“Don’t Look Up”: What would happen if a comet swooped down on Earth?

Many feature films have had fun imagining what could happen to the Earth and its inhabitants if a asteroid or a comet had hit the planet. The general public was able to savor the outrageous heroism of Bruce Willis in Armageddon or the excessive special effects of a Deep Impact. The film Don’t Look Up, released on netflix on December 24, 2021, starts from a similar postulate: two astronomers, played by Jennifer Lawrence and Leonardo DiCaprio, discover a comet heading for Earth. Scientists quickly find themselves confronted with the disinterest of the media and the inaction of the government, while the Earth is about to be destroyed. But the script of the film, which takes on an aura of seriousness in its treatment of the cosmic menace, is it believable?

A big story

In Don’t Look Up, doctoral student Kate Dibiasky discovers a comet about 10 kilometers wide, realizing a few hours later that it threatens the Earth, on which it will crash six months later. The comet, referred to by scientists as a “planet killer”, reaches the Pacific Ocean, causing an unprecedented cataclysm and the almost immediate extinction of animal and plant life.

In space, there are indeed different types of bodies and celestial objects that could be a threat. NASA Center for Near-Earth Object Studies (Center for Near Earth Objects Studies), in charge of monitoring objects and asteroids gravitating in a perimeter relatively close to the Earth, has thus identified nearly 27,000 asteroids.

Only 2,000 of them are considered potentially dangerous, and 158 have a size equivalent to or greater than one kilometer in diameter. Among these asteroids, some have acquired a great reputation among followers of apocalyptic theories. Apophis and its 350 meters in diameter and the most imposing Benu, measuring 500 meters in diameter, come up annually in predictions of the end of the world.

Some comets can have sizes similar to the most massive asteroids, only their compositions allow to differentiate the two types of celestial objects. Some comets, however, reach disproportionate dimensions, sometimes much more impressive than the comet Dibiasky of Don’t Look Up. C/2014 A₂₇₁, Where Bernardinelli-Bernstein, imaged for the first time in 2014, could thus have a diameter of nearly 100 kilometers. For comparison, the diameter of Bernardinelli-Bernstein would include that of Ile-de-France!

Planet killers?

Can we seriously consider that such objects destroy the Planet and all forms of life on its surface? One simulator, created by researchers from theImperial College of London and the University of Purdue, demonstrates that an object 10 kilometers in diameter crashing at 51 meters per second on Earth would cause considerable material damage. The impact of such a comet in the center of Paris would scorch the majority of the soil on the entirety of French territory, burning to the third degree an observer located more than 700 kilometers away, while in Toulouse, the theoretical maximum force of the blast would be 725 meters per second. At the point of impact, everything would be obliterated in an area 300 kilometers in diameter, with a earthquake with a magnitude of 10.4 on theRichter scale.

David Morrison, astronomer working for theAmes Research Center of NASA, explained in 1999 to the magazine Scientific American that the impact of a massive body of 10 kilometers, with a power of 100 million megatons, could cause a mass extinction. In addition to the violence of the impact and the immediate effects mentioned above, the collision would release a vast pile of dust and materials which would permanently obscure theatmosphere earthly. It was a similar event that accelerated the disappearance of the dinosaurs, 66 million years ago.

But, for now, no comets or asteroids directly threaten the Earth. NASA and other space agencies keep the planet safe with tools like the Sentry program. Deflection programs for objects close to the Earth are under study. In November 2021, NASA launched the dart mission which will test the deflection capabilities of an asteroid using a probe in September 2022.