It sounds like the start of a cheesy science-fiction film. A gigantic, ancient, icy… thing spotted hurtling towards us by a lonely astronomer.
But this is exactly what happened for stargazers following the discovery of a weird interstellar object called 3I/ATLAS, or ‘third interstellar’, this month.
The object is big – possibly as wide 12 miles, larger than the asteroid that wiped out the dinosaurs – and is speeding towards us at 130,000mph.
3I/Atlas was spotted on July 1 by the NASA-funded ATLAS survey telescope in Río Hurtado, Chile, when it was 420million miles away.
After being given the catchy name, ‘A11pl3Z’, scientists soon realised that the object came from interstellar space.
As you read this, 3I/ATLAS is about 416million miles away from the Sun and travelling from the direction of the constellation Sagittarius.
This is only the third time that astronomers have found an uninvited guest in our solar system.
First was Oumuamua, a Manhattan-sized, cigar-shaped rock that passed close to us in 2017. For a time, one astronomer suspected it was an alien spaceship.
Then, in 2019, the comet Borisov paid us a drive-by visit.
Dr Alfredo Carpineti, an astrophysicist living in London, told Metro that our latest ‘interstellar interloper’ is ‘very exciting’.
‘What makes it very special is that this object is very different compared to the previous two visitors, Oumuamua and Comet Borisov. It’s moving almost twice as fast, for example,’ the senior staff writer for IFLScience said.
Where did 3I/ATLAS come from?
What first gave away that 3I/Atlas is not of our solar system was its eccentric, hyperbolic orbit, meaning it’ll loop around the Sun before being flung back out into space.
By tracing its celestial footsteps, Dr Carpineti said, it shows that it ‘might come from a whole different region of the galaxy compared to the other two’.
‘It might be a lot older, at least 7billion years old,’ he added. ‘Much older than the solar system.’
The trajectory of 3I/ATLAS hints that it came from the Milky Way’s ‘thick disk’ – the retirement home of stars on the outskirts of our galaxy – according to a paper seen by Dr Carpineti for IFLScience.
Researchers say 3I/ATLAS probably formed around an ancient star and is made up of a lot of water ice.
What is it exactly?
Scientists say it is a comet, a giant, dirty snowball. As it soars towards the Sun, the ice will melt and create a wispy tail.
When sunlight bounces off this plume of gas and dust, called a coma, this makes the object appear very bright.
A big clue that 3I/ATLAS is a comet is how bright it is – enough that it’s already visible using modest-sized telescopes. Asteroids, space rubble, have far darker surfaces.
Is there a chance it will hit Earth?
We’ll learn more about what 3I/ATLAS is as it zooms closer and closer to us, Dr Carpineti said.
But don’t worry, it won’t get too close for comfort. ‘This interstellar interloper is a cosmic curiosity and it poses no threat to Earth,’ he added.
‘The closest it will get to the Sun is 210million kilometres, a little bit closer than Mars,’ which would be around Halloween or early December.
‘At that point, the Earth will be on the other side of the Sun, so we won’t even be able to see it at closest approach.’
Get in touch with our news team by emailing us at webnews@metro.co.uk.
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