Grand Canyons on the Moon Were Made in a Matter of Minutes

Two canyons near the south pole of the moon rival the Grand Canyon, both in depth and length.Unlike the sinuous chasm in Arizona, the two lunar canyons, known as Vallis Schrödinger and Vallis Planck, are straight, as if the crust of the moon had been cut by a knife.And unlike the Grand Canyon, carved over millions years by the flow of the Colorado River, Vallis Schrödinger and Vallis Planck formed in just minutes after a 15-mile-wide meteor struck the moon some 3.8 billion years ago.Indeed, carving these vast lunar trenches took less time than it might take you to bake a frozen pizza.The impact, comparable to the one that smashed into the Earth 66 million years ago and killed the dinosaurs, punched up to 15 miles into the crust and excavated a crater about 200 miles wide. In the process, it ejected fusillades of giant rocks — what planetary scientists call ejecta rays — that crashed down in staccato succession to create the canyons, which are more than 1.5 miles deep and more than 165 miles long.“They truly are extraordinary in scale,” said David Kring, a scientist at the Lunar and Planetary Institute in Houston. “These things were carved in less than 10 minutes when the Grand Canyon took 5 to 6 million years to carve. I mean that illustrates the energy of an impact event.”In a new analysis, Dr. Kring and his colleagues, Danielle Kallenborn and Gareth Collins of Imperial College London, constructed a mathematical model to describe how the canyons formed in a rain of giant rocks. They used photographs taken by NASA’s Lunar Reconnaissance Orbiter, which showed a string of craters along the canyons, to calculate the speed and direction of the debris.“Imagine a kilometer- or a five-kilometer rock hitting the ground at over 2,000 miles per hour,” Dr. Kring said. “Each one of these blocks will produce a crater about 20 kilometers in diameter. And they hit the ground — bang, bang, bang, bang, bang.”The scientists calculated that the energy needed to create the two canyons was more than 130 times what would be produced in an explosion of all the nuclear weapons that exist on Earth today.Their findings appear in a paper published on Tuesday in the journal Nature Communications.The canyons also suggest that the incoming asteroid or comet hit at an angle even though the crater itself is almost circular in shape.The straight lines of Vallis Schrödinger and Vallis Planck radiate outward from the Schrödinger basin crater. But the scientists noticed that the lines, if extended, did not intersect at the center of the crater.Instead, the intersection point is to the south. That is likely where the space rock hit, the scientists said.“I think they’ve got the interpretation right on that,” said Jennifer Anderson, a professor of geoscience at Winona State University in Minnesota. “These ginormous crater rays, they point back to a point that is up range of the center of the crater.”That indicates that the meteor came from the south and that the curtain of debris was largely kicked to the north, away from the south pole.That is an encouraging finding for Artemis, NASA’s return-to-the-moon program, because it suggests that the areas near the south pole where the agency wants to land astronauts are not covered by debris from the Schrödinger impact and that rocks from a much larger, much older impact known as the South Pole–Aitken basin would be exposed at the surface.Dr. Anderson said the new findings matched with small-scale laboratory experiments she had conducted a couple of decades ago, firing BB-size pellets into sand, which created craters less than a foot in diameter.“It’s the farthest ejecta on the surface that tell you about what happened at earliest times in the cratering event,” she said.What is less certain is how the impact produced a long, narrow stream of rocks in the ejecta rays instead of a more uniform cascade in all directions.“We still debate the origin,” Dr. Kring said.The ejecta rays might have resulted from earlier craters or other unevenness of the terrain. “It could have been two preexisting craters caused the focusing of some of this debris into these rays,” Dr. Kring said.Dr. Anderson said such rays also occurred in her small-scale experiments, and she, too, could not explain that phenomenon.“We can see that there are areas of the ejecta curtain that are more dense with material as opposed to less dense,” she said. “Why that is, I don’t know that anyone knows yet, except that nature is messy.”