meech et al.


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