A vast impact crater near the moon鈥檚 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.
at the Lunar and Planetary Institute in Houston, Texas, has researched the 312-kilometre-wide Schr枚dinger crater for 15 years. Part of that was to develop possible landing sites for NASA鈥檚 Constellation programme 鈥� which sought to return people to the moon but was ended in 2009. The canyons radiating from it have long fascinated him.
鈥淭hey鈥檙e basically hidden, in some sense mysterious, because they鈥檙e on the far side [of the moon],鈥� says Kring. 鈥淎nd so they鈥檙e commonly overlooked.鈥�
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To learn more, Kring and his colleagues have now used computer models to investigate the origin of two canyons, or 鈥渞ays鈥�, that extend northwards from the crater. One is Vallis Schr枚dinger, 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鈥檚 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.
鈥淵ou have rock that鈥檚 hitting at a kilometre per second, maybe 2 kilometres per second, and that can be devastating,鈥� says Kring. 鈥淲e knew that the Schr枚dinger impact produced these rays, but the processes involved鈥� needed some detailed attention.鈥�
Kring says the findings will be reassuring for NASA鈥檚 Artemis III mission to put astronauts on the moon in the region of the south pole, as the ejected regolith from Schr枚dinger won鈥檛 be deep enough in any of the proposed landing spots to seriously hamper geology experiments. If they had been planning to land north of Schr枚dinger, where far more material landed, then they would have faced an extremely deep layer that masked earlier geology.
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.
鈥淭he ultimate proof would be someone bringing back a rock from one of these canyons, or some rocks,鈥� says Burchell. 鈥淭hen 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.鈥�
Nature Communications
