Science

Let's Look Up: An asteroid impact hypothetical

Netflix sensation Don't Look Up reminds us of the danger above our heads, and the cost of ignoring experts.

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Image Credit: NASA

There are few modern filmmakers more adept at blending heartfelt, sobering situations with sharp, satirical humour than Adam McKay. Establishing his post-Anchorman style with 2015’s Oscar-winning financial docudrama The Big Short, wherein Steve Carell’s character’s amusing rage at Wall Street are motivated by a tragic personal loss. McKay leverages the same dichotomy in last December’s disaster-comedy Don’t Look Up.

This time, the motivating apocalypse isn’t human-created, but is in the form of a comet due to impact Earth in six months. Rather, the necessary human-element is provided by our utterly inept and self-interested response in the face of certain annihilation, painting the backdrop for cutting commentaries that are a bit too relevant: social media, fake news, the rise of anti-intellectualism, and our disheartening tendencies towards denial and confrontation and away from coordinated action. The last is a particularly scathing indictment considering the looming climate crisis, and in fact the entire film could be seen as an environmental allegory; characters that remain unmoved by a threat until it’s at their doorstep, at which point any attempt at mitigating action becomes too little, too late.

Despite a nagging defensiveness at being metaphorically chastised for my lack of social activism by celebrities pulling in seven-to-ten figures annually (and the hypocrisy of plutocrats lambasting other plutocrats), I really enjoyed both of these films. However, I’m conscious of the fact that further analysis can be far better handled by Nouse’s stellar film and TV team, and also that this is a science article. So let’s present ourselves a hypothetical: What would actually happen in the event of an impact by a large astronomical object?

The vast majority of space rocks that impact the earth are meteoroids, fragments of rock too small to meet the definition of an asteroid, which can be considered minor planets. Meteoroids enter the Earth’s atmosphere at a speed in excess of 70,000 kilometres per hour, generating an enormous amount of heat and breaking material off the outer surface, which can be observed from the ground as a meteor. Most of us have seen these “shooting stars” at some point, and many still retain enough of their structure to impact the ground as a meteorite – about 6,100 a year or 17 every day. Given that 70 percent of the Earth’s surface is covered by water, and of the 30 percent land left over, only 10 percent can be considered to be inhabited by humans, there’s a 97 percent chance those meteorites are landing somewhere they’ll never be noticed.

Obviously, these relatively tiny rocks have virtually no impact on our daily lives. Once something becomes big enough to actually be noticed by astronomers however, it’s much different. Asteroids and comets (frozen asteroids with the size and chemical compositions to have thin atmospheres, creating a bright tail) would have profound, irreversible and lethal effects on the planet in the event of an impact – and have before.

Anyone with a childhood obsession with dinosaurs [raises hand] has probably heard this story. 66 million years ago, an asteroid roughly ten kilometres wide hit the Earth and caused a mass extinction event that ended the reign of large dinosaurs on Earth. The crater, called Chicxulub, still exists today off the coast of Mexico’s Yucatan peninsula. To give a sense of scale, the Earth was hit at such velocity that the crater is 15-times wider than the asteroid itself. We never see energies like this terrestrially except in the very largest volcano eruptions, and in that case most is released as heat and directed upward rather than as a kinetic blast, which would be far more destructive.

Immediately after impact, anything in the immediate vicinity would be levelled by the initial shockwave. If the asteroid landed in a large body of water, it could cause a megatsunami tens-to-hundreds of metres tall, extending the destruction far beyond the initial blast radius – in Chicxulub’s case, reaching modern-day Texas. The seismic shockwaves radiating out from the blast would trigger global earthquakes and volcano eruptions, releasing toxic gases. The heat produced would effectively broil the Earth’s surface, causing wildfires stretching thousands of miles. But the most damaging and long-lasting ramification would almost certainly be a consequence of the dust and soot produced by the vaporisation of the asteroid and the ground beneath and around it. Along with containing sulfur and other toxic compounds, this natural smog would block out the sun’s light for up to a decade. Perpetual night, as well as the vast temperature swings from the lack of sunlight and greenhouse-effect from enormous CO2 release, would decimate the entire world’s plantlife. Followed in quick succession by ecological collapse.

Despite the brutality of this almost-comically hostile hellscape 66 million years ago, (to quote Jeff Goldblum) life, uh, found a way. The plants hardy enough to survive supported enough food-chains to keep avian dinosaurs and small mammals alive, with the former evolving into modern-day birds (consider the conditions his ancestors had to survive the next time you see that fat fluffy robin). Ultimately, our survival would be determined by the size of the object the universe sent to annihilate us; a rock the size of a house would have roughly the impact energy of the atomic bomb dropped on Hiroshima, and would flatten anything within about a kilometre. Something the size of a 20-story building, equating to the largest modern nuclear weapons, would wipe out a city and cause extensive climatic effects, but not quite an extinction. An impact of this extent is expected to happen roughly every 2,000 years (the most recent occurred in what is now Saudi Arabia in the 1800s). Once an asteroid reaches the size of Chicxulub, catastrophic effects are seen globally, but scientists estimate that some humans would survive. It’s thought it would take an impact from something about 100 km wide to totally wipe out life on earth.

These doomsday scenarios assume, of course, that we do nothing to avoid them. This is precisely what makes them attractive contexts for disaster films – they’re the only natural disaster that we could entirely evade with the right collective action, creating the potential for a happy ending. NASA and related organisations do have contingencies for this scenario, most recently with the launch of the DART spacecraft in November whose objective is to smash into a distant asteroid and measure how much its orbit is affected. These sorts of tests are crucial to developing what would be our front-line defence in the event of Don’t Look Up proving prophetic. Let’s hope then, that the apathetic public reaction presented in the film doesn't prove just as prophetic.

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