The opposition effect in the outer Solar System: a comparative study of the phase function morphology


1 In this paper, we characterize the morphology of the disk-integrated phase 2 functions of satellites and rings around the giant planets of our Solar Sys3 tem. We find that the shape of the phase function is accurately represented 4 by a logarithmic model (Bobrov, 1970, in Surfaces and Interiors of Planets 5 and Satellites, Academic, edited by A. Dollfus). For practical purposes, we also 6 parametrize the phase curves by a linear-exponential model (Kaasalainen et al., 7 2001, Journal of Quantitative Spectroscopy and Radiative Transfer, 70, 529– 8 543) and a simple linear-by-parts model (Lumme and Irvine, 1976, Astronom9 ical Journal, 81, 865–893), which provides three morphological parameters : 10 the amplitude A and the Half-Width at Half-Maximum (HWHM) of the oppo11 sition surge, and the slope S of the linear part of the phase function at larger 12 phase angles. 13 Our analysis demonstrates that all of these morphological parameters are cor14 related with the single scattering albedos of the surfaces. 15 By taking more accurately into consideration the finite angular size of the Sun, 16 we find that the Galilean, Saturnian, Uranian and Neptunian satellites have 17 similar HWHMs (.0.5), whereas they have a wide range of amplitudes A. 18 The Moon has the largest HWHM (∼2). We interpret that as a consequence 19 of the “solar size bias”, via the finite size of the Sun which varies dramatically 20 from the Earth to Neptune. By applying a new method that attempts to mor21 phologically deconvolve the phase function to the solar angular size, we find 22 that icy and young surfaces, with active resurfacing, have the smallest values 23 of A and HWHM, whereas dark objects (and perhaps older surfaces) such as 24 the Moon, Nereid and Saturn’s C ring have the largest A and HWHM. 25 Comparison between multiple objects also shows that Solar System objects 26

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@inproceedings{Dau2009TheOE, title={The opposition effect in the outer Solar System: a comparative study of the phase function morphology}, author={Estelle D{\'e}au and Luke Dones and S{\'e}bastien Rodriguez and Sebastien Charnoz and Andre Brahic}, year={2009} }