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Here's What Would Happen If an Earth-Sized Asteroid Hit Earth

There's a calculator for asteroid impact.
January 26, 2015, 9:18pm
​There goes the neighborhood. Image: Don Davis/NASA.

​This morning, an enormous space rock missed Earth by a narrow margin of 745,000 miles, or about three times the distance from the Earth to the Moon. With a diameter of 550 meters and a velocity of about 35,000 miles per hour, the asteroid, known as 2004 BL86, will be so bright in the evening sky that it will be visible through binoculars. Scientists don't expect another object of this size to pass so closely to Earth until August 7, 2027.

This time around, we got lucky. But speculatively speaking, what if asteroid 2004 BL86 wasn't a passing curiosity? What if it hurtled towards us just a little earlier, and instead of flying freely through the wake of Earth's orbit, it collided with us head on? How bad would the damage be?

Trajectory of the flyby. Image: NASA/JPL-Caltech.

Fortunately, there is an online tool for calculating the apocalyptic potential of various impact scenarios. Run by Purdue University, Impact Earth allows users to input details about asteroids, comets, and other cosmic death traps, then crunches the numbers on the fallout.

I gave the calculator the known details about asteroid 2004 BL86, including its diameter and velocity. I entered a hypothetical mid-range angle of 45 degrees, and specified that the asteroid hit sedimentary land, not water. Then, I asked it to tell me what the damage would be like one kilometer away from the impact site. After a dramatic animation of an asteroid hitting New England, Impact Earth gave me a rundown of the designer catastrophe.

Naturally, it wasn't pretty. "The projectile begins to breakup at an altitude of 49,800 meters (16,3000 ft)," Impact Earth predicted. It would be fractured by the time it hit the ground, striking the surface at a velocity of about 7.95 miles per second.

The energy released would be about 5,120 megatons, which is 100 times more powerful than the strongest nuclear bomb ever detonated. It would leave behind a crater with a diameter of 3.64 miles and a depth of 1.26 miles—similar dimensions to Alabama's Wetumpka crater. But as the calculator noted under the "Global Damage" category, the impact would not be enough to disrupt the Earth on a global level by altering its orbit or its axial tilt.

An ocean impact. Image: NASA.

I input the numbers again, this time getting the tool to project what would happen if I was standing 500 kilometers (310 miles) away from the impact. This time it gave me a lot more information about the far-reaching effects of the disaster (from what I gathered, standing one kilometer away pretty much amounted to instant vaporization).

The most immediate effect would be a massive earthquake, which would arrive about 1.67 minutes after the impact and would register 7.1 on the Richter scale. Then, a storm of ejected dust particles would rain down on my new position about six minutes after the impact. Finally, a loud, 67 decibel airblast would blow past my location about 25 minutes after the impact.

In short, the collision would be a terrifying natural disaster that would wreak havoc on communities for thousands of miles around the impact site. While that's not exactly surprising, it is interesting to curate the details of the catastrophe on such a sophisticated online tool.

It's also kind of addictive. After modeling the potential 2004 BL86 collision, I immediately wanted to design even crazier impact events. After modelling the dinosaur-destroying Chicxulub impact and throwing an object the size of Australia into shallow coastal waters, I decided to go all out and throw another Earth at Earth.

Concept drawing of Chicxulub impact. Image: NASA/JPL-Caltech.

So in case you're wondering what would happen if a planetary twin were to impact at the speed of our own orbit, here is what the calculator had to say about it: "The Earth is completely disrupted by the impact and its debris forms a new asteroid belt orbiting the Sun between Venus and Mars."

"100 percent of the Earth is melted," the rundown continued. "Depending on the direction and location the collision, the impact may make a noticeable change in the tilt of Earth's axis (< 5 degrees). Depending on the direction and location of impact, the collision may cause a change in the length of the day of up to 1,500 hours. The impact does not shift the Earth's orbit noticeably."

There you have it: the fallout of a planet fight. Earth may be entirely melted and rotationally alien, but goddamn if it's going to budge out of its orbit over a cosmic turf war.