o a team was sent to Greenland to collect superior, higher-resolution ice-radar data of the Hiawatha glacier and the bedrock beneath. This was accomplished in 2016 using wideband ground-penetrating radar (or in this case, ice-penetrating radar) developed at the University of Kansas.
That said, signs of the impact crater were also visible to the naked eye.
“You can see the rounded structure at the edge of the ice sheet, especially when flying high enough,” John Paden, a co-author of the study and an engineer at the University of Kansas, said in a statement. “For the most part the crater isn’t visible out the aeroplane window. It’s funny that until now nobody thought, ‘Hey, what’s that semicircular feature there?’ From the aeroplane it is subtle and hard to see unless you already know it’s there. Using satellite imagery taken at a low sun angle that accentuates hills and valleys in the ice sheet’s terrain—you can really see the circle of the whole crater in these images.”
An illustration of an aeroplane using radar to map the topography below the ice sheet. (Image: NASA)
Next, the scientists visited the edge of the glacier to collect river samples. Some of the minerals they analysed exhibited the telltale characteristics of a catastrophic impact, such as shocked quartz grains and other impact-related grains, such as glass.
Some pre-glacial channels were seen below the ice sheet at the site of the crater, which suggests the Greenland Ice Sheet was already in place when the asteroid struck. The exact timing of the asteroid strike, however, is fairly vague, with the researchers saying it happened between 3 million and 12,000 years ago. But preliminary evidence suggests it happened relatively recently. The crater appears to be well-preserved—a surprising observation given that ice is a powerful erosive force. The crater is likely fairly young from a geological perspective.
“It is correct that the crater is not well dated but there’s good evidence that it is geologically young, that is, it formed within the last 2 to 3 million years, and most likely it is as young as the last Ice Age [which ended around 12,000 years ago],” Larsen explained to Gizmodo. “We are currently trying to come up with ideas on how to date the impact. One idea is to drill through the ice and get bedrock samples that can be used for numerical dating.”
An example of the topographic data used in the new study. (Image: University of Kansas)
Also, the incident was severe enough such that evidence of the impact should be detectable elsewhere on the planet. The impact likely triggered a global cooling event by delivering copious amounts of debris, dust, and water vapour into the atmosphere, blocking incoming solar radiation. At the same time, melting ice from Greenland’s ice sheet would have reached the North Atlantic, causing a weakening or shutting down of the North Atlantic current—the current that provides western and northern Europe with its relatively mild climate. Evidence of the impact should thus exist within our planet’s stratigraphy, allowing for more precise dating of the impact. Archaeologists and anthropologists could also help in this regard, to see if and when ancient populations of humans were affected by an asteroid strike dating back to this time period.
The discovery of this previously unknown impact crater in Greenland is welcome news, both in terms of our learning about it, and the future scientific work it’s sure to inspire. Confirming the existence of this crater is just the first step—there’s now plenty of related work to be done. [Science Advances]