Energetic Particle Measurements on Mars and in Lunar Orbit

Cary J Zeitlin1, Don Hassler2, Nathan Schwadron3, Harlan E Spence4, Robert F Wimmer-Schweingruber5, Jan Kristoffer Appel6, Eckart Boehm6, Stefan S Boettcher6, David E Brinza7, Soenke Burmeister6, Bent Ehresmann8, Jingnan Guo9, Jan Kohler6, Henning Lohf6, Cesar Martin-Garcia10, Arik Posner11, Scot CR Rafkin2, Gerald weigle II12, Javier Martín-Torres13 and María-Paz Zorzano13, (1)Leidos Innovations Corporation, SRAG, Houston, TX, United States, (2)Southwest Research Institute Boulder, Boulder, CO, United States, (3)Los Alamos National Laboratory, Los Alamos, United States, (4)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, (5)University of Kiel, Institute for Experimental and Applied Physics, Kiel, Germany, (6)University of Kiel, Kiel, Germany, (7)Jet Propulsion Laboratory, Pasadena, CA, United States, (8)Southwest Research Institute Boulder, Solar System Science & Exploration Division, Boulder, CO, United States, (9)University of Science and Technology of China, School of Earth and Space Sciences, Hefei, China, (10)IEAP, University of Kiel, Kiel, Germany, (11)NASA Headquarters, SMD/Heliophysics Division, Washington, DC, United States, (12)Big Head Endian, Burden, KS, United States, (13)Centro de Astrobiologia, Madrid, Spain
Abstract:
The Radiation Assessment Detector (RAD) aboard the Curiosity rover has been making measurements of energetic particles on the surface of Mars since the rover landed in August 2012. RAD also acquired data for most of the cruise to Mars, from Dec. 2011 through July 2012. In both cruise and on the surface, RAD is under considerable shielding, averaging 22 g cm-2 of CO2 during the surface mission, and ~ 16 g cm-2 during cruise. The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) aboard the LRO spacecraft in lunar orbit has been making measurements since mid-2009. CRaTER contains three sets of detectors, of which one is unshielded, one is under 6 g cm-2 of tissue-equivalent plastic (TEP) shielding, and one is under 9 g cm-2 of TEP. Taken together, the two experiments provide a wealth of data concerning the effects of shielding on Galactic Cosmic Rays (GCRs) and Solar Energetic Particles (SEPs). Comparison of data from the two instruments is complicated by their different locations in the heliosphere, which at most times causes them to be magnetically connected to different regions on the Sun. Variability of the atmospheric shielding above RAD, which is both diurnal and seasonal, also influences the comparison. During solar quiet time, when the energetic particle flux is due to GCRs, many similarities – and some small but significant differences – are seen in detailed time series data. In contrast, during SEP events, both the shielding and location disparities cause large differences in the measured particle fluxes.
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