Don’t Look Up: Can a Comet Really Crash on Earth?

Since its release on Netflix, Adam McKay’s film has been praised by scientists. Can we really imagine that a comet will one day crash on Earth?

Prophetic film? A perfect metaphor for climate change, Don’t Look Up has been causing a stir since its release on Netflix. With us, it’s Cyril Dion who is full of praise for the message of the film. But is the story plausible? As a reminder, a comet 9km in diameter is discovered by the young doctoral student Kate Dibiasky, played by Jennifer Lawrence.

But according to the studies of his supervisor, Dr. Randall Mindy played by Leonardo DiCaprio, we realize that this comet is about the same size as the one that wiped out the dinosaurs 65 million years ago and that ‘she’s heading straight for Earth! And this, in the next six months …

Threats from the sky

As the film reveals, NASA does have a planetary defense coordination office, PDCO. Its mission is to scan the skies to discover and catalog potentially dangerous space rocks long before they reach Earth; and help the government coordinate a response by either deflecting or destroying the object.

In the case of comets, there would be little time to react. Comets can reach breathtaking speeds of up to 70km / s. They are not easily visible, until they approach the orbit of Jupiter where the energy of the sun ignites them and gives them their characteristic tail. Depending on their size, the 6 months mentioned in the film are quite credible.

Don't look up: can a comet really crash on earth?
NIKO TAVERNISE / NETFLIX

Asteroids are less of a threat because they move more slowly. Discovered today, an asteroid may not cross Earth’s orbit – and therefore threaten it – for a century.

Our strategy is to find the population of objects of significant size, so that we know where they are all located.“Lindley Johnson, NASA’s planetary defense officer, told the magazine Time. He reviewed a draft script for Don’t Look Up over two years ago. “Once we do that, it will give us decades of head start and we will have time to use all available technology.

In 2013, an asteroid 20m in diameter exploded in the sky over Russia. Its entry into the atmosphere destroyed the rock before it reached the ground. The explosion still damaged 7,200 buildings and injured around 1,500 people, without causing any casualties. The asteroids that concern OFSP the most – and capture the majority of their attention – are those that are 140 meters or more in length.

140 meters is the threshold that can cause a lot of damage“says Amy Mainzer, professor of planetary science at the University of Arizona and consultant on the film. But it’s not just the size that makes a space object a threat. It’s also its location. The closer the object, the more disturbing it is.

How to protect the Earth

What if an asteroid or comet of sufficient size rushes towards our planet? This is a whole different matter. No one is going to have fun exploiting it – this part of the plot is pure fantasy. Even less if it is a comet, which would not leave decades but only a few months to prepare.

Destroying it with explosives, even nuclear ones, is not excluded if the deadline is really short and if the object is enormous. But that would pose another problem as the giant boulder would not be destroyed but rather scattered in a large number of smaller boulders.

Don't look up: can a comet really crash on earth?
NIKO TAVERNISE / NETFLIX

It’s hard to predict where all these pieces are going“says Lindley Johnson,”and it is difficult to ensure that it will have been smashed into pieces small enough for the Earth’s atmosphere to cope with.

Asteroids, which give us more time to act, could be deflected rather than destroyed, slowing them down or altering their trajectory just enough to pass the Earth.

On November 24, 2021, NASA launched the spacecraft Double Asteroid Redirection Test (DART) who will try to prove that this concept works. Its target is the asteroid Didymos (which poses no threat to Earth), a 780-meter boulder that circles the sun on a path that takes it from outside Earth’s orbit outside of the orbit of Mars.

Didymos itself has a small orbiting moon, 160 meters in diameter, named Dimorphos. As Didymos approaches, the DART will deliberately crash into Dimorphos, and scientists will then determine how much the speed and direction of its orbit has changed around its parent body.

This is a small test on a small rock and it doesn’t mean Earth is about to have a robust planetary defense system in place, but it is an important first step. To find asteroids which, unlike Didymos, could actually pose a risk to us, NASA is also planning to launch the spacecraft. Near Earth Object Surveyor who will leave in 2026 to scan the skies of our planetary neighborhood in search of anything suspicious.

None of these solutions are perfect. All of them, however, could prove useful.

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