SAN ANTONIO - Southwest Research Institute (SwRI) scientists working with researchers at UT San Antonio have analyzed Apollo lunar soil samples to determine how space weathering alters the Moon's surface and affects its far-ultraviolet (FUV) reflectance. The team examined how exposure to solar wind and micrometeoroid impacts over long periods changes the FUV spectral response of lunar grains, us Los Angeles CA (SPX) Dec 11, 2025
SAN ANTONIO - Southwest Research Institute (SwRI) scientists working with researchers at UT San Antonio have analyzed Apollo lunar soil samples to determine how space weathering alters the Moon's surface and affects its far-ultraviolet (FUV) reflectance. The team examined how exposure to solar wind and micrometeoroid impacts over long periods changes the FUV spectral response of lunar grains, using only a small number of particles from Apollo-era missions.
Using modern instruments and methods, the researchers re-examined soil returned by NASA's Apollo 11, 16 and 17 missions in the late 1960s and early 1970s. "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," said SwRI's Dr. Ujjwal Raut.
The project was led by Caleb Gimar, who recently completed a PhD in physics through the SwRI-UT San Antonio Joint Graduate Program with support from NASA's Lunar Data Analysis Program, with Raut serving as principal investigator. "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.
The findings help researchers interpret remote sensing data from the Lunar Reconnaissance Orbiter's Lyman-Alpha Mapping Project (LRO-LAMP), which has observed 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."
The work draws on SwRI's Center for Laboratory Astrophysics and Space Science Experiments (CLASSE) and UT San Antonio's Kleberg Advanced Microscopy Center (KAMC), which produced nanoscale images 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."
Imaging shows that heavily weathered grain rims contain many nanophase iron particles, each with a width roughly one ten-thousandth that of a human hair, according to Stevanovic. Less weathered grains contain far fewer of these nanophase iron inclusions and appear brighter in the far-ultraviolet, linking the abundance of nanophase iron to darker FUV reflectance in more weathered soils.
The results are reported in the Journal of Geophysical Research: Planets. The paper, titled "The Influence of Space Weathering on the Far-Ultraviolet Reflectance of Apollo-Era Soils," was published on December 3, 2025.
Research Report:The Influence of Space Weathering on the Far-Ultraviolet Reflectance of Apollo-Era Soils
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