Probing the origin of the dark material on Iapetus

Abstract

Among the icy satellites of Saturn, Iapetus shows a striking dichotomy between its leading and trailing hemispheres, the former being significantly darker than the latter. Thanks to the VIMS imaging spectrometer on-board Cassini, it is now possible to investigate the spectral features of the satellites in Saturn system within a wider spectral range and with an enhanced accuracy than with previously available data. In this work, we present an application of the G-mode method to the high resolution, visible and near infrared data of Phoebe, Iapetus and Hyperion collected by Cassini/VIMS, to search for compositional correlations. We also present the results of a dynamical study on the efficiency of Iapetus in capturing dust grains travelling inward in Saturn system to evaluate the viability of Poynting-Robertson drag as the physical mechanism transferring the dark material to the satellite. The results of spectroscopic classification are used jointly with the ones of the dynamical study to describe a plausible physical scenario for the origin of Iapetus' dichotomy. Our work shows that mass transfer from the outer Saturnian system is an efficient mechanism, particularly for the range of sizes hypothesised for the particles composing the newly discovered outer ring around Saturn. Both spectral and dynamical data indicate Phoebe as the main source of the dark material. However, we suggest a multi-source scenario where now extinct prograde satellites and the disruptive impacts that generated the putative collisional families played a significant role in supplying the original amount of dark material.

20 pages, 4 tables, 11 figures, major revision (manuscript extended and completed, figures added and corrected, new results added), minor revision and finalization of author list, moderate revision (update of the manuscript following reviewer's feedback and discovery of the new Saturnian outer ring)

References in corpus (4)

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Cited by in corpus (11)

• Saturn's icy satellites and rings investigated by Cassini - VIMS. III. Radial compositional variability
• The Comparative Exploration of the Ice Giant Planets with Twin Spacecraft: Unveiling the History of our Solar System
• Finding the trigger to Iapetus' odd global albedo pattern: Dynamics of dust from Saturn's irregular satellites
• The radial distribution of water ice and chromophores across Saturn's system
• Saturn's icy satellites investigated by Cassini - VIMS. IV. Daytime temperature maps
• NEOWISE: Observations of the Irregular Satellites of Jupiter and Saturn
• Chaotic dust dynamics and implications for the hemispherical color asymmetries of the Uranian satellites
• Cladistical analysis of the Jovian and Saturnian satellite systems
• First observations of the Phoebe ring in optical light
• Radial profiles of the Phoebe ring, a vast debris disk around Saturn
• Silicates on Iapetus from Cassini's Composite Infrared Spectrometer