High energy electron sintering of icy regoliths: Formation of the PacMan thermal anomalies on the icy Saturnian moons

The near-surface electron radiation environment of Saturn's moon Mimas

“…In the context of the CIRS and VIMS 87 observations of surface temperatures, it has been suggested that the energetic 88 electrons may sinter ice grains together, thus increasing the grain contact boundaries 89 and the thermal conductivity (Howett et al, 2011;Schaible et al, 2016). With regards 90 to the ISS color anomaly, it has been proposed that the electrons produce defects and 91 small voids in surface ice, leading to enhanced scattering at the wavelengths relevant 92 to the ISS UV3 filter (Schenk et al, 2011).…”

Radiation Effects on Airless Bodies in Space: Radiolysis, Sputtering, and Sintering in Regoliths

“…], although studying returned materials, meteorites, and analog samples in the laboratory [Pieters et al, 1993;Schaible and Baragiola, 2014] greatly aids interpretation. Additionally, computational methods can be used to simulate the weathering processes to explain various observed features [Hurley et al, 2012;Schaible et al, 2016], or more basic modeling can be carried out to predict what chemical and physical environments might be expected in early solar systems similar to our own [Hincelin et al, 2015;Drozdovskaya et al, 2016]. Simulations can be based on continuum descriptions of the micro-physical processes or directly simulate molecular level interactions [Arasa et al, 2010].…”

“…This work was originally motivated by an invitation to participate in a NASA Discovery Mission proposal for the Phobos And Deimos Mars Explorer (PADME), submitted in Feb 2015, and part of the work was used in the senior thesis of undergraduate astronomy student Adam Hutcherson. The primary work of this thesis is contained in Case 3, which provides a combined theoretical and computational description for electron induced sintering of water ice grains and shows that anti-corotational electrons in Saturn's magnetosphere are responsible for the so called PacMan thermal anomalies identified on the icy mid-sized moons Mimas, Tethys and Dione [Schaible et al, 2016]. Below we introduce each of the case studies presented in this thesis and discuss them in the context of their identification and accepted origin or, as in Case 2, their potential for new discovery.…”

“…As shown in Subsection 5.3.6, the model chosen was validated using continuum simulations performed by S. Piqueux (JPL) for water ice grains in a simple cubic packing configuration. This work has been published in Icarus [Schaible et al, 2016].…”

“…As described in Schaible et al [2016], the measured electron properties in the inner Saturnian system are used together with simulations carried out using the Monte Carlo program PENELOPE and a theoretical approach to computing spherical grain sintering rates on the icy Saturnian satellites to estimate the grain sintering timescales required to produce the observed thermal differences described in Chapter 5. Section 6.1.2 introduces the basics of grain sintering and gives a basic approach to calculating the volume rate of change for grains in contact.…”