Greenland is covered with one of the largest layers of ice on earth, but beneath its frozen exterior, the landscape is stronger than previously thought.
Bury under two kilometers of ice, researchers believe they have found a second huge impact crater hidden in the northwest corner of the world's largest island.
As scientists explore more and more of our planet, it is becoming increasingly rare to find new impact craters, especially in icy locations such as Greenland or the Antarctic.
Before the first Hiawatha impact crater was found in November of last year, most experts only assumed that the evidence of past influence had been destroyed by the relentless erosion of these regions.
So it is quite extraordinary that within a few months we have discovered what two of these rarities look like, both in Greenland.
"We've studied Earth in many ways, both on land, in the air, and from space, and it's exciting that discoveries like this are still possible," says co-author Joe MacGregor, a glaciologist at the Goddard Space Flight Center NASA.
The discovery was made possible by a combination of satellite imagery and radar data that allowed researchers to "see deep under the ice".
Here they noticed a circular pattern, only 183 kilometers from the first impact crater. With a width of more than 36 kilometers, the pattern had similar features as its adjacent impact crater – especially a shallow, bowl-shaped depression surrounded by a raised rim and centrally located peaks.
Although not as clearly defined as the Hiawatha crater. If this second impression turns out to be the fingerprint of a meteorite, it will be the 22nd largest impact crater ever found on Earth – three spots off the Hiawatha Crater.
"The only other circular structure that could approach this size would be a collapsed volcanic caldera," explains MacGregor.
"But the areas of known volcanic activity in Greenland are several hundred miles away, and a volcano should have a clearly positive magnetic anomaly, and we do not see that at all."
But even if it turns out that Hiawatha has a sibling, it is unlikely that the two craters are twins. The authors predict that the second is not only bigger, but also older.
MacGregor and his team analyzed nearby ice cores and concluded that the area had not been disturbed by a strong force for at least 79,000 years. This could mean two things: that the effects took place more than 79,000 years ago; or it happened lately and the disturbed ice has simply flown away.
However, guessing the age of a crater is a difficult business. In this case, the researchers calculated that it would have taken from one hundred thousand years to a hundred million years for the ice to bring the crater to its current shape.
"The ice sheets over this second crater are clearly older than those over Hiawatha and the second crater is about twice as hollow," explains MacGregor.
"If the two formed at the same time, the probably thicker ice over the second crater would be much faster with the crater balanced than Hiawatha."
Statistically, it is not uncommon for two different meteorites to land so close together. Two neighboring craters of different ages have already been found in Ukraine and Canada, and computer models have confirmed that these events are not unsurpassed in the Earth's crater.
"The existence of a third pair of unrelated craters does not surprise much, but we do not consider it unlikely," says MacGregor.
"Overall, the evidence we've collected indicates that this new structure is likely to be an impact crater, but at present it seems unlikely that he is a twin with Hiawatha."
This study was published in Geophysical research letters,