Our Solar System’s first known interstellar visitor, an object known as ‘Oumuamua, received an unexpected boost in speed last year, leading astronomers to conclude it may be a comet.


The boost occurred as ‘Oumuamua was travelling through the inner Solar System, and could have been caused by jets of gas being expelled from its surface.

Such outgassing is typical of comets.

‘Oumuamua - catalogued as ‘1I/2017 U1’ - is an elongated rocky body that was discovered on 19 October 2017 when the Pan-STARRS 1 telescope in Hawaii detected a faint light in the sky.

It is the first known object to enter our Solar System from interstellar space.

‘Oumuamua is about 800m in length and is currently farther away from the Sun than Jupiter.

It is travelling about 110,000 km per hour and heading towards the outskirts of the Solar System.

A NASA video explaining the science behind the new discovery. Image Credit: NASA’s Goddard Space Flight Center/Katrina Jackson.

"Our high-precision measurements of 'Oumuamua's position revealed that there was something affecting its motion other than the gravitational forces of the Sun and planets," says Marco Micheli of the European Space Agency, a lead author on a new paper describing the findings.

Comets are bodies made up of ice and rock, and often eject gas as they are warmed up by the Sun.

But no such outgassing from 'Oumuamua had been detected.

Now, the team studying ‘Oumuamua believe the outgassing may have produced a small amount of dust particles that gave it a boost in speed, but not enough to be observed.

"The more we study 'Oumuamua, the more exciting it gets," says Karen Meech, an astronomer at the University of Hawaii's Institute of Astronomy and co-author of the study.

"I'm amazed at how much we have learned from a short, intense observing campaign.


I can hardly wait for the next interstellar object!"


Elizabeth Pearson
Ezzy PearsonScience journalist

Ezzy Pearson is the Features Editor of BBC Sky at Night Magazine. Her first book about the history of robotic planetary landers is out now from The History Press.