The Moon has a Canada-sized crater, and researchers are thrilled by their discovery

New research published in the journal Earth and Planetary Science Letters suggests that the Moon's oldest and largest impact crater, the South Pole-Aitken Basin, may be more circular than previously believed. For many years, scientists thought the basin had an elongated, elliptical shape. However, a team of scientists from the University of Maryland presented the results of a new analysis indicating that the collision which formed the basin occurred at a more vertical angle, resulting in a rounder shape.

The South Pole-Aitken Basin is considered the largest and oldest known impact structure on the Moon, with dimensions of 2,400 by 2,050 kilometers and a depth reaching 8 kilometers. It is located on the far side of the Moon and was first photographed by the Soviet spacecraft Luna 3 in 1959, and later by NASA's Clementine spacecraft in 1996. Its age is estimated to be more than 4 billion years, and many other impacts have obscured its original appearance.

"It's challenging to study the South Pole-Aitken Basin holistically due to its sheer enormousness, which is why scientists are still trying to learn its shape and size," said Assistant research scientist Hannes Bernhardt, who led the study. The team re-examined the basin and determined it has a more rounded shape than previously thought, as reported by Space.com.

The researchers reached this conclusion by studying data from the Lunar Reconnaissance Orbiter, which provided insights into the distribution of materials resulting from the impact. They used the data to find and analyze more than 200 mountain-shaped formations scattered around the basin. The shape of these formations and their distances from one another signify a more rounded crater that would be created from a vertical impact.

"The rounded shape implies that the debris from the impact are distributed around the point of impact more evenly than was originally assumed," the researchers stated. According to Bernhardt, this means "Artemis astronauts or robots in the South Pole region may be able to closely study rocks from deep within the Moon's mantle or crust—materials that are typically impossible for us to access." Bernhardt is cited by Space.com.

This new understanding challenges previous theories. For many years, it was believed that the South Pole-Aitken Basin had an oval or elliptical shape. Based on this, studies established that the crater was formed by an object striking the Moon at a shallow angle, with scientists comparing the event to a stone skipping on water. The prevailing theory suggested that the collision resulted in relatively few fragments being scattered around the South Pole of the Moon.

The new findings suggest that the impact was more vertical, "possibly similar to dropping a rock straight down onto the ground," Bernhardt said. "Our results may play a key role in understanding the evolution of the Moon," he added.

Recent data from the Indian spacecraft Chandrayaan-3 discovered minerals presumably related to mantle materials near the Moon's South Pole, which also agrees with the theory of a vertical impact, as reported by Gazeta.ru.

NASA plans to send astronauts close to the Moon's south pole again as part of the Artemis missions. Artemis 2, the first mission of its kind since 1972, is set to bring astronauts to the lunar surface in April 2026, according to Space.com. The new findings may have significant implications for these missions, as astronauts or robots may be able to study materials from deep within the Moon's mantle or crust.

Previous research published in October in Nature Astronomy dated the South Pole-Aitken Basin to between 4.32 and 4.33 billion years old. In that study, researchers determined the basin's age by dating uranium and lead found inside the Northwest Africa 2995 lunar meteorite, discovered in Algeria in 2005, as reported by Space.com.

This article was written in collaboration with generative AI company Alchemiq