Science & Technology

We Just Found a City-Sized Asteroid Crater Hiding Under Greenland's Ice

Everyone knows that a giant asteroid killed (most of) the dinosaurs. And this 1980 Chevy Malibu is proof that it wasn't the last chunk of rock to crash down to the surface of the planet. Now, a new discovery suggests that a meteorite impact has been hiding practically in plain sight since the end of the last geological era. And it's friggin' huge.

Related: A 30,800-Kilogram Meteorite Unearthed in Argentina

Map of the bedrock topography beneath the ice sheet and the ice-free land surrounding the Hiawatha impact crater. The structure is 31 km wide, with a prominent rim surrounding the structure. In the central part of the impact structure, an area with elevated terrain is seen, which is typical for larger impact craters. Calculations show that in order to generate an impact crater of this size, the earth was struck by a meteorite more than 1 km wide.
Close-up of the northwestern ice-sheet margin in Inglefield Land. The Hiawatha impact crater was discovered beneath the semi-circular ice margin. The structure is also imprinted on the shape of the ice surface, even though it lies nearly 1,000 meters below the ice surface. Hiawatha is named after outlet glacier at the edge of the ice sheet. The name was given by Lauge Koch in 1922 during an expedition around northern Greenland, while thinking of the pre-colonial Native American leader and co-founder of the Iroquois Confederacy.

Right Before Our Very Ice

If you've ever flown a small plane over the northern edge of Greenland — we're not saying you have, we're saying if — you might have noticed a strange, nearly perfect circle of smooth ice atop one of the glaciers creeping slowly toward the Arctic ocean. Or you might not have. It's actually pretty difficult to see from an airplane — considerably harder than a polar bear in a blizzard. But when researchers took a look at satellite imaging of the area that was gathered when the sun was low in the sky, the large, smooth section stood out against the hilly regions all around it.

This smooth section is on a chunk of ice known as Hiawatha glacier, and the team led by Brendan Lynch from the University of Kansas went looking at the satellite images because they'd already spotted something odd from radar images of the area. The circle, which measures 19.26 miles (31 kilometers), is hiding a massive depression in the ground. Kurt Kjær and his team from the University of Copenhagen returned to the area to map the tectonic plates and collect sediments in the area. When they examined the quartz sand, they found the type of deformation you'd find if there had been a massive impact some time ago. That was all the evidence the researchers needed: This depression was created by a meteorite — likely about 1 kilometer (0.62 miles) across and made of iron, based on the size of the crater and minerals found in the area.

This is a photo illustration of the airplane during the survey, radar waves and the actual radar image.
Geomorphological and glaciological setting of Hiawatha Glacier, northwest Greenland. (A) Regional view of northwest Greenland. Inset map shows location relative to whole of Greenland. Magenta box identifies location of panels B-D. (B) 5-m ArcticDEM mosaic over eastern Inglefield Land. Colors are ice surface velocity. Blue line illustrates an active basal drainage path inferred from radargrams.
(C) Hillshade surface relief based on the ArcticDEM mosaic which illustrates characteristics such as surface undulations. Dashed red lines are the outlines of the two subglacial paleo-channels. Blue lines are catchment outlines, i.e., solid blue line is subglacial and hatched is supraglacial. (D) Bed topography based on airborne radar sounding from 1997-2014 NASA data and 2016 AWI data. Black triangles represent elevated rim picks from the radargrams and the dark purple circles represent peaks in the central uplift. Hatched red lines are field measurements of the strike of ice-marginal bedrock structures. Black circles show location of the three glaciofluvial sediment.

A Record Writ in Stone

Although they haven't quite been able to date the crater yet, researchers place it somewhere between 12,000 and three million years old. This isn't the first time that scientists have suspected a massive meteor strike sometime in the range of 12,000 years ago. After all, that was about the time that the megafauna of the Americas suddenly went extinct.

In 2007, researchers dug deep into the question of what killed the mammoths, sabertooth cats, and other giant mammals — literally. Underground, there was a strata of spherules — hardened droplets of once-molten rock — mixed into clay that some people theorized were cosmic in origin. Unfortunately, earth scientists weren't very convinced. The most damning piece of evidence they offered? Many of those "spherules" turned out to be fungal spores and not the alien kind you'd find in a comic book. But even if the mammoth-killing impact theory is bunk, this new discovery suggests that a massive meteorite could have hit the planet around the same timeframe.

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The earth is riddled with space rocks every day. See some of the most fascinating specimens in Caroline Smith's "Meteorites." We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

Written by Reuben Westmaas November 14, 2018

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