The first known interstellar object to travel through our solar system got an unexpected boost in speed and shift in trajectory as it passed through the inner solar system last year.
The cigar-shaped object, named ‘Oumuamua, was spotted by the Haleakala observatory in Hawaii on October 19 last year.
Its appearance and behaviour baffled scientists and led to speculation that it might even be an alien artefact – and now they have found it got a strange speed boost while passing through.
‘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,’ said Marco Micheli of ESA’s (European Space Agency) Space Situational Awareness Near-Earth Object Coordination Centre in Frascati, Italy, and lead author of a paper describing the team’s findings.
The speed boost was consistent with the behavior of a comet, said co-author Davide Farnocchia of the Center for Near Earth Object Studies (CNEOS) at NASA’s Jet Propulsion Laboratory (JPL).
This illustration shows ‘Oumuamua racing toward the outskirts of our solar system. As the complex rotation of the object makes it difficult to determine the exact shape, there are many models of what it could look like.
‘This additional subtle force on ′Oumuamua likely is caused by jets of gaseous material expelled from its surface,’ said Farnocchia.
‘This same kind of outgassing affects the motion of many comets in our solar system.’
Comets normally eject large amounts of dust and gas when warmed by the Sun.
But according to team scientist Olivier Hainaut of the European Southern Observatory, ‘there were no visible signs of outgassing from ′Oumuamua, so these forces were not expected.’
A cigar-shaped object that recently passed close to Earth has been confirmed as the first object object from outside the Milky Way to visit the solar system. The Oumuamua asteroid (artist’s impression) floated through our star system in November
The team estimates that ′Oumuamua’s outgassing may have produced a very small amount of dust particles – enough to give the object a little kick in speed, but not enough to be detected.
Karen Meech, an astronomer at the University of Hawaii’s Institute of Astronomy and co-author of the study, speculated that small dust grains, present on the surface of most comets, eroded away during ′Oumuamua’s long journey through interstellar space.
‘The more we study ′Oumuamua, the more exciting it gets,’ Meech said.
‘I’m amazed at how much we have learned from a short, intense observing campaign. I can hardly wait for the next interstellar object!’
′Oumuamua, less than half a mile in length, now is farther away from our Sun than Jupiter and traveling away from the Sun at about 70,000 mph as it heads toward the outskirts of the solar system.
In only another four years, it will pass Neptune’s orbit on its way back into interstellar space.
Because ′Oumuamua is the first interstellar object ever observed in our solar system, researchers caution that it’s difficult to draw general conclusions about this newly-discovered class of celestial bodies.
However, observations point to the possibility that other star systems regularly eject small comet-like objects and there should be more of them drifting among the stars.
Future ground- and space-based surveys could detect more of these interstellar vagabonds, providing a larger sample for scientists to analyze.
WHAT IS ‘OUMUAMUA AND WHAT DO WE KNOW ABOUT IT?
A cigar-shaped asteroid named ‘Oumuamua sailed past Earth at 97,200mph (156,428km/h) in October.
It was first spotted by a telescope in Hawaii on 19 October, and was observed 34 separate times in the following week.
It is named after the Hawaiian term for ‘scout’ or ‘messenger’ and passed the Earth at about 85 times the distance to the moon.
It was the first interstellar object seen in the solar system, and it baffled astronomers.
Initially, it was thought the object could be a comet.
However, it displays none of the classic behaviour expected of comets, such as a dusty, water-ice particle tail.
The asteroid is up to one-quarter mile (400 meters) long and highly-elongated – perhaps 10 times as long as it is wide.
That aspect ratio is greater than that of any asteroid or asteroid observed in our solar system to date.
But the asteroid’s slightly red hue — specifically pale pink — and varying brightness are remarkably similar to objects in our own solar system.
Around the size of the Gherkin skyscraper in London, some astronomers were convinced it was piloted by aliens due to the vast distance the object traveled without being destroyed – and the closeness of its journey past the Earth.
Alien hunters at SETI – the Search for Extra-terrestrial Intelligence based at Berkeley University, California said there was a possibility the rock was ‘an alien artefact’.
But scientists from Queen’s University Belfast took a good look at the object and said it appears to be an asteroid, or ‘planetesimal’ as originally thought.
Researchers believe the cigar-shaped asteroid had a ‘violent past’, after looking at the light bouncing off its surface.
They aren’t exactly sure when the violent collision took place, but they believe the lonely asteroid’s tumbling will continue for at least a billion years.