Although it's potentially one of the 25 largest impact craters on Earth, the bowl-shaped cavity didn't begin to reveal itself until quite recently. In 2009, NASA kicked off Operation IceBridge, an ongoing survey of polar ice that's being conducted from the air. A typical flight sees a group of researchers flying at low altitudes over glaciers and ice sheets. Using scientific instruments, the aeronauts measure everything from snow accumulation to glacial surface temperatures.
Ice-penetrating radar is a vital tool of the trade, one that helps determine the thickness and composition of frozen swaths like glaciers. It can also tell us what the terrain beneath them looks like, which enables scientists to create radar-generated maps of the subglacial landscape.
That's how, back in 2015, IceBridge flyover participants observed an enormous depression in the Earth hiding just under the Hiawatha Glacier's outer edge. The hole looked suspiciously like a meteorite-generated crater.
Kurt Kjær, a geologist at the Natural History Museum of Denmark, spearheaded the campaign to map out — and hopefully identify — the long-hidden structure. He's also the lead author of the new study that just revealed its existence to the world.
Right off the bat, the Danish scientist and his international colleagues had lots of quality info to work with: From 1997 to 2014, NASA projects like IceBridge gathered a ton of radar-sounding data on the region where the depression was found.
To obtain fresh intel, the scientists enlisted a German research plane from the Alfred Wegener Institute. The plane was fitted with sophisticated radar equipment (developed by the University of Kansas) and flown repeatedly over the Greenland site in May 2016. The high-tech gear pumped 12,000 radio wave pulses per second into the glacier. That reflected data taught Kjær and company a great deal about the depression — as well as the layers of ice piled above it. Additional research was carried out in 2017.