WARNING: Potential spoilers
It is humanity’s worst nightmare: a comet five kilometres wide will collide with Earth and wipe out almost everything that lives and breathes – including us.
This is the scenario in Netflix’s film Don’t Look Up, where a PhD student played by Jennifer Lawrence and a professor in the form of Leonardo DiCaprio crunch the numbers on a whiteboard and realise we are doomed.
While the Hollywood treatment may make the scenario seem fanciful, a devastating impact that destroys most life on Earth has already happened.
About 65 million years ago an asteroid 10-15km wide crashed into Earth at Chicxulub in Mexico, sending vast amounts of material into the atmosphere and sparking a global winter.
Most life, including the dinosaurs, was destroyed, ushering the era of mammals, which until that time had typically been smaller than rabbits. Another legacy was a crater 100km wide and 30km deep.
Smaller asteroids also pose dangers. For example, hundreds of square miles of forest were destroyed when one about 60 metres wide exploded over Siberia in 1908.
Here we look at the dangers and consider the accuracy of Don’t Look Up.
Would we see it coming six months in advance, as in the film?
In Don’t Look Up, the comet heading for Earth (comets are mostly gas, ice and dust, while asteroids are largely made of rock) was identified six months before it was due to hit.
The comet was modelled on Neowise, which was discovered in late March 2020, just a few months before it made its closest approach to the Sun (and the Earth), which suggests that Don’t Look Up’s timescale was realistic.
While saying that Neowise shows that advance warning of a major comet of just six months is possible, Massimiliano Vasile, a professor of space systems engineering at the University of Strathclyde in Scotland, said such objects would more likely be identified years ahead.
Don’t Look Up’s comet came from the Oort Cloud, the spherical layer of objects surrounding the Sun, and Prof Vasile said two major real-life comets from there (C/2017 K2 and C/2017 T2) were identified five years and two-and-half years respectively before their closest approach to Earth.
“It is unlikely that the size of the comet would be known with such precision as in the movie after the first observation,” said Prof Vasile, who is scientific adviser to the UK delegation of the Space Mission Planning Advisory Group, part of the UN’s Office for Outer Space Affairs.
“The first observation would be followed by many repeated observations from multiple telescopes and involving the whole community.”
Is the threat of a comet or asteroid hitting Earth real?
Monitoring has advanced greatly, said Prof Brad Gibson, director of the E A Milne Centre for Astrophysics at the University of Hull in the UK.
“Two decades ago, only a handful of the potential species-ending kilometre-sized asteroids had been catalogued and their orbits through the solar system carefully measured,” he said.
“As of today, essentially 100 per cent of these extreme asteroids (roughly 1,000 of them) are now covered, and we are in no danger from any of these, at least for several centuries.”
With objects between about 150 metres and a kilometre in size, about half have been catalogued, leaving, Prof Gibson said, “thousands out there that we have yet to discover”.
Typically the undiscovered objects are best observed from the southern hemisphere, where there are fewer monitoring telescopes in operation.
“There are too many blind spots. We need dedicated space-based observatories which can provide us with a 360-degree view of objects potentially targeting the earth,” said Dr Dimitra Atri, a research scientist at the NYU Abu Dhabi Centre for Space Science.
Prof Gibson said over the coming years, as multiple resources come online, 100 per cent monitoring of large (150+ metres) objects will be achieved, and the census of smaller ones – currently “wildly incomplete” – will improve.
Would just a few scientists know?
Don’t Look Up depicts Lawrence and DiCaprio as lone experts who identify the large comet.
Initially, they are told by a sceptical White House not to tell anyone what they know. They eventually go on national television to tell viewers - with mixed results.
In reality, multiple groups identify potential threats and information is shared through established networks, including SMPAG and the International Asteroid Warning Network. Scientific agencies are informed first, then the public.
“It is unlikely that a single person on a white board would calculate the orbit and decide that there is for sure [going to be] an impact,” said Prof Vasile.
Normally, the orbit is initially calculated with a lot of uncertainty and this uncertainty reduces after further observations.
“A decision will be very difficult after the initial observation,” he said. “For the same reason the public will not be informed until there is a much higher degree of certainty … How to communicate this to the public is a very delicate point.”
Could we fire weapons to destroy an asteroid or comet?
There is much interest in deflecting a potentially dangerous asteroid or comet, and an experiment to test out this method began in November when Nasa’s Double Asteroid Redirection Test (Dart) spacecraft was launched on a rocket.
In about nine months’ time Dart’s spacecraft is set to smash into a 170-metre asteroid, Dimorphos, at 15,000mph and scientists will see if the object, which is seven million miles away, has been deflected. Dimorphos is not heading for Earth, so the exercise is about testing the technology.
Scientists have modelled blowing up asteroids using nuclear bombs. Recent findings indicated that with a 100-metre asteroid, a nuclear explosion two months before a projected impact would prevent nearly all fragments from hitting Earth.
However, Prof Vasile said fragmentation carried the threat of creating smaller asteroids that would hit Earth.
“When you fragment the object, you don’t move the shower away from the Earth. You just create a cloud,” he said.
In one million years, Prof Gibson said, a second Sun will pass through our solar system and about 10 million “planet-killing comets will come raining down into the inner solar system”. With current technology, humankind would be powerless to do anything about this.
“If anything is going to wipe us out in an astrophysical sense, that’s the one to watch for,” he said.
Would the public believe the threat?
In an era of fake news, conspiracy theories and widespread anti-vaccine sentiment, it's likely some would simply refuse to believe the reports if there was a threat posed by an object in outer space.
The film's main thrust centres on the battle scientists face to convince decision-makers - including a Donald Trump-style president played by Meryl Streep - of the threats posed by the comet.
Later, our protagonists are horrified as a technology tycoon decides rare minerals on the comet are too valuable to shoot down and that it should be mined even as it hurtles towards Earth.
An entertaining but unsubtle allegory of looming climate change and big business' interests, the film sheds light on what scientist Peter Kalmus, a data scientist at Nasa's Jet Propulsion Laboratory, has said "captures the madness I see every day".