What If an Asteroid Were on a Collision Course to Hit Earth?

Somewhere in the far reaches of space, a giant hunk of rock is hurtling our way, just biding its time before an extinction-level impact with Earth. Before you run into your bunker or panic-buy a year’s supply of toilet paper, stay calm. We have a plan.

While we’ve encountered deadly asteroids in our past, do we have the technology to stop them in their tracks? What size does an asteroid need to be to wipe us out? Are there any asteroids heading our way in the near future? Should we blow them up or push them out of the way?

Here at What If, we’ve covered asteroid impacts many times, and yes, a lot of people and dinosaurs have died in our videos. But instead of all the doom and gloom, in this episode, we’re fighting back using science and lasers. You might be wondering, are there any deadly asteroids out there coming our way? Well, NASA has identified one potentially threatening asteroid, known as 101955 Bennu, or just ‘Bennu’ for short. Cute.

This ancient asteroid weighs over 71 billion kg (78 million tons) and has a 1-in-2,700 chance of colliding with Earth in the year 2185. Okay, we have a bit of time. But our great, great, great, great, great, great-grandchildren might not. Unless they get their acts together. So how exactly can we prevent an asteroid impact?

Well, there are a few ways to stop an asteroid. Your first instinct might be to blow them up like in the movies. While nuking an asteroid is a possibility, it really all depends on its size. To put this into perspective, it would have taken a nuke 2000 times more powerful than the biggest nuke ever created to destroy the asteroid that killed the dinosaurs.

In the case of the movie Armageddon, if a 1287 km (800 mi) wide asteroid were going to hit Earth in an hour, we would need to blast it with as much energy as the total energy output of the Sun in a day. That’s a lot of firepower. Bruce Willis would have to get out of there pretty quickly or die hard.

In some cases, nuking a large asteroid could do little good, as the graviational pull of its core could pull it all back together. Alright, so if we can’t blow it up, what else could we do?

Excuse me, excuse me! Sorry, but I have a suggestion! Why don’t we just nudge them a bit? Well, that’s not actually a bad idea. Adding or subtracting just 0.03m/s (an inch per second) of velocity to an asteroid can be just enough of a push to keep us out of harm’s way. This could be achieved by an explosion about 300 m (1,000 ft) away from the asteroid. The irradiation from the explosion will cause a layer of the asteroid’s surface to heat up and blow-off, pushing it in the opposite direction.

Another idea is to slam a spacecraft into it at just the right angle. This is known as the kinetic impactor option. Kind of like space billiards.

In the year 2022, this method will be tested on a non-threatening asteroid, just to see if it works. This will be the Double Asteroid Redirection Test, otherwise known as the DART Mission. Nice one NASA, I like darts too. Two spacecraft will head toward a double asteroid called Didymos, accompanied by its smaller companion, Didymoon. Perfect names for your future cats.

One spacecraft will slam into Didymoon in just the right spot and bullseye. It will nudge its orbit just enough to push Didymos away. The other spacecraft will then monitor its orbit and trajectory. Another option is to fly a spaceship close to an asteroid and gravitationally nudge it over time.

But this would be pretty expensive and tricky. And not all of us can maneouvre like Han Solo. So what’s a cost-effective way of stopping an asteroid?

How about a laser? If it can move your cats out of the way, then maybe it could do the same for an asteroid. A numerical study has shown that by firing a powerful laser on an 80 m (264 ft) wide asteroid for a month, it could heat it enough to move it the equivalent distance of two Earths away. As the asteroid’s surface heats up, it ejects material, creating thrust.

NASA’s Planetary Defense Coordination Office has also proposed that a spacecraft could be sent out with a less-powerful laser array to orbit the asteroid. But it would have to get to the asteroid 15 years in advance to pull this off.

Luckily, we can detect threatening asteroids well ahead of time using powerful telescopes. By taking continuous pictures of the sky, astronomers use computers to look for movement across the background of stars. However, some smaller asteroids, like the Chelyabinsk asteroid that struck Russia in 2013, can go unnoticed. This is because smaller asteroids won’t shine as bright as bigger ones. They have to come very close to Earth to be detected by ground-based telescopes.

Thankfully, the Russian meteoroid exploded 30 km (19 mi) above the city of Chelyabinsk before it could do any serious damage. This still resulted in a powerful shockwave that shattered windows and injured around 1,500 people.NASA has classified over 21,000 asteroids and 100 comets as near-Earth objects. Only 2,000 of these are considered potentially hazardous. This means that their orbits are within 7.2 million km (4.5 million mi) of Earth’s. And they have to be bigger than 800 m (.5 mi) to lead to a global catastrophe.

Before you freak out, the odds of being killed by an asteroid are around 1 in 250,000. You’re far more likely to die in an airplane crash or an earthquake. But you’ll sleep better knowing that both the European Space Agency and NASA have panels of experts that have been planning asteroid defense strategies for decades now.