New research shows that when an asteroid slammed into the Moon billions of years ago, it carved out a pair of grand canyons on its far side.
The development is good news for scientists and NASA, which is looking to land astronauts at the south pole on the near, Earth-facing side of the Moon, untouched by the impact and containing older rocks in original condition.
US and British scientists used photos and data from NASA's Lunar Reconnaissance Orbiter to map the area and calculate the path of debris that produced these canyons about 3.8 billion years ago.
They reported their findings in the journal Nature Communications.
The incoming space rock passed over the lunar south pole before it struck, creating a huge basin and sending streams of boulders hurtling at a speed of nearly one mile a second.
The debris landed like missiles, digging out two canyons comparable in size to Arizona’s Grand Canyon in barely 10 minutes.
The latter, by comparison, took millions of years to form.
"This was a very violent, a very dramatic geologic process," said lead author David Kring of the Lunar and Planetary Institute in Houston, Texas.
He and his team estimate the asteroid was 24km across and that the energy needed to create the two canyons would have been more than 130 times that in the world’s current inventory of nuclear weapons.
Most of the ejected debris was thrown in a direction away from the south pole, Mr Kring said.
That means NASA’s targeted exploration zone around the pole mostly on the Moon’s near side will not be buried under debris, keeping older rocks from four billion plus years ago exposed for collection by moonwalkers.
These older rocks can help shed light not only on the moon’s origins, but also Earth’s.
Mr Kring said it is unclear whether the two canyons are permanently shadowed, like some of the craters at the south pole, adding "that is something that we’re clearly going to be re-examining".
Permanently shadowed areas at the bottom of the Moon are thought to hold considerable ice, which could be turned into rocket fuel and drinking water by future moonwalkers.
NASA’s Artemis programme, the successor to Apollo, aims to return astronauts to the lunar surface this decade.
The plan is to send them around the Moon next year, followed a year or so later by the first touchdown by astronauts since the Apollo mission.
