Apollo 11 sample tray. Southwest Research Institute collaborated with UT San Antonio to analyze lunar soil samples and determine the effects of space weathering on their far-ultraviolet reflectance. SwRI measured the reflectance of the Apollo 11 soil sample in SwRI’s Slater Crater ultra-high vacuum instrument suite. Weathering increases the abundance of nanophase iron inclusions on the grain rims shown in these TEM images, which is primarily responsible for its darker ultraviolet reflectance. Credit: Southwest Research Institute

Southwest Research Institute (SwRI) scientists are collaborating with researchers at UT San Antonio to study how space weathering can alter the lunar surface materials to help interpret regional and global far-ultraviolet (FUV) maps of the moon.

Their recent study looked at how such weathering influences the FUV spectral response. By analyzing just a few grains of returned samples from the Apollo missions, the team gained important insights into the evolution of the lunar surface shaped by solar wind and micrometeoroid impacts over eons, said SwRI’s Dr. Ujjwal Raut.

The paper is published in the Journal of Geophysical Research: Planets.

Using modern instruments and investigative techniques, the team gleaned new information from soil samples returned to Earth by NASA’s Apollo missions in the late ’60s and early ’70s (Apollo 11, 16 and 17).

"These Apollo-era samples continue to be a cornerstone of lunar science, providing the most direct link to the moon’s surface processes and evolution, including space weathering," Raut said.

The research was led by Caleb Gimar, who recently completed a doctoral degree in physics through the SwRI-UT San Antonio Joint Graduate Program, with support from NASA’s Lunar Data Analysis Program. Raut served as principal investigator of the project.

Apollo 11 grain rims. Credit: Southwest Research Institute

"We are investigating how space weathering drives physical and chemical changes in lunar grains that largely control their far-ultraviolet reflectance—explaining why soils with different degrees of weathering vary in brightness and the way they scatter light in this spectral region," Gimar said.

This is important because it allows researchers to better interpret remote sensing data from the Lunar Reconnaissance Orbiter Lyman-Alpha Mapping Project (LRO-LAMP), which has been orbiting the moon since 2009.

"The SwRI-led LAMP instrument was designed to search for signs of water ice by peering into the permanently shadowed polar craters using far-ultraviolet light from stars instead of the sun," said Dr. Kurt D. Retherford, principal investigator of the LAMP instrument.

"Accurately identifying that ice and estimating its abundance depends on understanding the far-ultraviolet reflectance of the dry lunar soil—while accounting for any mineralogical differences caused by space weathering—to robustly isolate hydration signatures from the soil itself."

This work highlights a close collaboration between SwRI’s Center for Laboratory Astrophysics and Space Science Experiments (CLASSE) and UT San Antonio’s Kleberg Advanced Microscopy Center (KAMC), which led the key nanoscale imaging of the lunar grains.

"We used a state-of-the-art transmission electron microscope—one that can actually image individual atoms," said Dr. Ana Stevanovic, KAMC director. "This microscope allows us to look deep inside individual grains of lunar dust and identify tiny minerals and space-weathering features while also measuring their chemical makeup."

The images revealed that the outer rims of the heavily weathered grains are studded with countless tiny particles of iron, known as nanophase iron, whose width is roughly one ten-thousandth that of a human hair, Stevanovic said. Less weathered grains contained far fewer of these nanophase iron inclusions, appearing brighter in the far-UV.

More information: C. J. Gimar et al, The Influence of Space Weathering on the Far‐Ultraviolet Reflectance of Apollo‐Era Soils, Journal of Geophysical Research: Planets (2025). DOI: 10.1029/2025je009304

Citation: Lunar soil analyses reveal how space weathering shapes the moon’s ultraviolet reflectance (2025, December 10) retrieved 10 December 2025 from https://phys.org/news/2025-12-lunar-soil-analyses-reveal-space.html

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