Could this dramatic image ever happen for real?
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Somewhere, out in the cold depths of space, there is a space rock that could destroy a large part of life on Earth. Is this fate inevitable? Can we find a way to stop it, or will we eventually suffer the same fate as the dinosaurs? And should this existential threat keep you up at night? Here’s what we know.
The asteroid that killed the dinosaurs 66 million years ago was at least 10 kilometers in diameter, large enough to cause mega-tsunamis, ignite huge wildfires and darken skies around the world. Asteroids of that size are estimated to hit Earth about every 60 million years, based on the planet’s cratering record. For the next size class down, asteroids around 1 kilometer across, estimates suggest they hit Earth about every million years, with the last being about 900,000 years ago. These numbers are enough to make you nervous.
But one of the things that separates humanity from the dinosaurs is our ability to look out into space and interpret what we see there. Naturally, scientists all over the world have used this ability to try to find out how many asteroids are out there and what proportion of them are in potentially dangerous orbits.
The good news is that of the thousands of near-Earth objects that astronomers track, only about 35 have more than a 1-in-a-million chance of hitting Earth in the next 100 years. The even better news is that all of these still have extremely slim chances of coming after us, and almost all of them are less than 100 meters across. So, will an apocalyptic asteroid hit in our lifetimes? Almost certainly not.
Still, the eagle-eyed reader will have noticed caveats like “of the asteroids we’re tracking” and “small chances” and “almost” and “almost” and consequently won’t be sighing with relief just yet. That’s largely because we can’t be sure we’ve discovered every asteroid, which is regularly proven by breathless headlines saying a newfound rock is heading straight for Earth – even though they’re usually not near misses and pass by harmlessly.
To calculate the proportion of asteroids we’ve found, astronomers use three numbers: the number we’ve found, the volume of sky searched, and the power of our telescopes. Using these, it is estimated that we have discovered all the asteroids 10 kilometers across or larger that could pose a danger to Earth, so now you can breathe a sigh of relief: it is highly unlikely that we will suffer the same fate as the dinosaurs.
Of the asteroids that are 1 kilometer across, we have discovered about 80 percent, so it is quite unlikely that any of them will appear unexpectedly. Anything less than 100 meters poses a negligible hazard and is likely to burn up in the atmosphere on its way in or cause minor damage if it hits, like the 2013 Chelyabinsk meteor.
However, the 100 meter long “city killers” are more of a problem, as we have discovered less than half of them that can prowl around. If you’re going to be worried about asteroids, they’re the ones to worry about.
Fortunately, there’s another thing that separates us from the dinosaurs: the technology we’ve developed to actually go to space. The first way that protects us is through space telescopes that keep an eye on space rocks that may be on their way to Earth. All kinds of telescopes keep watch while they make other observations, but a dedicated telescope called the NEO Surveyor is scheduled for launch next year, and it should drastically improve the number of asteroids we can keep track of.
The other way space travel protects us is by providing alternatives if we actually find something headed for impact. NASA’s 2022 Double Asteroid Redirection test smashed into an asteroid to push it off course, demonstrating that we can actually move one of these space rocks if we have to. If we see one coming towards us with sufficient time to spare, which would mean at least a couple of years, we should be able to change the path so that it passes.
If we failed to prevent the asteroid from hitting Earth, it would be a natural disaster, but a predictable one. Chances are it would hit the ocean or an uninhabited area—after all, according to the World Economic Forum, less than 15 percent of the world’s land area (which is less than 4.3 percent of its total surface area) has been modified by humans, much less inhabited.
If the asteroid was headed for one of the few inhabited areas, we would have the same options as we do for any natural disaster: evacuate, contain, shelter in place. Strengthening our disaster response capabilities will help prepare us for that possibility, with the useful side effect of helping us respond to many other disasters that are both more likely and harder to predict.
So back to the questions that started all this. Is the asteroid inevitable? Absolutely. Is there a solution? Very possible. Will we eventually suffer the same fate as the dinosaurs? If we are, it will be in the distant future. But worrying about it won’t change any of that. Instead of stewing in our anxiety, we can prepare now by learning how best to deal with natural disasters more generally—and let astronomers keep their watchful eyes on the sky.
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