Latitudinal Variation in Spectral Properties of the Lunar Maria and Implications for Space Weathering

Abstract:

Space weathering alters the optical properties of exposed surfaces over time, complicating the interpretation of spectroscopic observations of airless bodies like asteroids, Mercury, and the Moon. Solar wind and micrometeoroids are likely the dominant agents of space weathering, but their relative contributions are not yet well understood. Based on Clementine reflectance mosaics and LOLA reflectance data, we report a systematic latitudinal variation in the near-infrared spectral properties of the lunar maria and show that the characteristics of this latitudinal trend match those observed at 'lunar swirls', where magnetic fields alter local solar wind flux without affecting the flux of micrometeoroids. We show that the observed latitudinal color variations are not artifacts of phase angle effects and cannot be accounted for by compositional variation alone. We propose that reduced solar wind flux, which should occur both at swirls and toward higher latitudes, is the common mechanism behind these color variations. This model helps us quantify the distinct effects of solar wind and micrometeoroid weathering and could aid in interpreting the spectra of airless bodies throughout the solar system.