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Published October 2016 | Submitted + Published
Journal Article Open

A hypothesis for the color bimodality of Jupiter Trojans


One of the most enigmatic and hitherto unexplained properties of Jupiter Trojans is their bimodal color distribution. This bimodality is indicative of two sub-populations within the Trojans, which have distinct size distributions. In this paper, we present a simple, plausible hypothesis for the origin and evolution of the two Trojan color sub-populations. In the framework of dynamical instability models of early solar system evolution, which suggest a common primordial progenitor population for both Trojans and Kuiper Belt objects, we use observational constraints to assert that the color bimodalities evident in both minor body populations developed within the primordial population prior to the onset of instability. We show that, beginning with an initial composition of rock and ices, location-dependent volatile loss through sublimation in this primordial population could have led to sharp changes in the surface composition with heliocentric distance. We propose that the depletion or retention of H_2S ice on the surface of these objects was the key factor in creating an initial color bimodality. Objects that retained H_2S on their surfaces developed characteristically redder colors upon irradiation than those that did not. After the bodies from the primordial population were scattered and emplaced into their current positions, they preserved this primordial color bimodality to the present day. We explore predictions of the volatile loss model—in particular, the effect of collisions within the Trojan population on the size distributions of the two sub-populations—and propose further experimental and observational tests of our hypothesis.

Additional Information

© 2016 The American Astronomical Society. Received 2015 November 25; revised 2016 June 29; accepted 2016 July 12; published 2016 September 29. Discussions with the Keck Institute for Space Studies "In Situ Science and Instrumentation for Primitive Bodies" study group, including Bethany Ehlmann, Jordana Blacksberg, and John Eiler, were extremely valuable in the development of the model presented in this paper. We also thank Mario Melita for providing helpful comments and suggestions during the review process.

Attached Files

Published - Wong_2016_AJ_152_90.pdf

Submitted - 1607.04133v1.pdf


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August 22, 2023
October 23, 2023