We may think we know the face of the moon, but its mottled complexion still holds a few surprises.
Recently, a team of scientists found a new, 200-kilometer wide crater on the lunar nearside – a large pockmark that remained anonymous for billions of years.
To be fair, it’s mostly buried beneath material kicked out by an even bigger impact, said Rohan Sood, a graduate student at Purdue University who presented the observations March 16 at the Lunar and Planetary Science Conference.
“You’re probably the first person to discover a new, nearside crater in the last century or two,” Purdue’s Jay Melosh told Sood afterward.
The crater stayed hidden until NASA’s twin GRAIL spacecraft came along and mapped the moon’s gravity field. Small gravitational anomalies are associated with features, such as craters or mountains, that are normally visible on a body’s surface. But the shapes of those signatures can also reveal structures that our eyes can’t.
“Gravity is just more truthful, in a way,” says Loic Chappaz, another Purdue graduate student on the team.
When the team took a close look at the GRAIL gravity data, it spotted the signature of a large, buried crater. It wasn’t what they were expecting to find — “we were looking for buried, empty lava tubes,” Sood says – and the team realized they could use GRAIL data to search for hidden structures.
After verifying the crater’s presence, the team named it after Amelia Earhart, who was on faculty at Purdue before piloting a Purdue airplane on her last, fateful journey.
Earhart crater is located just north of Mare Serenitatis, a dark lunar basin that’s easily visible with the unaided eye. The crater, however, is not. When a massive impact formed the Serenitatis basin roughly 3.9 billion years ago, it kicked up enough material to mostly erase the slightly older Earhart crater.
“It threw out broken, melted rock and flooded the surface, several kilometers deep, and in the process removed the direct evidence of this older crater,” Melosh says.
Earhart crater is not alone in its clandestine existence. There are other similar craters, but many of them are truly buried. “There are maybe a dozen of those, something like that, that are clearly craters and we don’t see them on the surface,” Melosh says.