Scientists have concluded that the Moon’s largest impact crater, the South Pole-Aitken basin, is much more circular in shape than previously thought. This has great implications for our understanding of the history of this celestial body.
The Moon’s largest crater
The South Pole-Aitken basin is the oldest and largest visible crater on the Moon, a massive 4 billion year old geologic wound that holds secrets about the Moon’s early history like a lunar time capsule.
Based on some features of the basin, researchers believed the crater was oval or elliptical in shape. For years, scientists believed this huge crater was formed by an object that hit the Moon at a low angle, possibly as extreme as a rock skipping over water. According to this theory, very little debris from the impact would have scattered across the Moon’s South Pole, which is the landing region for future Artemis missions that are supposed to return humans to the Moon’s surface.
But a new study led by the University of Maryland, published in the journal Earth and Planetary Science Letters, suggests that the impact may have been much more direct, resulting in a much more circular crater — a finding that challenges our current understanding of the moon’s history and has significant implications for future NASA missions to the Moon.
Complex basin shape
“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. In addition, 4 billion years have passed since the basin was originally formed and many other impacts have obscured its original appearance,” explained the study’s lead author Hannes Bernhardt, an assistant professor of geology at the University of Maryland.
Using high-resolution data from NASA’s Lunar Reconnaissance Orbiter, Bernhardt and his team have developed an innovative approach to understanding the complex structure of the South Pole-Aitken basin. They discovered and analyzed more than 200 rock formations scattered throughout the basin, geological features that the team believes are ancient remnants of the original impact.
Based on the distribution and shape of these rock elements, the team realized that the impact had to have created a more circular crater from which significant chunks of planet-forming material scattered across the Moon’s surface, including near the South Pole.
More circular shape
“A rounder, more circular shape indicates that an object struck the moon’s surface at a more vertical angle, possibly similar to dropping a rock straight down onto the ground,” Bernhardt said. “This circular impact implies that debris from the impact is more equally distributed around it than was originally thought, which means that 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.”
These lunar rocks could provide important information about the Moon’s chemical composition and help confirm theories about how the Moon may have formed from a massive collision between Earth and another planet-sized object.
Searching for collision debris
India’s Chandrayaan-3 lunar rover recently found minerals indicating collision debris coming from the mantle near the South Pole, supporting the UMD team’s theory of a more vertical impact with the formation of a circular basin that would be necessary to disperse such material in that area.
Bernhardt believes his team’s research provides critically important information for future missions to the Moon, helping mission planners and astronauts identify areas to explore and materials they may encounter. The thick layer, rich in materials from the lower crust and upper mantle, may offer unprecedented access to the Moon’s complex geologic history, potentially shedding light not only on the formation of the Moon, but also on the transformational events that shaped our Solar System.
Provided by phys.org
