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In a remote area of northwest Greenland, [music rises]

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an international team of scientists has

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made a stunning discovery, buried beneath a kilometer

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of ice. It’s an impact crater …

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300 meters deep … 31 km wide

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… much bigger than Washington, D.C.,

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even bigger than Paris, and it’s probably

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one of the youngest large impact craters on Earth.

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The relentless spread of the Greenland Ice Sheet has covered the crater, obscuring

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obscuring it from view for thousands if not hundreds of thousands of years.

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Even so, scientists say it was essentially hiding in plain sight.

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So what finally revealed its presence?

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It all started with a rock … a map …

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and a connection made by scientists at the Natural History Museum in Copenhagen.

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Each day, scientists there pass by a large

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iron meteorite found in Greenland decades ago.

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One day, they got a new map of the bedrock topography beneath the ice sheet,

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mostly based on ice-penetrating radar data collected

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onboard NASA’s P-3 aircraft over two decades. [Sound of aircraft engine]

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This map gets more refined all the time, yet there are still areas open

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to interpretation, including the conspicuously semicircular

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edge of the ice sheet, drained by the Hiawatha Glacier.

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There, the data showed a circular depression in the bedrock,

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near the region where that courtyard meteorite had been found.

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In May of 2016, the team sent the German research plane

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Polar 6 to fly over Hiawatha Glacier with a powerful new

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ice-penetrating radar.

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Radar waves can travel through the ice, measuring its thickness

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and internal structure. Studying data from this airborne survey,

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the scientists confirmed the telltale bowl shape and central peaks

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beneath Hiawatha Glacier. They also found that the oldest ice

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in this crater was actually fairly young, by Greenland standards,

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and had experienced a great disturbance in its flow toward the end

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of the last ice age. [Sound of hammer on rock]

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The team then visited the area on foot, and in sediments deposited by a river

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draining out of the glacier, they found grains of the mineral quartz that showed signs

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of being physically shocked in a massive impact.

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Models suggest, the asteroid was more than a kilometer wide.

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The Hiawatha crater is one of the 25 largest known

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impact craters on Earth, and the first found under any of

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our planet’s ice sheets.Crucially, the Hiawatha impact

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crater still looks like an impact crater, even though it’s covered by ice

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and seems to be rapidly eroding. The data as a whole

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suggests it’s quite young – geologically speaking

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But we don’t know exactly when an asteroid sped

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toward Earth, through the atmosphere, and into the

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planet’s crust in Northwest Greenland. [Sound of impact]

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It was likely less than 3 million years ago.

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But it might have been as recently as during the last ice age,

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12 to 115 thousand years ago.

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The impact could have also occurred when ice already covered Greenland

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and it would have instantly vaporized billions of tons of ice and re-routed

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the flow of ice and water into the ocean.

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Whenever the impact happened, life on Earth at the time would have been profoundly affected.

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An impact of this size is unlikely

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to happen again soon, but evidence that it might have happened

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not so long ago, in Earth’s history is essential to assessing the risk today.

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This is the first study of the Hiawatha

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impact crater, but it still holds many secrets waiting to be discovered.

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[music fades]