An asteroid collides with Earth.
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About 66 million years ago, a “planet killer” – a 10-kilometer-wide rocky asteroid – hit Earth. The Chicxulub impact caused a mass extinction on a planetary scale, killing off an estimated 76 percent of all species living on Earth at the time, including the dinosaurs. According to a study published by Philip Lubin and Alexander N. Cohen, both physicists at the University of California in Santa Barbara, there is a chance that humanity could survive such a similar impact happening in the near future.
There currently are about 1,200 asteroids on a publicly available asteroid risk list, but all are smaller than one kilometer. The probability of a Chicxulub sized asteroid (5 to 15 kilometers across) hitting Earth is once in a billion years – very low, but not impossible.
There are three possible ways to deal with the potential threat as analyzed in the study.
First, and the most optimistic scenario, is to prevent the impact by destroying the asteroid or changing its trajectory in time. Already today, scientists are searching for asteroids that may cross Earth’s path, and discussing possible defense strategies. Nuclear bombs could pulverize parts of the asteroid, forming smaller chunks that will miss Earth entirely or burn up in the terrestrial atmosphere. For asteroids about the size of one kilometer, rockets and the yield of modern nuclear weapons are already advanced enough to successfully intercept the celestial body and destroy it completely. Larger asteroids must be split into smaller fragments from the inside. Maybe an automated rover, like active on Mars today, could be used to drill a borehole and place explosives beneath the surface. But for a very large asteroid, larger than 10 kilometers, it would require a 10 million gigatons explosion to do any real damage. The most powerful nuclear device ever detonated by humans was a mere 50-megatons bomb.
If the impact is unavoidable, the second scenario involves large underground bunkers to survive the impact and its aftermath. Bunkers could be constructed in cratons, the thick and stable cores of continents, or deep beneath the oceans. They could be used to store goods necessary to survive the first years after the impact, like food, medicine, fuel and fresh water. They could also act as a genebanks, like the Global Seed Vault in the tectonically stable and remote Arctic Svalbard archipelago.
Based on computer simulation, in the first moments of the impact, the energy released by the collision will cause a firestorm, igniting large areas of the Earth’s surface. The soot of the mega-fires burning on entire continents, together with dust and water vapor, will form a thick blanket of clouds in Earth’s upper atmosphere, significantly reducing the sunlight reaching the surface. Temperatures would drop for decades, reducing the growing season of plants. A “Nuclear Winter” with widespread famine in an already struggling world would be the consequences.
The last scenario, lampooned in the successful Netflix movie Don’t Look Up, is to ignore the problem until it is too late. The authors conclude that “in any realistic scenario of an existential threat, presumably logic would prevail, at least one would hope.”
