The moon may have far more lunar craters than previously known

Moon craters formed when meteorites and asteroids slammed into the lunar surface. Like fossils on Earth, they reveal something about the history of the solar system and how planets were formed.

Using artificial intelligence, Chinese scientists have estimated that there are more than 100,000 craters on the moon, according to a study published Tuesday in the journal Nature Communications. That’s far more than the 9,137 officially recognized by the International Astronomical Union and largely detected manually using elevation information and images, the study said.

The scientists, using data on 7,895 previously identified craters and 1,411 dated craters, were able to apply machine learning to train a deep neural network. With information from China’s first and second lunar orbiters — Chang’e 1 and Chang’e 2 — the network identified 109,956 new craters. The two unmanned spacecraft launched in 2007 and 2010, respectively.

“Impact craters (are) the most diagnostic features of the lunar surface. That is in great contrast to the surface of the Earth. It is very difficult to trace the Earth’s history of being impacted by asteroids and comets over the past 4 billion years,” said study author Chen Yang, of the College of Earth Sciences at Jilin University and the Key Laboratory of Lunar and Deep Space Exploration at the Chinese Academy of Sciences.

“Earth and the moon have been struck by the same impactor population over time, but large lunar craters have experienced limited degradation over billions of years. Therefore, lunar impact craters can trace the evolution of the Earth,” she said via email.

The craters on the moon lack water, an atmosphere and tectonic plate activity — three forces that erode the Earth’s surface, meaning that all but the most recent meteor impacts aren’t visible.

On the moon, however, pretty much any dent isn’t going anywhere. The dusty footsteps of astronauts who walked on the moon during the Apollo missions are still there today.

According to the Lunar Planetary Institute, approximately 80% of Earth’s surface is less than 200 million years old, while over 99% of the moon’s surface is more than 3 billion years old. The age of a large crater can also be determined by counting how many small craters are found inside it.

This latest study isn’t the first to deploy machine learning to detect lunar craters, said Mohamad Ali-Dib at the Institute for Research on Exoplanets at the University of Montreal.

He was part of a team at the University of Toronto Scarborough that used data from a laser altimeter, a device used aboard planet-orbiting satellites to map terrain, rather than optical images used by the Chinese team, to detect craters. The UT team identified about 6,000 previously unidentified craters on the moon in research published in 2018.

“Machine learning can be used to detect craters on the moon,” he said via email. Craters are “a window into the dynamical history of the solar system.

China became only the third country in the world to successfully collect rocks from the moon when in mid-December the unmanned Chang’e-5 mission returned to Earth carrying the country’s first moon samples.