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LADEE/LDEX Observations of Lunar Pickup Ion Distribution and Variability

Andrew Poppe
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Abstract Text: 

We present observations of lunar pickup ion distribution and variability taken serendipitously by the Lunar Dust Experiment (LDEX) onboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission. LDEX operated for an approximately six-month period between October 2013 and April 2014 and recorded dust impacts both directly and indirectly. The indirect dust detection mode, known as the “integrator”, was found on orbit to also be responsive to the flux of low energy lunar pickup ions originating from the lunar exosphere. We first describe the LDEX instrument and the “integrator” method of detecting lunar pickup ions, focusing on LDEX’s ability to make broad, high time resolution pickup ion flux measurements. By aggregating all the LDEX pickup current measurements and appropriately subtracting background current sources, we have identified several trends in the pickup ion flux including (i) an approximate scale height of 100 km, (ii) a linear, positive correlation with solar wind flux to the Moon, and (iii) a nearly flat distribution as a function of lunar local time, with some evidence of a peak near 07-08 h. We also compare the LDEX current measurements with a model for the exospheric ion production rate based off previous lunar neutral and ionized exospheric measurements. We find that LDEX data are consistent with ion production rates dominated by Al+, CO+, and Ar+, although the data do suggest that the Al+ production rate is less than previous model predictions.

Zach Ulibarri, Tobin Munsat, Richard Dee, Murthy S. Gudipati, Mihály Horányi, David James, Sascha Kempf, Zoltan Sternovsky
SSERVI Identifier: 

Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."