What a difference 200 km makes! NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) completed its third Orbit Lowering Maneuver (OLM) Nov. 10, and its fourth on Nov. 20. During the commissioning phase when ground controllers were checking out the instruments and spacecraft, LADEE was orbiting the moon 250 km above the surface. Now LADEE is in its science operations orbit. All three science instruments are taking data in their planned sequence. LADEE’s new orbit makes its closest approach to the moon’s surface (or periapsis altitude) between 20 and 50 km, and farthest point (or apoapsis altitude) between 75 and 150 km.
The instrument teams conducted some preliminary science activities while at the high commissioning altitudes. For example, the LADEE Neutral Mass Spectrometer (NMS) was able to observe atmospheric helium, which can reach high altitudes. The Lunar Dust EXperiment (LDEX), the first dedicated dust instrument to orbit the moon, began recording dust impacts as soon as the cover opened. A lunar dust exosphere was expected theoretically, and similar phenomena were seen by Galileo flybys of Jupiter’s icy moons. But LDEX has made the first measurements of such an exosphere at the moon. Both instruments make measurements by recording ambient conditions of gas and dust at LADEE’s position. LADEE also carries a remote sensing instrument, the Ultraviolet/Visible Spectrometer (UVS) that records light from atmospheric gases, which emit at specific wavelengths, and the scattered light from dust. UVS made measurements of atmospheric sodium and potassium at lunar sunset, sunrise and noon.
Everything changed when LADEE swooped down to 50 km above the moon’s surface after the third OLM Nov. 10. At that low vantage point, NMS was able to detect Argon-40 for the first time, and see its distinctive variation across the lunar dawn. Argon-40, a noble gas, has an atomic mass 10 times that of helium, and tends to stay closer to the lunar surface. The rate that LDEX was sensing lunar dust at high altitudes (approximately one dust grain per minute) suddenly increased several-fold at 50 km. And things got even better after the fourth OLM brought LADEE into its science orbit.
LDEX has been observing occasional bursts of dust particles, where rates increase from a steady few per minute to several hundreds of hits in under 30 seconds. These bursts may be due to LADEE flying through the dust plumes thrown up from the lunar surface when a meteoroid crashes into the lunar surface nearby.
NMS has continued to monitor helium and argon, and has now seen neon as well. New UVS measurements of potassium and sodium promise to tell us the origins of these exotic species. And the day after Thanksgiving, Nov. 29, three distinct meteoroid impacts on the moon were recorded by the Meteoroid Environment Office’s Lunar Impact Monitoring Program, based at NASA’s Marshall Space Flight Center. Knowing the location and time of these impacts, LADEE’s measurements of their effects can help us understand how atmospheric species can be produced by such events, and provide measurements of dust plumes they create.
Stay tuned as LADEE discovers how meteoroid impacts, and other exciting developments, may affect the moon’s tenuous atmosphere and dust environment!
Posted by: Soderman/SSERVI Staff
Source: NASA ARC/Rick Elphic