10,000 Lunar Faults Reveal 45-Meter Shrinkage Over Millions of Years

The Moon is shrinking, and researchers are narrowing down the extent of this contraction that has occurred over millions of years. The natural satellite is believed to have formed from a violent collision between a massive body and the early Earth approximately 4.5 billion years ago. Since that impact, the lunar interior has been gradually cooling. As temperatures continue to drop, the Moon contracts, driving a slow shrinkage process across geological time. A new study suggests scientists have now determined the magnitude of this volume reduction.

Lunar Reconnaissance Orbiter Camera Data

According to Space.com, scientists analyzed images captured by the Lunar Reconnaissance Orbiter Camera (LROC) and identified more than 10,000 relatively recent faults on the lunar surface. This observation helped quantify the Moon’s shrinkage over time. Researchers now estimate that the Moon’s radius has decreased by approximately 148 feet, or 45 meters, during the period spanning the last 400 to 800 million years.

Thomas Watters, the study’s lead researcher and a geologist and curator at the Smithsonian Institution’s National Air and Space Museum Center for Earth and Planetary Studies, stated in a release: “The number of these young faults revealed by LROC images is much larger than I imagined.” He added that as the lunar interior continues to cool and contract, existing faults are expected to grow, and new ones will form even today.

Diverse Geological Formations Identified

LROC observations revealed various types of faults and terrain features on the Moon. These include lobate scarps, which are long, curved structures that form when the lunar surface shrinks, cracks, and pushes layers upward. The data also showed small ridges within lunar maria, appearing as narrow wrinkles on the dark plains extending across the surface. These geological formations assist scientists in understanding how the Moon’s surface changes due to internal cooling and subsequent contraction over time.

Tectonic Differences Between Earth and Moon

Lunar tectonic activity differs significantly from that of Earth. Our planet contains roughly 15 major tectonic plates, whereas the Moon has none. Instead, the Moon consists of a single-plate outer shell, meaning its crust represents one solid mass interspersed with faults and fractures resulting from contraction. Consequently, lunar faults do not concentrate at plate boundaries as they do on Earth; rather, they spread across different regions of the lunar surface.

Crust Thickness and Regional Stability

By mapping thousands of geological formations created by the Moon’s cooling and shrinking history, researchers aim to reconstruct its geological timeline. Beyond determining the amount of shrinkage, the team found that some regions contain far more faults than others. Areas with fewer fractures feature thicker lunar crust. Scientists concluded that regions with thicker crust exhibit greater stability. Results indicate that many of the widespread cracks on the surface formed during relatively late stages of the Moon’s history. In earlier phases, the thick crust likely insulated the warm interior, slowing heat loss, contraction, and fracturing until these processes continued over time.