How scared should you be of an asteroid hitting Earth?

Somewhere, in the cold depths of space, there is a space rock that could destroy a large chunk of life on Earth. Is this fate inevitable? Can we find a way to stop it, or will we end up suffering 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 megatsunamis, ignite huge wildfires and darken skies around the world. Asteroids of this size are estimated to hit Earth approximately every 60 million years, based on the planet’s crater record. For the next size class below, asteroids about 1 kilometer in diameter, estimates suggest they hit Earth about every million years, with the most recent being about 900,000 years ago. Those numbers are enough to make you nervous.

But one of the things that sets humans apart from the dinosaurs is our ability to look into space and interpret what we see there. Naturally, scientists around the world have taken advantage of this ability to try to figure out how many asteroids are out there and what proportion of them are on trajectories that could be dangerous.

The good news is that of the thousands of near-Earth objects that astronomers monitor, 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 them still have an extremely low chance of coming for us, and almost all of them are less than 100 meters in diameter. So will an apocalyptic asteroid strike in our lifetime? Almost certainly not.

However, the eagle-eyed reader will notice warnings like “asteroids we’re tracking” and “small chance” and “almost” and “almost” and not yet hear a sigh of relief accordingly. That’s largely because we can’t be sure we’ve detected every asteroid, as breathless headlines regularly show that a newly found rock is heading straight for Earth — even though they’re usually not that close to the minute 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 we’ve searched, and the power of our telescopes. With their help, it is estimated that we have spotted all asteroids 10 kilometers in diameter or larger that could pose a danger to Earth, so you can now breathe a sigh of relief: it is highly unlikely that we will suffer the same fate as the dinosaurs.

We’ve detected about 80 percent of the 1-kilometer-diameter asteroids, so it’s pretty unlikely that any of them would turn up unexpectedly. Anything less than 100 meters is a negligible hazard and would likely burn up in the atmosphere on its way in, or cause less damage if it did hit, like the 2013 Chelyabinsk meteor.

However, the 100-meter “city killers” are a bigger problem, as we’ve uncovered less than half of them to be lurking around. If you’re going to be afraid of asteroids, these are the ones.

Fortunately, there’s one more thing that sets us apart from the dinosaurs: the technology we’ve developed to actually get into space. The first way they protect us is through space telescopes that track any space rocks that might be on their way to Earth. All kinds of telescopes are keeping watch while they make their next observations, but a special telescope called the NEO Surveyor is scheduled to launch next year, which should drastically improve the number of asteroids we can observe.

The second way spaceflight protects us is by providing options should we actually find something headed for impact. NASA’s 2022 Double Asteroid Redirection Test hit an asteroid to throw it off course, proving that we can actually move one of these space rocks if we have to. If we spot one approaching us with enough time to spare, which would mean at least a few years, we should be able to shift its trajectory so that it misses.

If we could not prevent an asteroid from hitting Earth, it would be a natural disaster, but a predictable one. It would likely hit an ocean or an uninhabited area—after all, according to World Economic Forumless than 15 percent of the world’s landmass (which is less than 4.3 percent of its total area) has been modified by humans, much less inhabited.

If the asteroid were headed for one of the few populated areas, we would have the same options we have for any natural disaster: evacuate, mitigate, shelter in place. Strengthening our disaster response capabilities would help prepare for this possibility, with the useful side effect of helping us respond to many other disasters that are more likely and more difficult to predict.

So back to the questions that started it all. Is an asteroid inevitable? Absolutely. Is there any solution? Very possible. Are we finally facing the same fate as the dinosaurs? If so, 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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