NASA has detected a massive, ancient crater buried under two kilometers of ice in northwest Greenland. Even more surprisingly, it’s the second crater discovered under the region’s thick ice in recent months.

Stretching across 36.5 kilometers (22 miles), the crater was likely formed by an asteroid impact within the past 2.6 million years, according to a study published Monday in Geophysical Research Letters. If the feature is confirmed to be the fallout out of an asteroid strike, it will rank as the 22nd biggest impact crater known on Earth.

Scientists have identified about 200 impact craters on our planet, but this is only the second time in history that a crater has been detected under an ice sheet. In November, NASA announced that it had spotted the first subglacial impact crater buried under Greenland’s Hiawatha Glacier, located just 183 kilometers away from the new site.

Inspired by that discovery, a team led by NASA glaciologist Joseph MacGregor started scanning Greenland for other craters. The new crater appears to be larger and older than the Hiawatha impact site.

Both features were spotted using satellite imagery and aerial footage captured by NASA’s Operation IceBridge aircraft fleet.

Given their proximity to each other, MacGregor and his colleagues pondered whether these craters may have been formed by the same impact event. Perhaps a binary asteroid system struck Earth, or one asteroid broke up into two pieces during atmospheric entry.

But observations of the new crater’s topography reveal that it is far more eroded than the Hiawatha crater, suggesting that they could not have formed at the same time.

“The second structure's morphology is shallower [and] its overlying ice is conformal and older,” MacGregor and his co-authors write in the study. “We conclude that the identified structure is very likely an impact crater, but it is unlikely to be a twin of the Hiawatha impact crater.”

Read More: Scientists Discover Hidden Asteroid Crater Under a Mile of Greenland Ice

The Hiawatha crater probably formed within the past 100,000 years. It will take more research to constrain the age of the second crater, but odds are it was created within the Pleistocene period, which began 2,588,000 years ago. Based on the estimated age of its ice sheet cover, it was formed at least 79,000 years ago, the team said.

The structure does not yet have an official name, but the authors recommended calling it the Paterson crater. This name would honor the late glaciologist Stan Paterson, who helped reconstruct climate data for the past 100,000 years using ice cores from Greenland.

“The possibility of additional subglacial craters beneath the Greenland and Antarctic ice sheets should be investigated, as our discovery further emphasizes the ability of ice sheets to both bury and preserve evidence of terrestrial impacts,” the team said.