Buried beneath the Yucatán Peninsula of Coastal Mexico lays a massive crater, stretching from the inland far out into the Caribbean sea. It is the second largest impact crater on Earth, measuring 150 km across and 20 km in depth. Geologists estimate the crater was formed 66 million years ago when a colossal asteroid, estimated at 10-15 km in diameter, plummeted through the Earth’s atmosphere striking the surface with the force of 10 billion Hiroshimas. The aftermath following the impact would have been apocalyptic: Models suggest that megatsunamis reaching 100 m in height would have surged outward, reaching as far as mid-Texas. Enormous chunks of flaming debris—some as large as city blocks—would have blasted outward, bombarding the continent for hundreds of miles, likely igniting wild conflagrations that would have engulfed large swaths of both North and South America. Meanwhile, shock waves from the impact would have triggered earthquakes and volcanic eruptions all over the globe, the emissions of which would have combined with the dust cloud formed from the initial impact to create a sudden greenhouse effect, effectively blocking out the sun for the subsequent decade.
Scientists refer to this as the “Chicxulub Impact”, named after the town that now sits at the crater’s center. However, many will be familiar with this event as the leading theory to account for the sudden extinction of the dinosaurs. Scientists estimate that during this period nearly 75% of all species were wiped out, making it one of the largest extinction events in Earth’s history.
This may lead one to ask, could it happen again?
Image Source: The Scientist
While many view the proliferation of nuclear arms, climate change and artificial intelligence as being among the leading existential threats facing humanity, there are many who are equally concerned with asteroids: In Discover Magazine’s 2000 October issue titled “20 Ways the World Could End,” asteroid impact was listed first among potential doomsday scenarios. During an interview with Charlie Rose in 1995, the American astronomer Carl Sagan remarked that among the reasons for humanity to colonize other planets was the possibility that the Earth would be hit by a large asteroid. Swedish philosopher Nick Bostrom in Superintelligence (2014), named asteroid impact among 11 existential threats to humanity, citing it as potentially more dangerous than a wide scale nuclear exchange. NASA even has a department entirely devoted to tracking the path of potentially hazardous asteroids called “Planetary Defense Coordination.”
Fortunately for us, large asteroids the size of the Chicxulub impactor only strike the Earth approximately every hundred million years—so there’s no cause for immediate alarm. Smaller asteroids, however, are much more common. In fact, according to NASA’s estimates, 80–100 tons of meteoroids (small fragments of asteroids) burn up in the Earth’s atmosphere every day. When they are visible, as flashes of bright light across the sky, they are called meteors—or more colloquially, “shooting stars.” Though, every so often, some larger meteoroids survive to reach the surface: these are called meteorites. According to estimates, this only happens about 30 times a year and only very rarely make any noticeable impact on the ground.
What is of most concern is not large asteroids nor small meteorites, but rather mid-sized asteroids. Asteroids of this class, roughly 10–30m in diameter, collided with the Earth once or twice a century, on average. Though not necessarily an existential threat, asteroids of this magnitude still possess the ability to cause considerable damage, especially were one to strike near a populated area. The most recent of these mid-sized asteroids was recorded in 2013 near Chelyabinsk, Russia when an asteroid estimated at 20m in diameter was seen streaking through the sky and exploding in a radiant flash over the city. The energy released from the blast was estimated to be equivalent to 400–500 kilotons of TNT, or 26–33 atomic bombs. One can only imagine the calamity had the asteroid reached the surface. Asteroids of this sort are the primary reason for NASA’s tracking system.
Image Source: Room
Suppose we discovered an Earth-bound asteroid of Chelyabinsk-size or larger, what could be done? Could we stop it? Redirect it? Blow it up? Well, first, more options become available the earlier the asteroid is detected—but these options aren’t as encouraging as one might like. If, say, an earth-bound asteroid was discovered well in advance, some years or decades ahead of its expected collision date, the two most promising defensive strategies are the “kinetic impactor” and the “gravity tractor.” Though they sound technical, they are relatively straightforward. The “kinetic impactor” would require a probe to be sent out to meet the asteroid, then as the probe follows the asteroid, it would smash the asteroid with an object. This would be repeated over the course of several years in order to alter the asteroid’s course enough so that it avoids Earth. The “gravity tractor,” involves a similar process but rather than smash an object against the asteroid, the probe would merely follow the asteroid with a large mass beside it so that the gravitational pull would tug on the asteroid enough to change its trajectory. Though these strategies seem rather feeble and ineffective one has to consider that an incoming asteroid—if spotted years in advance—would only need to be nudged less than an inch per second in order to alter its path enough to miss Earth.
But what if an incoming asteroid were spotted only days or weeks in advance? In this case, neither of the two strategies above could be implemented in time—so, what could we do? A rather simple answer would be to try to blow it up with an atomic bomb, as seen in the movie Armageddon. Unfortunately for us (and the plausibility of that film), an asteroid at that point in its trajectory would be travelling upwards of 12 miles per second, or 70,000km an hour, so not even a nuclear-armed Bruce Willis would be able to shoot it down (let alone land a spacecraft on it?).
Thankfully, NASA’s current ability to track the path of asteroids suggests that any potentially hazardous asteroid would likely be detected well in advance (such as Asteroid Bennu which was recently discovered but isn’t expected to come near Earth until 2135). Moreover, though asteroids may pose an existential threat to humanity at some point in the distant future, as of now, one should be more worried about being struck by lightning or being fatally wounded by a falling coconut—both of which are much more likely to kill you than an asteroid. It is humbling, however, to reflect on the feebleness of mankind when compared to the awesome forces that surround us, and just how precariously our existence is balanced on this pale blue dot, circling a small star, suspended in a vast cosmos.