Retherford, Kurt - Lunar Volatile Transport in the Exosphere and from Impact Plumes: LRO/LAMP Observing Campaigns Coordinated with LADEE

Abstract: 
The Lyman Alpha Mapping Project (LAMP) is an ultraviolet (UV) spectrograph on the Lunar Reconnaissance Orbiter (LRO) that maps the lunar albedo and investigates the lunar exosphere at far-UV wavelengths.  Lunar helium atmospheric emissions have been detected remotely with LAMP (Stern et al. 2012), enabling global investigations of its distribution and variability. Helium studies show the abundance varies with solar wind conditions (as expected), including stoppages of helium in-flux during Earth magnetotail transits (Feldman et al. 2012) and a few interesting cases of rapid helium abundance increases (Cook & Stern 2014).  LCROSS impact plume observations with LAMP detected H2, CO, Hg, Mg, and Ca (Gladstone et al. 2010), which together with LCROSS observations revealed a much richer mix of volatiles trapped within the PSRs than previously anticipated.  GRAIL spacecraft impact plume observations with LAMP detected H and Hg at a high latitude sunlit region (Retherford et al., LPSC, 2013).  LAMP's lightcurves of the time evolution of these emissions provide useful constraints to detailed gas plume dynamics models for such impacts reported by Hurley et al. 2012.  Tentative detections of argon gas just nightward of the dusk terminator (Cook et al., LPSC, 2014) have a latitudinal distribution that agrees well with model simulations (Grava et al., submitted to Icarus, 2014).  Molecular hydrogen is also detected with LAMP (Stern et al. 2013).  New, more constraining upper limits to 27 other potential atmosphere constituents have been determined using LAMP (Cook et al. 2013). Lunar Atmospheric and Dust Environment (LADEE) Neutral Mass Spectrometer instrument measures in situ He, Ar, and Ne (Benna et al., LPSC, 2014).  The LADEE Ultraviolet-Visible Spectrometer (UVS) routinely measures Na and K emissions, and additionally searches for exospheric dust signatures (Colaprete et al., LPSC, 2014). LAMP searches for similar exospheric dust signatures from dust scattered sunlight and found that upper limits for lunar horizon glow during these observations were at least two orders of magnitude smaller than that inferred from coronal photographs taken during the Apollo 15 mission (Feldman et al. 2014).  LADEE's Lunar Dust Experiment (LDEX) occasionally observes bursts of dust particles that are seemingly related to individual meteoroid impacts, but like LAMP, has not detected persistent clouds of fine-grained exospheric dust (Horanyi et al., LPSC, 2014).  Analysis of LAMP observations obtained during a series of campaigns coordinated with the LADEE mission is currently underway, and we will present our latest findings.  LAMP's view of twilight local time regions from LRO's polar orbit, when combined with LADEE's low (<22.5° N/S) latitude retrograde orbit and instrument set, provides a new global perspective on the lunar exosphere that promises to improve our understanding of volatile and dust transport processes.