3I/ATLAS was just a comet – but could we have defended ourselves if it was aliens?

Abraham ‘Avi’ Loeb, a Harvard University astrophysicist, spends most of his waking hours thinking about a giant rock.

The rock’s name isn’t too catchy, 3I/ATLAS, and according to some, it’s more of a cosmic-sized snowball.

But 3I/ATLAS is no ordinary rock – it’s a comet from beyond the solar system which greeted the Earth on December 19.

It’s also an ‘interstellar visitor’ that, if you ask Loeb, could be an alien spacecraft that’s either entirely benign or anything but.

‘In the first case, humanity need not do anything but await the arrival of this interstellar messenger with open arms,’ Loeb tells Metro.

‘It is the second option which is of great concern.’

So, let’s just say that 3I/ATLAS was, in fact, an alien spacecraft. How would we Earthlings react?

What is 3I/ATLAS?

The clump of rock, dust and ice was first spotted in July.

Scientists, star-gazers and even Kim Kardashian have wondered where this comet came from – or if it will hit Earth.

Loeb has pointed out the comet’s chemical makeup, flight path and its size, among other factors, as to why it may be artificial.

Google searches for ‘planetary defence’ have risen by 298% in the last three months.

In a single week of October, the phrase was Googled 147,000 times, according to trend data analysed by Glimps.

Scientists have stressed to Metro that 31/ATLAS poses no threat and that, at its closest, it will come within just 170 million miles of Earth.

Do aliens even know we exist?

Loeb worries that the ‘cat is out of the bag’ for Earth, as humanity has made plenty of attempts to find extraterrestrial intelligence.

In 1977, Voyager 1 and 2 were sent into the abyss of space with discs containing sounds of Earth, recorded greetings and a mix of music.

‘We should be ready for the possibility of a visitor that detected them,’ says Loeb. ‘It may come to save us or destroy us.

‘We’d better be ready for both options and check whether all interstellar objects are rocks.’

The former chair of Harvard’s astronomy department warns that we wouldn’t have long to prepare for an invasion if visitors from another planet were to beeline toward us.

This would be different if life communicated with us beforehand, for example, by sending a slow-moving radio signal.

‘In that case, humanity has plenty of time to contemplate how to respond and or worry about a visit from the transmitting civilisation,’ Loeb says.

‘We need an alien alert system like we do earthquakes’

We have many space observation telescopes on Earth and in orbit, but most aren’t designed to identify spacecraft.

This is why Loeb says Earth needs an international organisation that could decide how we would respond to aliens.

‘It would be prudent to establish an alert system regarding interstellar objects in the spirit of the Richter scale for earthquakes,’ he adds.

‘A natural comet would define the zero point, whereas a clear detection of a spacecraft… would bracket the upper end of the alert scale at a value of 10.

‘Since aliens might not respect the way we split territories on Earth among nations, all humans must cooperate in response to existential threats from space.’

Would our weapons work?

Of course, this is all hypothetical. If life exists beyond Earth, it wouldn’t necessarily be little green men wielding ray guns and cookbooks.

How we could defend ourselves would depend vastly on the ship – is it a sleek, lightweight saucer or a hefty, deep-space mega-cruiser?

Similar thinking goes into asteroids and comets – giant space rocks and space snowballs, respectively – says science journalist Dr Robin Andrews.

The How to Kill An Asteroid author says that for asteroids, we have two options: deflecting them or destroying them.

Smashing space rocks with a probe or blasting them with an ion beam to nudge them off-course is a good option.

‘You ram it pretty hard – just not as hard as you like because you might break it but enough to change its orbit off course,’ he says.

We’d need about 10 years’ advance notice to achieve this, Dr Andrews says, but NASA is always keeping an eye on space rocks.

Another way could be to nuke it, with NASA working on a craft designed that would drill a hole into the rock before pushing the red button.

‘If you try and nuke it and it doesn’t work, then you’ve just created a radioactive asteroid, which isn’t great,’ Dr Robin says.

Though when 3I/ATLAS reached perihelion, the closest it got to the sun, in October, the object reached speeds of 42 miles per second. (That’s the rough equivalent of travelling from east to west London.)

Loeb says Earthly chemical rockets would ‘barely bridge the gap’ of an object travelling at that speed. Even the nuclear-powered rockets engineers are working towards would only hit 34mps.

But Dr Andrews has an even bleaker verdict on whether a comet beelined towards us – it would be a ‘nightmarish scenario’ and, given their sheer size, there’s not much we could do to either deflect or destroy it.

‘The odds of us being hit by a comet are way unfathomably lower than an asteroid,’ he stresses. ‘So even though it would be apocalyptic, the odds of ever having to worry about a comet are near zero. Not zero, but near zero.’

Alien spaceships are in a league of their own, though.

Earth does have a force field that could make a spacecraft landing vulnerable to attack – the atmosphere.

When a spaceship enters the atmosphere, the air beneath it gets so hot that it turns into plasma. This goo can strips the craft and disrupts communication systems.

This would be the perfect time to strike using a Terminal High Altitude Area Defence (THAAD) system, designed to shoot down ballistic missiles.

If somehow our nukes and goo don’t work. What then? Well, Dr Andrews says in terms of planetary defence, our options are limited.

The simple fact that the aliens managed to get to Earth in the first place shows they’re more technologically advanced than us – humans have never even gone past the Moon.

We should just chill, because if they’re hostile, we’re kind of screwed, and if they’re not, then great! But I doubt a nuclear weapon would do anything,’ Dr Andrew says.

‘They’d be stupid enough not to realise what we’re doing with all these rockets coming at them.’

Mark Christopher Lee, a film-maker and UFO expert, tells Metro that the best we can hope for is a ‘War of the Worlds’ outcome, where their alien bodies are no match for the common cold.

‘Just by the fact that they’ve found us means that they’re far more advanced than us, there will probably not much we can do,’ he says.

‘Maybe we could distract them a bit by introducing them to TikTok or other social media platforms.’

Get in touch with our news team by emailing us at webnews@metro.co.uk.

For more stories like this, check our news page.