Asteroid impact on Moon carved massive canyons within minutes
Analysis of lunar photographs details ancient strike, provides optimism for future lunar missions
When a massive asteroid slammed into the Moon’s southern region 3.8 billion years ago, it shot out debris that—with energy 130 times greater than Earth’s entire nuclear arsenal—carved lunar fissures comparable in size to the Grand Canyon within minutes. The finding, reported today in Nature Communications, doesn’t just illuminate a cataclysmic bit of lunar history—it may have cleared up a concern for future NASA missions.
The results indicate the spray of debris kicked up by the asteroid likely spared the exploration zone where astronauts plan to collect and date debris fragments from an even older impact. Such missions could answer questions about the Moon’s earliest history and perhaps even the story of how life took root on Earth.
The finding is “very important,” says Georgiana Kramer, a planetary scientist at the Planetary Science Institute who was not involved with the work. It provides some reassurance to the astronauts of NASA’s Artemis mission that their sample collection won’t be contaminated with the younger asteroid impact debris, she says.
Artemis astronauts are scheduled to take off for the Moon’s surface in 2027. NASA plans to send them to the south pole, where they will collect rocks from the South Pole–Aitken Basin, the largest and oldest visible basin on the Moon. The 2500-kilometer-wide basin is shallow but immense, and the Artemis team’s exploration zone will be littered with rocks dredged up during its formation from a massive asteroid strike.
The Moon’s surface is scarred by many basins and craters. The younger they are, the smaller they tend to be, notes Jacob Bleacher, chief exploration scientist for a NASA directorate helping plan the future Artemis lunar missions. This trend reflects the disappearance of the massive asteroids that once whizzed through our early Solar System, slamming into young planets and perhaps periodically snuffing out nascent life on Earth. As the number of these enormous rocks in our Solar System decreased, life on Earth finally had a chance to gain “a foothold,” Bleacher says.
The South Pole–Aitken Basin in theory represents the oldest record of the most massive impacts in the Earth-Moon system. Determining the basin’s age would tell scientists how long ago the Solar System’s planets were still experiencing life-snuffing asteroid strikes. In short, its age would likely reflect an upper bound on when life on Earth started to become sustainable.
“The lunar surface is basically like a time stamp of the very early history of our solar system,” says study co-author Danielle Kallenborn, a planetary scientist at Imperial College London.
The problem is that scientists have yet to definitively nail down the South Pole–Aitken Basin’s age. By collecting rocks from the basin’s inception, they hope to update the current estimates, about 4.3 billion years.
But sitting inside of the South Pole–Aitken Basin, just north of the Artemis mission’s planned landing site, is the much smaller Schrödinger Basin, the second youngest of the Moon’s great basins at an estimated 3.8 billion years old. The later asteroid that excavated the Schrödinger Basin could have easily sprayed debris over the Artemis exploration zone, complicating efforts to date the underlying South Pole–Aitken Basin rock.
So, Kallenborn and colleagues mathematically re-enacted the minutes after a 25-kilometer-wide asteroid carved out the Schrödinger Basin. The scientists analyzed photographs and surface height measurements collected by NASA’s Lunar Reconnaissance Orbiter, launched in 2009. They determined where exactly the asteroid must have landed and its angle of descent for the ejected debris to carve two canyons that run in straight lines away from the Schrödinger Basin’s rim, making the depression look like a hand forming the peace sign.
These canyons—“as wide, and deeper than, the Grand Canyon on Earth”—were formed when the debris excavated rows of smaller craters that overlapped or collapsed into each other, says study co-author David Kring, a planetary scientist at the Lunar and Planetary Institute. The team was even able to calculate the size and velocity of the debris fragments that gouged the canyons’ individual craters.
“Just a bit of maths basically,” Kallenborn says.
The team’s calculations suggest the asteroid flew over the south pole at a shallow angle before hitting the ground, plowing northward and spraying debris in front of it, away from the planned Artemis exploration zone. That’s good, Kramer notes. “We want to be sampling South Pole–Aitken ejecta or even pristine crust,” she says.
The Moon rocks astronauts intend to collect from the dead lunar surface are the best substitute for fragments of Earth’s own catastrophic collisions with asteroids. Weather, water, and geological activity on Earth have ground any remnants of those catastrophes into “mineral relics,” Kring says.
The lunar surface holds the evidence for when life on Earth became a long-term prospect, Bleacher says. “The Moon has been sitting there with us pretty much for the whole history of the Earth, just recording what’s happened.”
