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Author Bu, Caixia ♦ Bahr, David A. ♦ Dukes, Catherine A. ♦ Baragiola, Raúl A.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ COSMIC DUST ♦ ERUPTION ♦ FILMS ♦ ICE ♦ INTERACTIONS ♦ PLASMA ♦ POROSITY ♦ SATELLITES ♦ SATURN PLANET ♦ SIMULATION ♦ SURFACE POTENTIAL ♦ SURFACES ♦ THERMAL CYCLING ♦ THICKNESS ♦ WATER ♦ WATER VAPOR
Abstract Within Saturn's E-ring, dust grains are coated by water vapor co-released with ice grains from the geyser-like eruptions of Enceladus. These ice-coated grains have intrinsic surface potential and interact synergistically with the ions and electrons of Saturn's magnetospheric plasmas. We perform laboratory experiments to investigate the effects of water-ice growth on the surface potential, using amorphous solid water (ASW) films. We estimate the growth of the surface potential to be ∼ 2.5 mV (Earth) yr{sup 1} and 112 mV yr{sup 1} for E-ring grains at ∼4.5 R {sub s} and 3.95 R {sub s} outside Enceladus’s plume, respectively. In addition, our measurements show that the linear relationship between the surface potential and the film thickness, as described in previous studies, has an upper limit, where the film spontaneously cracks above a porosity-dependent critical thickness. Heating of the cracked films with (and without) deposited charge shows that significant positive (and negative) surface potentials are retained at temperatures above 110 K, contrary to the minimal values (roughly zero) for thin, transparent ASW films. The significant surface potentials observed on micron-scale cracked ice films after thermal cycling, (5–20) V, are consistent with Cassini measurements, which indicate a negative charge of up to 5 V for E-ring dust particles at ∼5 R {sub s}. Therefore, the native grain surface potential resulting from water-vapor coating must be included in modeling studies of interactions between E-ring icy surfaces and Saturn's magnetospheric plasma.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2016-07-10
Publisher Place United States
Journal Astrophysical Journal
Volume Number 825
Issue Number 2


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