Sulfur Compositional Effects on Space Weathering

The reflectance spectrum of visible and near infrared light off of airless bodies in our Solar System gives us insight to surface mineralogy. However, this method of remote sensing is subjected to the space weathering effects of darkening and reddening optical spectra, along with changes to the depths of absorption bands over time. These optical changes are caused by nanophase iron blebs as a result of micrometeorite impacts and solar wind radiation. These two space weathering processes create melt and vapor deposits that coat mineral grains. The amount of vapor and melt is a function of mineral composition. We seek to understand the effects of sulfur on a refractory composition such as anorthosite, which is commonly found in the regolith of the moon’s highlands and possibly Mercury. X-ray spectrometry from the MESSENGER mission, Nittler (2011), returned a “sulfur abundance of up to ~4% weight in surface materials”. We will use sulfur compositions of 0%, 2%, 4%, and 8% weight in anorthosite samples. In line with NASA’s Strategic Goals of understanding processes and surface evolution of solar bodies, this experiment investigates the effects of sulfur composition on simulated space weathering of anorthosite. The results of this experiment show that the presence of sulfur in the Mercurian soil can contribute to 16% darker and 72% redder spectra; However, sulfur does not fully explain the 1.5 times lower in reflectance as compared to immature lunar highlands materials. Additional means are necessary (e.g., impact shock and melting) to explain the difference in brightness between the Moon and Mercury.