What If An Asteroid Hit Earth? | Unveiled

What If an Asteroid Hit Earth?

Earth is covered with evidence of past impacts from large asteroids, many of which devastated the planet and its ecosystem. Asteroids can have eccentric speed and orbits, and we don’t always see them coming. It’s certain that one day we’ll have another large impact, but what if that day comes sooner than we think?

This is Unveiled, and today we’re answering the extraordinary question; what if an asteroid hit Earth?

Astronomers are constantly monitoring the night sky for dangerous objects. There are plenty of comets, asteroids, and meteoroids whizzing through space all the time, and many even fall to earth. But it’s usually meteoroids, defined as rocky or metallic objects one meter or smaller in diameter, that actually enter the Earth’s atmosphere. They create phenomena like shooting stars and meteor showers, while being essentially harmless. Asteroids, defined as at least one meter or more in diameter, are a different story. When one comes within 30 million miles of us, it’s classed as an NEO, or “Near Earth Object”; large NEOs are monitored in case they come closer and become PHAs, or Potentially Hazardous Asteroids. If anything is going to smite planet Earth, it will be a PHA. The good news is that with so many scientists dedicated to searching the skies, we’ll more likely than not see a deadly asteroid coming, giving us time to prepare; we’d have much more of a heads-up than with natural disasters like hurricanes or volcanoes.

NASA has several ideas on how we could potentially divert or destroy an asteroid heading towards us, ranging from shooting it down with nuclear bombs to using a gravity tractor to move it onto a safer course. But none of these are methods we have at our disposal just yet. And even if NASA had enough warning to build them in time, there’s no guarantee that they’d work. So, what would we do? If a doomsday asteroid were gunning for Earth and we couldn’t move it out of the way, what would happen to us?

The most obvious point of comparison is the Chicxulub Impactor, the giant asteroid that killed the dinosaurs 66 million years ago. This asteroid is estimated to have been over six miles in diameter and created a blast of thermal energy so strong that everything within a 600-mile radius was obliterated in a matter of seconds. Researchers say that if you were close enough to see it, you would have died. It’s theorized that when the Chicxulub Impactor hit, it threw up so much dirt and debris that the sun was blocked out, leading to an ice age. It also may have caused a tsunami over a thousand feet high and an earthquake measuring at least a 10.1 on the Richter scale. This is significantly stronger than the largest earthquake ever recorded; that was the 1960 Valdivia Earthquake, which measured 9.5. The destruction wrought by the Chicxulub Impactor eradicated over 75% of Earth’s species and was one of the most devastating events in the planet’s history.

But the Chicxulub Impactor was only one asteroid. Roughly four billion years ago, there was an event known as the Late Heavy Bombardment. Though scientists debate its existence, if it did happen, the evidence suggests that Earth, the moon, and the other inner planets were all bombarded with a huge number of asteroids. A true cause has never been pinned down, but theories range from a rogue planet disturbing the asteroid belt to the formation of Uranus and Neptune. If something like this were to happen again, we’d be in more danger than even another Chicxulub-sized asteroid would bring.

No matter what size an asteroid is, there are only two places it can strike Earth: the land or the sea. Lucky for us, 71% of Earth’s surface is water, making it ultimately more likely that an asteroid will land in the ocean. This doesn’t mean that the impact will leave us safe though – far from it. As with the Chicxulub Impactor, it would still be able to create an enormous tsunami. How deadly would depend on how far out the asteroid struck, but coastal evacuations would be necessary. At least we know how tsunamis behave and how to deal with them, and we’ve already experienced tsunamis even larger than the one Chicxulub may have caused in the recent past; the 1958 tsunami in Lituya Bay, Alaska had a run-up height of 1,720 feet and was caused by rockfall from an earthquake. Given, say, 20 years warning of an incoming asteroid, we’d have lots of time to try and chart its trajectory and work out where would be most at risk. This means that even if the tsunami struck an area where tsunamis aren’t common, that is, somewhere far from a fault line or plate boundary, there’d be adequate time to draw up evacuation plans and build defenses. Cities would certainly be destroyed, but with so much prep time, hopefully, few lives would be lost.

But what if it struck land? The two most recent, large asteroid strikes on Earth – the 1908 Tunguska Event and 2013 Chelyabinsk meteor – both did, after all. The Chelyabinsk meteor is unique because it was caught on video and widely reported. It exploded over Russia early on the morning of February 15th, causing an enormous shockwave that shattered windows and damaged buildings. Nobody died, but 1,500 people were injured, almost all as a result of broken glass. By contrast, there were no records or good eyewitness accounts of the Tunguska Event because it was in such a remote part of Siberia. The event had to be reconstructed from the destruction it left behind, which included flattening nearly 800 square miles of forest; the asteroid still exploded far enough above the planet’s surface to avoid leaving an impact crater. But though these two encounters have led to few, if any, human casualties, that doesn’t mean the explosions weren’t potentially deadly. Frighteningly, the Chelyabinsk meteor went undetected until it entered Earth’s atmosphere, and its explosion had a blast yield equivalent to 500 kilotons of TNT, making it at least 26 times more powerful than the atomic bomb dropped on Hiroshima. Tunguska was even more violent, and its blast yield may have been as high as 30 megatons. That’s more than strong enough to level an entire city. The only upside is that at least an asteroid wouldn’t cause vast quantities of radioactive fallout like a nuclear bomb.

That’s not to say there wouldn’t be wide environmental ramifications, though. If there were enough ash and dust to trigger a new ice age, we would definitely start to see extinctions, perhaps even our own. And even if it were smaller, many species endemic to the environment in which it impacted would also be threatened. An asteroid one mile across or bigger – which is still much smaller than the Chicxulub Impactor – could potentially obliterate life on Earth. Smaller asteroids would have effects akin to a huge earthquake or volcanic explosion and could trigger eruptions in its wake. The only silver lining is that we’d have so much time in advance to prepare contingencies.

We’d have to deal with a fiery and violent explosion, deadly earthquakes, enormous tsunamis, widespread deaths and panic, and potentially another mass extinction depending on where the asteroid landed. And that’s what would happen if an asteroid hit Earth.