Unveiling the Grand Canyons of the Moon
Two Immense Canyons Discovered on the Far Side of the Moon
In a significant discovery, a team of scientists at the Lunar and Planetary Institute (LPI), an institute of the Universities Space Research Association (USRA), found that two immense canyons hidden in the lunar far side are similar in width and depth to the Earth's Grand Canyon. The findings were published last week in Nature Communications.
"While the Grand Canyon took millions of years to form, the two grand canyons on the Moon were carved in less than 10 minutes."
David Kring, USRA
The two extraordinary features were produced during a period of planetary upheaval when the Earth and Moon were being resurfaced by impacting asteroids and comets. "Nearly four billion years ago," explains lead author David Kring (USRA), "an asteroid or comet flew over the lunar south pole, brushed by the mountain summits of Malapert and Mouton, and hit the lunar surface. The impact ejected high-energy streams of rock that carved two canyons that are the size of Earth's Grand Canyon. While the Grand Canyon took millions of years to form, the two grand canyons on the Moon were carved in less than 10 minutes."
The impacting asteroid or comet likely hit the lunar surface with a speed of nearly 55,000 kilometers per hour (35,000 miles per hour). The impact produced the enormous 320-kilometer-diameter Schrödinger impact basin and propelled the rocky debris that scoured the deep grooves into the lunar surface.
The investigation began in Houston where second author Danielle Kallenborn was conducting an undergraduate student internship with Kring at USRA's LPI and also engaged impact cratering specialist Gareth Collins at Imperial College London where Kallenborn is now conducting doctoral thesis studies. Probing the distant past when impact bombardment was reshaping the Moon captivated Kallenborn: "Analyzing the Schrödinger impact event showed me what a fascinating research target the Moon is. The lunar surface is like a timestamp of the early times of our solar system."
The authors analyzed the canyons using images and elevation data from NASA's Lunar Reconnaissance Orbiter spacecraft. Those measurements indicate the canyons are 20 to 27 kilometers wide, 2.7 to 3.5 kilometers deep, and 270 to 860 kilometers long. The features are called Vallis Schrödinger and Vallis Planck.
The authors calculated the ballistic flight of ejected debris that created the canyons. After flying over the lunar surface, the debris hit the lunar surface at speeds of about 1 kilometer per second (3600 kilometers per hour or 2237 miles per hour). The debris produced rays of secondary impact craters that form the canyons.
"The Schrödinger crater is similar in many regards to the dino-killing Chicxulub crater on Earth," said co-author Gareth Collins. "By showing how Schrödinger's km-deep canyons were carved, this work has helped to illuminate how energetic the ejecta from these impacts can be."
The energy to produce the grand canyons on the Moon is about 130 times larger than the energy in the global inventory of nuclear weapons.
Most of the excavated rock was ejected away from the lunar south polar region, which Artemis astronauts will soon explore. Because the Schrödinger impact debris did not bury the lunar south polar region, astronauts will find it easier to collect geologic samples from an even older epoch in lunar history. Moreover, the two canyons provide an extraordinary opportunity to sample material that is more ancient and once lay two or three kilometers beneath the lunar surface.
That extraordinary geology will be matched by extraordinary vistas. "The splendor of the canyons is so dramatic that if exposed on Earth, they would be national or international parks," Dr. Kring said.