Since its release on Netflix, Adam McKay’s film has been praised by scientists. Can we really imagine a comet crashing on Earth one day?
Prophetic movie? Perfect metaphor on climate change, Don’t Look Up has caused a sensation since its release on Netflix. With us, it is 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 headed straight for Earth! And this, in the next six months…
Threats from above
As the film reveals, NASA does have a planetary defense coordination office, the OFSP. Its mission is to scan the skies to discover and catalog potentially dangerous space rocks long before they reach Earth; and to 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 amazing speeds, up to 70km/s. They are not easily visible until they approach Jupiter’s orbit where the sun’s energy ignites them and gives them their characteristic tail. Depending on their size, the 6 months evoked in the film are quite believable.
Asteroids represent a less significant threat because they move more slowly. Discovered today, an asteroid could 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 we know where they all are“, explains Lindley Johnson, planetary defense officer of NASA, to 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 technologies.“
In 2013, an asteroid 20m in diameter exploded in the sky above 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 however causing any casualties. The asteroids that concern the PDCO the most – and get the majority of their attention – are those measuring 140 meters or more.
“140 meters is the threshold that can cause a lot of damage“, explains 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? It’s a whole different matter. No one is going to enjoy exploiting it – this part of the plot is purely whimsical. Even less if it is a comet, which would leave not decades but only a few months to prepare.
Destroying it with explosives, even nuclear, is not excluded if the delay is really short and if the object is huge. But that would cause another problem because the giant boulder would not be destroyed but rather scattered into a large number of smaller boulders.
“It’s hard to predict where all these pieces are going“, explains Lindley Johnson, “and it is difficult to ensure that it will have been broken into pieces small enough for the Earth’s atmosphere to cope with.“
Asteroids that give us more time to act could be deflected rather than destroyed, slowing them down or altering their trajectory just enough to pass Earth.
On November 24, 2021, NASA launched the spacecraft Double Asteroid Redirect 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 rock that circles the sun on a trajectory that takes it from outside Earth’s orbit to outside Earth’s orbit. the orbit of Mars.
Didymos itself has a small orbiting moon, 160 meters in diameter, named Dimorphos. As it approaches Didymos, the DART will deliberately crash into Dimorphos, and scientists will then determine how much the speed and direction of its orbit will have 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 that, unlike Didymos, could actually pose a risk to us, NASA also plans 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 is perfect. All of them, however, could prove useful.