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Stairstep Particle Flux Spectra on the Lunar Surface: Evidence for Nonmonotonic Potentials?

Author: 
Michael Collier
Topic: 
Exosphere
Delivered As: 
Oral
Abstract Text: 

We present examples of unusual “stairstep” differential flux spectra observed by the Apollo 14 Superthermal Ion Detector Experiment (SIDE) on the lunar dayside surface in Earth’s magnetotail. These spectra exhibit a relatively constant differential flux below some cut-off energy and then drop off precipitously, by about an order of magnitude or more, at higher energies. We propose that these spectra result from photoions accelerated on the lunar dayside by nonmonotonic potentials, potentials that do not decay to zero monotonically, and present a model for the expected differential flux. The energy of the cut-off and the magnitude of the differential flux are related to the properties of the local space environment and are consistent with the observed flux spectra. If this interpretation is correct, these surface-based ion observations provide a unique perspective that both complements and enhances the conclusions obtained by remote-sensed orbiter observations on the Moon’s exospheric and electrostatic properties.

Co-Authors: 
Michael Deluca, Mihaly Horanyi, Diego Janches, Tobin Munsat, Zoltan Sternovsky
SSERVI Identifier: 
NESF2016-031

About SSERVI
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."