Elphic, Richard - Barnstorming the Moon: Adventures of the Lunar Atmosphere and Dust Environment Explorer

Abstract: 
The Lunar Atmosphere and Dust Environment Explorer (LADEE) was launched from Wallops Flight Facility on 6 September, 2013 aboard the very first Minotaur V, a Peacekeeper ICBM converted to civilian use.  The launch was perfect, and LADEE entered lunar orbit on 6 October, 2013.  In the following weeks, the first laser communications from deep space achieved 622 Mbits/sec downlink, paving the way for a revolution in space communications. Following instrument checkout and commissioning, LADEE commenced science operations on 21 November, 2013.  Over the next 100 days, LADEE's Ultraviolet/Visible Spectrometer (UVS) systematically mapped sodium, potassium and other species in the tenuous lunar exosphere, while the Neutral Mass Spectrometer (NMS) systematically mapped argon, helium, and discovered neon in the lunar exosphere.  At the same time, the Lunar Dust EXperiment (LDEX) discovered and characterized the dust exosphere, caused by continual bombardment of the Moon's surface by micrometeoroids.  After the nominal science mission, LADEE continued to acquire more science data, culminating in a set of observations at very low altitudes (<10 km) above the sunrise terminator.   Data from UVS show that the Moon’s sodium exosphere varies with lunar phase, with density increasing as the Moon waxes toward Full then falling after.  An additional wrinkle on this behavior is the apparent reduction in sodium while the Moon is in the Earth’s geomagnetic tail, suggesting that sodium production is diminished when out of the solar wind.  Potassium and other metals show variations on this behavior, including responses to meteoroid streams, particularly the Geminids.  NMS mapping of argon-40, a constituent arising from potassium-40 decay in the lunar interior, shows that the gas “freezes out” on the very cold lunar nightside (~100K), but produces a dawn bulge of enhanced density as the cold lunar surface rotates around into sunlight and warms up.  While this behavior was seen in Apollo data, and modeled, NMS has observed new twists to this basic surface boundary exosphere process.  NMS also observed helium and found a relationship with the He++ being delivered to the Moon by the solar wind.  LDEX has mapped out the height- and local time dependence of the tenuous lunar dust veil, finding that dust densities are highest on the ram side of the Moon, facing the direction of motion of the Earth-Moon system around the sun.  This much may be expected, but LDEX is revealing surprising new features.  Occasionally, LDEX observes a large, short-term (less than a few minutes) increase in dust density.  Evidently this is due to the impact of much larger meteoroids within a few minutes and tens to 100s of kilometers of LADEE. This talk will describe the mission and set the stage for talks by the science team members.