https://www.cnet.com/news/scientists-uncover-massive-asteroid-impact-site-under-greenland-ice-sheet-nasa/

"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 couldn't 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.