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  • Temperature of four grains each with different initial radius. These plots used the updated energy balance equation applied to the updated LCROSS code.
  • Sample run showing the optical depth of the plume as seen from the lunar south pole.
  • Radiance vs time plot for LCROSS plume
  • Radius plot for multiple LCROSS simulations. The Color Lines show a two species simulation with two grain species: pure ice and pure dirt. The different colors indicate the fraction of total ice mass that is initially in the spike component of the plume. The black line shows a one species simulation with one grain species: pure dirt core with a thin ice coating.
  • This is a schematic drawing of the LCROSS plume. The Shepherding Spacraft is labeled “S-S/C” on the top of the diagram. The spike and cone components of the plume are labeled as such. δ_s and δ_c are the spike and cone angles with respect to the vertical.
  • Diagram of some of the regolith physics included in the model

In 2009, the Lunar Crater Observation and Sensing Satellite (LCROSS) impacted the Moon to determine the existence of water ice in permanently shadowed lunar craters. The upper stage of the satellite struck the Cabeus crater near the lunar south pole, creating a large plume. The satellite flew through that plume collecting data before striking the Moon as well. Here at UT we are modeling the impact using a free molecular dynamics code to model the evolution of the plume. The code tracks the lunar ice covered regolith grains as they undergo radiative heat transfer and sublimate their water in the sunlight. Ionization and photo-dissociation of the water is also modeled, as well as “thermal hopping” due to adsorbtion and re-emission from the lunar surface. The spectral radiance of the plume as detected by the SSC as it descended is computed by using a single-scattering approximation.

Current work includes modeling additional physics of the regolith grains, incorporating separate pure regolith and pure ice species, adding dirty ice grains with variable ice to regolith ratios, modeling plume opacity as a function of wavelength, and generating spectra along lines of sight. These improvements will allow us to better understand the properties of the ice and dust particles and their interactions within the plume. This knowledge will help to assess conditions within permanently shadowed regions on the Moon.