A NASA glaciologist has discovered a possible second impact crater buried under more than a mile of ice in northwest Greenland.
This follows the finding, announced in November 2018, of a 19-mile-wide crater beneath Hiawatha Glacier – the first meteorite impact crater ever discovered under Earth’s ice sheets.
Before the discovery of the Hiawatha impact crater (see video below), scientists generally assumed that most evidence of past impacts in Greenland and Antarctica would have been wiped away by unrelenting erosion by the overlying ice.
To confirm his suspicion about the possible presence of a second impact crater, MacGregor studied the raw radar images that are used to map the topography of the bedrock beneath the ice, including those collected by NASA’s Operation IceBridge.
Though the structure isn’t as clearly circular as the Hiawatha crater, MacGregor estimated the second crater’s diameter at 22.7 miles.
Although the newly found impact craters in northwest Greenland are only 114 miles apart, they do not appear to have been formed at the same time.
“The ice layers above this second crater are unambiguously older than those above Hiawatha, and the second crater is about twice as eroded,” MacGregor said.
To calculate the statistical likelihood that the two craters were created by unrelated impact events, MacGregor’s team used recently published estimates that leverage lunar impact rates to better understand Earth’s harder-to-detect impact record.
“This does not rule out the possibility that the two new Greenland craters were made in a single event, such as the impact of a well separated binary asteroid, but we cannot make a case for it either,” said William Bottke, a planetary scientist with the Southwest Research Institute in Boulder, Colorado, and co-author of both MacGregor’s paper and the new lunar impact record study.
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