Grand canyons formed on moon in minutes after colossal asteroid strike

A vast impact crater near the moon’s south pole was formed by an asteroid moving at more than a kilometre a second, releasing energy when it struck equivalent to 130 times that of all the nuclear weapons in existence. Now, researchers say two unusually narrow and straight canyons that splay out from its centre were formed in less than 10 minutes by a chain of secondary debris impacts.

David Kring at the Lunar and Planetary Institute in Houston, Texas, has researched the 312-kilometre-wide Schrödinger crater for 15 years. Part of that was to develop possible landing sites for NASA’s Constellation programme – which sought to return people to the moon but was ended in 2009. The canyons radiating from it have long fascinated him.

“They’re basically hidden, in some sense mysterious, because they’re on the far side [of the moon],” says Kring. “And so they’re commonly overlooked.”

To learn more, Kring and his colleagues have now used computer models to investigate the origin of two canyons, or “rays”, that extend northwards from the crater. One is Vallis Schrödinger, which is 270 kilometres long and 2.7 km deep, while the second, Vallis Planck, is 280 km long and 3.5 km deep. For comparison, the Grand Canyon in Arizona is 446 km long and up to 1.9 km deep.

But while that was carved by water over millions of years, the lunar canyons are clear, straight grooves formed by vast impact forces in less than 10 minutes, says Kring. The dramatic asteroid strike would have spread dust and rubble over the whole of the moon’s surface, but also into space and onto Earth.

The researchers suggest that it would also have driven debris across the lunar surface fast enough to cause craters outside the main one, and these could have been focused into narrow regions by irregularities in the regolith, the loose material that coats the moon.

With their models, the researchers calculated that an asteroid impact an estimated 3.81 billion years ago would have been capable of creating the required speed and direction of debris to create the canyons.

“You have rock that’s hitting at a kilometre per second, maybe 2 kilometres per second, and that can be devastating,” says Kring. “We knew that the Schrödinger impact produced these rays, but the processes involved… needed some detailed attention.”

Kring says the findings will be reassuring for NASA’s Artemis III mission to put astronauts on the moon in the region of the south pole, as the ejected regolith from Schrödinger won’t be deep enough in any of the proposed landing spots to seriously hamper geology experiments. If they had been planning to land north of Schrödinger, where far more material landed, then they would have faced an extremely deep layer that masked earlier geology.

Mark Burchell at the University of Kent, UK, says the research goes some way to prove that the canyons are formed by chains of impacts, but doing so for sure would require up-close investigation.

“The ultimate proof would be someone bringing back a rock from one of these canyons, or some rocks,” says Burchell. “Then you just cut them up and there will be grains of minerals in there which have been shocked [by impacts], and some of them have changed their structure as a result.”

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