Rare Double Meteorite Strike

Around 470 Million years ago, two asteroids collided in the asteroid belt between the planets Mars and Jupiter.  This sent fragments everywhere, and millions of years later these fragments moved into the inner solar system, many of which struck the Earth as meteorites.  Recently, in Jämtland county, Sweden, a team of geophysicists has identified a pair of impact craters that were formed at the same time, likely from two separate impactors.  One of the craters is a massive 7.5 Km across, while the other is smaller at 700 meters.  This is the first time a double impactor has been scientifically confirmed on Earth.

Illustration of impact resulting in unique double crater in Sweden. Credit: Don Dixon/Erik Sturkell/University of Gothenburg

“The two meteorite impacts occurred at the same time, 458 million years ago, and formed these two craters,” says Erik Sturkell, Professor of Geophysics at the University of Gothenburg. “Information from drilling operations demonstrates that identical sequences are present in the two craters, and the sediment above the impact sequences is of the same age. In other words, these are simultaneous impacts.”

At the time of the impact, area was under water, and so the two meteorites struck water, creating massive waves and huge craters that were initially dry. “The water then rushed back in, bringing with it fragments from the meteorites mixed with material that had been ejected during the explosion and with the gigantic wave that tore away parts of the sea bed,” says Sturkell.

When large meteors collide with the Earth, they can break up into several pieces and impact a large region, though there is usually one larger impactor.  There is no evidence showing that any impactor could split into two main pieces, unless perhaps an asteroid with a tiny moon hit the Earth, but that theory hasn’t been proven either.  This is why the finding of a double crater is so rare.   Could the smaller impactor be a broken piece of the larger one?  Could it have been a tiny moon orbiting the larger fragment?

Looking at other worlds, we see tons of craters varying in age, up to several billion years old.  But back home on Earth, geological and meteorological processes slowly break down the signs of craters, reforming the Earth’s crust.  But the signs remain for hundreds of millions of years, and the signatures of these impacts remain in the rock, waiting for geologists to uncover.  What other mysteries lie beneath our feet?

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