The far side of the moon has its own versions of the Grand Canyon — two of them, in fact!
A new study published in Nature Communications explains how these deep canyons formed very quickly during an asteroid impact. KNAU’s Melissa Sevigny spoke with Flagstaff planetary scientist David Kring of the Lunar and Planetary Institute about the findings.
MELISSA SEVIGNY, KNAU: What made you want to study how these canyons were formed?
DAVID KRING: Before the current Artemis program there was a Constellation program… and NASA when to the National Academy of Sciences and said: what are our national priorities if we go back to the moon?... And as it turned out the Schrödinger impact basin, which is on the far side of the moon, hidden from our view, was the best place to do the most science. For the last 15 years, we’ve been studying the Schrödinger impact basin… Recently, we turned our attention to the debris that was ejected from the basin, and that led us to take a closer look at these two canyons.
KNAU: So this is an impact basin on the far side of the moon, it’s got these two canyons, they look like rays radiating out from it, what did you find about how they were formed?
DK: We’ve determined that an asteroid roughly 25 kilometers in diameter hit the lunar surface about 3.8 billion years ago, and in the process of excavating that basin it threw up a curtain of debris, and within that curtain of debris were two streams of rock…. And that material arched over the lunar surface and then came crashing back down. It produced a series of impact craters in a staccato fashion — boom, boom, boom, boom. These were huge craters, so 1,000 times bigger than our own Meteor Crater just down the road. Collectively all of those impact craters formed these long, linear, radial canyons.
KNAU: I remember in the paper, you showed side-by-side what they looked like compared to the Grand Canyon. Tell me about that.
DK: Everybody’s familiar with the Grand Canyon, our beloved Grand Canyon. It’s roughly, if you go along the Bright Angel Trail, about 25 kilometers across. Our canyons are similar, they’re 20 to 27 kilometers across. They’re a little bit deeper, they’re 2.7 to 2.5 kilometers deep. Boy, would that would be a hike! And so they’re just enormous. One of the things our calculations showed was that they are produced very quickly. We all know the story of the Grand Canyon taking millions of years to carve… whereas in this impact cratering process, these canyons were excavated in minutes.
KNAU: I’m curious, a lot of people know what it’s like to hike from the rim to the river in the Grand Canyon. If you were standing on the moon, what would it be like to hike these canyons?
DK: The topography on the lunar surface is smoother, with the exception of craters. There’s an ongoing bombardment by smaller asteroids and comets all the time. You’re constantly walking in and out of small craters. But with that exception, it’s a smooth—a more open canyon. If you were standing on the rim… you could look down the length of this canyon from the rim, not something you can do with our Grand Canyon.
KNAU: What you makes you so excited to study these kinds of processes, you know, impact craters and things smashing into other things?
DK: First of all this landscape. Imagine — these canyons are the size of the Grand Canyon! And by the way, they’re not too far from mountain summits that dwarf Mount Everest. The landscape on the lunar south polar region, and on the far side, is just extraordinary. I tell people, if it was on the Earth, these would be national or international parks. …. But also it’s that downstream look, an opportunity to explore that region of the moon and begin piecing together the earliest history of the moon. People will say, why do we need to study the moon? I point out to people that when we’re studying these earliest epochs of the moon, we are in effect studying the earliest epoch of Earth, which has been erased. If you really want to understand what happened in the first 5-6-700 million years of Earth's history, you have no other choice but to go to the moon. It’s fun to go to the moon and understand and appreciate that you’re also getting a better understanding of home.
KNAU: That’s lovely, I really like that. David Kring, thank you so much for speaking with me today.
DK: My pleasure.
