Saturday , May 8 2021

Meteor craters found under Greenland ice



An international team of researchers, including NASA glaciologists, have discovered large meteorite craters that hide under more than half a mile of ice in northwest Greenland.

The crater – the first of any size found under the Greenland ice sheet – is one of the 25 largest impact craters on Earth, measuring around 1,000 feet and having a diameter of more than 19 miles.

The group, led by researchers from the University of Copenhagen GeoGenetics Center at the Danish Natural History Museum, worked for the past three years to verify their findings, which they initially did in 2015 using NASA data. Their findings are published in the November 14 issue of the journal Science Advances.

"NASA makes the data it collects freely available to scientists and communities around the world," said Joe MacGregor, NASA glaciologist at Goddard Space Flight Center, who was involved in the investigation at an early stage. "That set the stage for the moment & # 39; Eureka & # 39; our Danish colleagues."

The researchers first saw the crater in July 2015, when they were examining a new map of topography under the Greenland ice sheet that uses ice penetrating radar data mainly from NASA's IceBridge Operation – multi-year missions in the air to track changes in polar ice – and missions previous NASA air in Greenland. Scientists pay attention to the previously untested circular depression beneath the Hiawatha Glacier, sitting on the edge of the ice sheet in northwest Greenland.

Using satellite imagery from the Moderate Resolution Imaging Spectrophotometer instrument on NASA's Terra and Aqua satellites, MacGregor also examined the ice surface in the Hiawatha Glacier region and quickly found evidence of circular patterns on the ice surface that matched those observed on the bed. topographic maps.

To confirm their suspicion, in May 2016 the team sent a research plane from the German Alfred Wegener Institute to fly over the Hiawatha Glacier and map the craters and ice above it with the latest ice penetrating radar provided by the University. from Kansas. MacGregor, who is an expert in radar ice measurements, helped design aerial surveys.

Radar data from an intensive aerial survey of the Hiawatha crater in May 2016 are displayed here in aqua colored curtains. The blue arrow points to the top of the center of the crater.
Credit: NASA / Cindy Starr

"Previous radar measurements from the Hiawatha Glacier were part of NASA's long-term efforts to map Greenland ice changes," MacGregor said. "What we really need to test our hypothesis is a dense and focused radar survey there. This survey exceeds all expectations and portrays depression in stunning detail: clear circular rims, central lift, disturbed and undisturbed ice sheets, and basal debris – all there. "

Craters were formed less than 3 million years ago, according to research, when an iron meteorite that was more than half a mile wide hit northwestern Greenland. The resulting depression is then covered with ice.

"This crater is well maintained and that is surprising because glacier ice is a very efficient erosive agent that will quickly eliminate its impact footprint," said Kurt Kjær, a professor at the Center for GeoGenetics at the Natural History Museum of Denmark and lead author of the study.

Kjær said the condition of the crater showed that the impact might even have occurred towards the end of the last ice age, which would place craters produced among the youngest on the planet.

In the summer of 2016 and 2017, the research team returned to Hiawatha Glacier to map tectonic structures in the rock near the foot of the glacier and collect sediment samples that were swept away from depression through melt drains.

"Some quartz sand originating from the crater has a planar deformation feature that signifies the impact of violence; this is convincing evidence that depression under the Hiawatha Glacier is a meteorite crater, "said professor Nicolaj Larsen of Aarhus University in Denmark, one of the study's authors.

Previous research has shown that major impacts can greatly affect Earth's climate, with major consequences for life on Earth at that time. Researchers plan to continue their work in this area, answering the remaining questions about when and how the impact of meteorites on Hiawatha Glacier affects the planet.

Image shown: The Hiawatha impact crater is covered by Greenland Ice Sheet, which flows just outside the crater lip, forming a semicircular edge. This edge (the top of the photo) and the ice tongue that pierces the crater rim are shown in a photo taken during a NASA Operation IceBridge flight on April 17.

Credits: NASA / John Sonntag

Two views of the Hiawatha crater region: one is covered by Greenland Ice Sheet, the other shows the topography of the rock under the ice sheet, including the crater.
Credit: NASA / Cindy Starr


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