The effect on the lunar exosphere of a coronal mass ejection passage

Solar wind bombardment onto exposed surfaces in the solar system produces an energetic component to the exospheres about those bodies. The solar wind energy and composition are highly dependent on the origin of the plasma. Therefore, using the measured composition of the slow wind, fast wind, solar energetic particle (SEP) population, and coronal mass ejection (CME), we have estimated the total sputter yield for each type of solar wind. We show that the heavy ions, especially the He++ and O+7, can greatly enhance the total sputter yield during times when the heavy ion population is enhanced. Folding in the flux with the yield of individual ions, we compute the source rate for several species during different types of solar wind. Finally, we use a Monte Carlo model developed to simulate the time-dependent evolution of the lunar exosphere to study the sputtering component of the exosphere under the influence of a CME passage. We simulate the background exosphere of Na, K, Ca, and Mg. Simulations indicate that sputtering increases the mass of those constituents in the exosphere more than ten times the background values. The escalation of atmospheric density occurs within an hour of onset. The decrease in atmospheric density after the CME passage is also rapid, although takes longer than the increase. Sputtered neutral particles have a high probability of escaping the Moon, by both leaving the Hill Sphere and photoionization. Density and spatial distribution of the exosphere can be tested with the LADEE mission.