It’s not long now before we find out for sure whether Comet 3I/ATLAS is actually an intergalactic Trojan Horse sent to release tiny probes as it hides behind the Sun.
This highly unlikely theory has nevertheless been put forward by a controversial astrophysicist, and to be fair, at least it has focused attention on a fascinating object visiting us from another star system.
What is 3l/ATLAS and how big is it?
Dr Mark Norris, of Lancashire University, told Metro that there is no reason to think the interstellar comet has a technological origin, and it’s a shame that the idea has had so much traction, because it’s interesting enough as it is.
He recently gave a presentation on the first 100 days since we spotted it in July, captioned: ‘Spoiler: It’s not Aliens’.
But if it’s not, what is it?
Dr Norris told Metro: ‘It’s something that’s drifted through space, probably for longer than our solar system has existed.’
He said that if it behaves differently to comets we usually observe, this is to be expected as its chemical composition would be very different, formed when our galaxy was much younger, with fewer supernovas exploding and spewing out elements.
Dr Loeb has cited the comet’s nickel emissions without iron, saying they resemble those found in industrially produced alloys, and also pointed to its ‘anti-tail’ where its trail of dust pointed towards the Sun rather than away from it, then switched which he said could show ‘braking thrust’.
But Dr Norris said: ‘There’s nothing about this thing that makes anyone who understands comets or the solar system concerned.’
To recap, 3I/ATLAS is only the third space rock ever identified as coming from outside our solar system.
After it was identified aroud four months ago, it has zoomed through our neighbourhood in a ‘hyperbolic orbit’ which means it’s going so fast it won’t be captured by the Sun’s gravity, and will head back out to drift in outer space for potentially billions more years.
It is bigger than the previous two interstellar comets we’ve spotted, 1I/Oumuamua (found in 2017) and 2I/Borisov (found in 2019).
But it’s difficult to say exactly how big, because ‘it’s quite an active comet, throwing out a lot of material,’ Dr Norris said. ‘So you’ve got this coma of dust and gas surrounding the nucleus; all we can see is the sort of cloud.’
From what we can tell, it’s potentially up to 5km across, though probably more in the region of 2km, compared to 100m Oumuamua and 400m Borisov.
There have been plenty of bigger solar system comets, but we still ‘certainly wouldn’t want it to hit us, but it’s not going to,’ Dr Norris said.
Right now, it’s in a blind spot from Earth because it’s behind the Sun, and much too bright for us to see.
But from around November 2, the European Space Agency’s JUICE spacecraft is set to train instruments on it from the far side of the Sun, so we can get the latest on what it’s up to.
‘Maximum speed’
3I/ATLAS has just reached perihelion, its closest point to the Sun, where gravity helped it reach its maximum speed.
It will slow down a bit now, but still move very rapidly.
‘When we first detected it, it was around 60 kilometres per second, which is about twice as fast as the Earth goes around the Sun.
‘By the time it leaves our solar system entirely, it’ll still be going at 58 kilometres per second.’
Where did it come from and where is it going?
We don’t know for sure where it came from, but it wasn’t anywhere near ourown solar system.
Scientists trying to figure out its origin using Gaia mapping of stars in the Milky Way don’t think it has had close passage with any other star ‘in at least 10 million years up to this point,’ Dr Norris said.
‘It’s potentially going to wander again for billions more years before it interacts with another star system.’
We don’t know exactly when it will leave our solar system, but it will be within ten years, and will disappear from being close enough to observe from mid 2026.
‘Can we grab a bit of one?’
Such an unusual object could give us insights about what other parts of the universe look like, and reveal whether our own solar system is typical or not.
There’s no way we can catch up to 3I/ATLAS, but Dr Norris said that we might be able to intercept something similar in future.
As we get better at tracking, we’ll likely spot more interstellar comets.
He asked: ‘Is there a way we can actually grab a bit of one? Can we bring a bit back and actually physically see what what another star system is made from?’
This could happen within ten years, he thinks.
There is already a mission being planned called Comet Interceptor, which will wait out in the solar system for a suitable comet.
‘They’ve said if an interstellar one appears and it’s in the right part of the sky, then they they would go for it as well,’ Dr Norris said.
Should we be worried about 3I/ATLAS?
Probably not: even Dr Loeb has said it’s unlikely it has an unnatural origin, but he thinks it’s important to consider the possibility of a highly destructive ‘black swan’ event.
Dr Norris acknowledged that if it was dangerous, it could be ‘very bad’, but added:’The fact is, there are an awful lot of very good planetary scientists, people, who study comets, who are looking at this and working together, and they’re not concerned by it. So why would you do anything?
‘You know, if after November 2, when we start tracking it again, it’s doing something unusual, then fine. But there’s no reason to be concerned now.’
So, we should find out more in four days…
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