Scientists investigating a cigar-shaped interstellar object spotted almost two years ago have ruled out theories that it was an alien spaceship - but admit they still don’t know how to classify the vast chunk of rock.
The unusual object has been named ‘Oumuamua (pronounced oh-MOO-uh-MOO-uh) - Hawaiian for a messenger arriving from a great distance - and is estimated to be half a mile (800m) long.
And as the first object from another star system recorded passing through our solar system, it has triggered a great deal of interest.
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So when was it first spotted?
Scientists tracked the reddish-coloured object from 14 October 2017 until 2 January 2018, after it was first sighted by astronomers at the University of Hawaii using a Pan-STARRS1 telescope, reports Reuters.
‘Oumuamua then became too faint to detect even using the most powerful telescopes.
What is it?
Astronomers are still uncertain about that.
“Our key finding is that ‘Oumuamua’s properties are consistent with a natural origin,” says University of Maryland astronomer Matthew Knight, author of a new research paper published in the journal Nature Astronomy. “We have tried to avoid putting it in one of those boxes and prefer to call it more generically an ‘object’.”
Experts have suggested that ‘Oumuamua might be a comet, an asteroid or a chunk of planet, but have been unable to explain its strange shape and spin, which did not follow the expected gravitational orbit.
“A paper last year from Harvard astrophysics enfant terrible Avi Loeb briefly suggested the possibility that the rock was an alien probe. It was like a spark to dry tinder, honestly, and other scientists have been running around with buckets ever since,” reports Science Alert.
Knight insists that the evidence shows the “alien explanation is unwarranted”.
Are there more out there?
“We have never seen anything like ‘Oumuamua in our solar system,” said Knight. “It’s really a mystery still... There is a whole host of natural phenomena that could explain it.”
But as Space.com notes, “astronomers anticipate spotting more interstellar visitors” as telescope technology increases.
“The Large Synoptic Survey Telescope (LSST), currently under construction in Chile, may help to reveal many of these once the instrument sees first light in 2022,” reports the specialist news site.
Knight says that until more interstellar objects are detected, there is no way of knowing whether Oumuamua is “weird or common”.
“If we find ten to 20 of these things and ‘Oumuamua still looks unusual, we’ll have to re-examine our explanations,” he concludes.
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