A glaciologist has discovered another enormous impact crater under more than a mile of ice in Greenland. This is on the heels of the November 2019 discovery of an impact crater in the same area under the Hiawatha Glacier. The November discovery was the first-ever crater found under ice on Earth.
The two craters are only 183 km (114 miles) apart. The November crater is 30.5 km (19 miles) wide, while the new one is 35.4 km (22 miles) wide. If the newer one can be definitely confirmed as an impact crater, it will be the 22nd largest one on Earth.
Joe MacGregor is the glaciologist who discovered this new crater. He works at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. He was also involved with the first discovery. The discovery of this new crater was published in a paper in Geophysical Research Letters on February 11th.
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The geology of the polar regions of Earth is not well-understood. Thick sheets of ice obscure the rock and surface features. But thanks to aerogeophysical data and satellite data, scientists are starting to get a better picture of it. Finding craters is of great interest because they can have such global impact on climate history.
A previous 2015 study looked at the inventory of impact craters and concluded that finding any more craters of this size was improbable, but not impossible. That study said that finding any more craters larger than 6km was not very likely, (though we will probably find another 90 craters between 1km and 6km in width.) That finding was based largely on erosion rates.
But deep under the ice, erosion rates are different. Will we find even more of these larger craters under the ice?
In an interview with NBC News, MacGregor said, “Once we knew from Hiawatha that there could be craters under ice sheets, it was quite easy to find the next one using an ensemble of publicly available NASA data.”
The scientists used elevation, texture, and topography data, as well as magnetic and gravitational data, to look for more impact craters. According to MacGregor, it wasn’t difficult to identify the potential second crater.
Since the two craters are so close together, the team wondered if the two were from the same event. Though they are of similar size, there are notable differences. The second crater appears to be more eroded, and the ice over it is much less disturbed. In the paper the authors say, “Statistical analysis of the frequency of two unrelated but nearby large impacts indicates that it is improbable but not impossible that this pair is unrelated.”
Asteroids are known to exist in binary pairs. About 15% of near-Earth asteroids are binaries. So it’s possible that the pair of craters are twins. However, surveys of the near-Earth asteroid populations haven’t found any binary pairs of equally-sized asteroids. Statistically speaking it is unlikely that these two are pairs.
There are two other pairs of craters on Earth: the first pair is the Boltysh and Obolon craters in the Ukraine, the second is the Clearwater Lakes craters in Quebec, Canada. Those pairs were thought to be twins from the same events, but Argon dating and other techniques revealed large age differences between them.
The same techniques can’t be used to determine the ages of these two new craters under the ice, but much of the detailed data in the study suggest they are not the same age. For example, the overlying ice appears to be a different age for each crater. Over the first crater, the ice appears to be no older than 12,800 years, while over the newly-discovered crater, the ice appears to be at least 79,000 years old.
This finding is still awaiting confirmation, but the morphology clearly resembles an impact crater. The question is, how many more of these craters will we find buried under the ice on Earth?
Will we find others, and will they be linked to shifting climate in Earth’s history? Will they be linked to extinctions, like the Chicxulub impact that caused so much trouble for the dinosaurs?
Who knows. But with improved remote sensing technology, we’ll find them if they’re there.