June 12 – Wham Bam

Today’s factismal: The Earth gets hit by about 42,000 meteorites each year.

Ask any third grader what killed the dinosaurs and odds are she’ll tell you that an asteroid did it. (That’s not quite correct but it is close enough for now.) And if the third grader is especially clever, she may even know the name of the asteroid: Chicxulub (“Chick-sue-loob” or “the well of the great horns”). Like all major impact structures, the name comes from the closest town and not from the actual asteroid; those are usually given names like 2060 Chiron or 1992 QB1 or 1999 FN53. But what your third grader may not know is that Chicxulub was hardly the only asteroid to every hit the Earth.

Every day, nearly 170 meteorites hit the Earth; that adds up to 42,000 meteorites each year! (For the purposes of this article, we’ll treat asteroids and meteorites and comets as being roughly equivalent simply because they are, planetologically speaking.) Most of these are small pieces of rock and ice about the size of a grain of rice that burn up in the outer atmosphere leaving nothing behind but a little dust and a pretty lightshow. But about 2,800 of those meteorites each year are large enough to actually make it deeper into the atmosphere.

A meteorite as seen from above the atmosphere  (Image courtesy NASA/Ron Garan)

A meteorite as seen from above the atmosphere
(Image courtesy NASA/Ron Garan)

Every year, about 500 meteorites survive their fiery plunge through the atmosphere and make it to the ground. Most of those are small and do little damage, but every once in a while we get something a little larger that causes trouble. In 2013, a meteor that was 60 ft across and weighed more than the Eiffel tower fell above Chelyabinsk, Russia. When it exploded in the sky, it created a shockwave that shattered glass for miles around, injuring more than 1,500 people who had gone to the window to see what the pretty bright light was. When it was all over and done, the Chelyabinsk meteor left behind $33 million in damages, more than 1,500 pounds of fragments, and a 20 ft wide hole known as an “astrobleme” (star wound) in the trade or a “meteor crater” to news reporters.

And that isn’t the worst that could happen. Based on what we know right now, scientists expect to see an impact creating a Chelyabinsk style crater roughly every 250 years, an Odessa style 500 ft crater every 540 years, a Wolfe Creeksized half-mile across crater every 13,000 years, a (Barringer) Meteor Crater mile-wide crater every 21,000 years, a Pingualuit two mile across impact every 50,000 years, and a Chicxulub 110 mile across crater every 100,000,000 years. As you might guess from that big gap at the end, there is still a lot that we don’t know for sure about impact craters.

The Pingualuit impact crater (Image courtesy NASA)

The Pingualuit impact crater (Image courtesy NASA)

But we can learn. And surprisingly on of the best places to learn about impact craters is from the things that make them – asteroids! That’s because unlike the Earth, which has wind and water and plate tectonics to erase old impact craters, the asteroids just have impacts to erase other impacts. So by examining impact craters on asteroids, we can learn more about how they happen on Earth which can help us keep another Chicxulub from knocking on our planet one day. If you’d like to learn more about imact craters on asteroids, why not zoom over to Vesta Mappers at Cosmo Quest? They’ll show you how to identify impact craters on the latest images of Vesta and then let you loose on the newest data we’ve got!


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