The remnants of an ice age asteroid that slammed into the Earth have been discovered under Greenlands Hiawatha Glacier.
A mile-wide, iron asteroid slammed into northern Greenland as early as 12,000 years ago, creating an impact site with an area similar to that of New York City.
“There would have been debris projected into the atmosphere that would affect the climate and the potential for melting a lot of ice, so there could have been a sudden freshwater influx into the Nares Strait between Canada and Greenland that would have affected the ocean flow in that whole region,” said co-author John Paden, courtesy associate professor of electrical engineering and computer science at Kansas University.
The crater was discovered underneath the Hiawatha Glacier, a Greenland ice sheet 1 kilometre thick, after extensive radar surveys by a Danish group of researchers. Using data gathered by NASA programs mapping the ice, the Danish researchers spotted a peculiar semi-circular depression at the edge of the glacier in 2015.
“We immediately knew this was something special but at the same time it became clear that it would be difficult to confirm the origin of the depression,” said Kurt H. Kjær, lead researcher on the study, published Wednesday in Science Advances.
To do so, the team had to map the crater themselves, but of course they couldnt just shovel all that ice out of the way. By using a German research plane with “next-generation radar” technology the team conducted a more thorough, focused analysis of the site, revealing the bowl-shaped contours of the crater.
But to confirm the crater was created by an asteroid, the scientists wanted some more physical proof. Sifting through the sand at the front of the glacier revealed shocked quartz, a form of quartz created by intense pressures, and other “impact-related grains”.
The findings allowed the team to make some data-driven, preliminary predictions about what might have caused it: A mile-wide, iron-rich asteroid that collided with the Earth, penetrating some 7 kilometres into the crust.
The impact initially caused a cavity that was around 20 kilometres in diameter, before collapsing into the 800 metre deep, 31 kilometre-wide site we see today.
But when did the asteroid hit the Earth? The team arent quite sure of that yet. They know it happened sometime in the Pleistocene, but thats an epoch that spans 2 and a half million years of history. Current estimates, based on the geological profile, seem to suggest that crater is quite young, but further analysis is required.
“This will be a challenge, because it will probably require recovering material that melted during the impact from the bottom of the structure,” said Kjær.
Accurately dating the collision will provide future research with a better understanding of the consequences of such an impact and how it affected the environment on the Earth.
An iron-rich asteroid measuring nearly a kilometer wide (0.6 miles) struck Greenlands ice-covered surface at some point between 3 million and 12,000 years ago, according to a new study published today in Science Advances.
Location of the Hiawatha impact crater.Image: University of Kansas The impact wouldve flung horrific amounts of water vapor and debris into the atmosphere, while sending torrents of meltwater into the North Atlantic—events that likely triggered global cooling (a phenomenon sometimes referred to as a nuclear or volcanic winter). Over time, however, the gaping hole was obscured by a 1,000-meter-tall (3,200-foot) layer of ice, where it remained hidden for thousands of years.
Remarkably, the crater was discovered quite by chance—and its now the first large crater to be discovered beneath a continental ice sheet.
In 2015 I was looking at a new map of the bedrock below the Greenland Ice Sheet and discovered a large circular feature under the Hiawatha glacier in northwest Greenland, Nicolaj K. Larsen, a co-author of the study and a geoscientist at Aarhus University, told Gizmodo. In other words, it was a coincidence that the crater was discovered.
Larsen, along with his colleague Kurt Kjaer from the Natural History Museum of Denmark, immediately recognized that they had stumbled upon something special, but it soon became apparent that the depression would be hard to confirm as a remnant of an ancient asteroid strike.
Map of the bedrock topography beneath the ice sheet and the ice-free land surrounding the Hiawatha impact crater.Image: The Natural History Museum of DenmarkAdvertisement
The first step was to analyze aerial surveys taken of Greenland from 1997 to 2014 by researchers from the University of Kansas. But the data resolution of these surveys was not sufficient, according to Larsen, so 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.
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 isnt visible out the airplane window. Its funny that until now nobody thought, Hey, whats that semicircular feature there? From the airplane it is subtle and hard to see unless you already know its there. Using satellite imagery taken at a low sun angle that accentuates hills and valleys in the ice sheets terrain—you can really see the circle of the whole crater in these images.
An illustration of an airplane using radar to map the topography below the ice sheet. Image: NASANext, the scientists visited the edge of the glacier to collect river samples. Some of the minerals they analyzed 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 theres 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 KansasAlso, 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 vapor into the atmosphere, blocking incoming solar radiation. At the same time, melting ice from Greenlands ice sheet wouldve 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 planets 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 its sure to inspire. Confirming the existence of this crater is just the first step—theres now plenty of related work to be done.
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