A Hypothesis for the Color Diversity of the Kuiper Belt
We propose a chemical and dynamical process to explain the surface colors of the Kuiper belt. In our hypothesis, the initial bulk compositions of the bodies themselves can be quite diverse—as is seen in comets—but the early surface compositions are set by volatile evaporation after the objects are formed. Strong gradients in surface composition, coupled with UV and particle irradiation, lead to the surface colors that are seen today. The objects formed in the inner part of the primordial belt retain only H_2O and CO_2 as the major ice species on their surfaces. Irradiation of these species plausibly results in the dark neutrally colored centaurs and Kuiper belt objects (KBOs). Object formed further in the disk retain CH_3OH, which has been shown to lead to brighter redder surfaces after irradiation, as seen in the brighter redder centaurs and KBOs. Objects formed at the current location of the cold classical Kuiper belt uniquely retain NH_3, which has been shown to affect irradiation chemistry and could plausibly lead to the unique colors of these objects. We propose observational and experimental tests of this hypothesis.
Additional Information© 2011 The American Astronomical Society. Received 2011 May 24; accepted 2011 August 19; published 2011 September 12. This research has been supported by grant NNX09AB49G from the NASA Planetary Astronomy program. We thank Hal Levison, Rosario Brunetto, and Konstantin Batygin for enlightening conversations.
Published - Brown2011p16003Astrophys_J_Lett.pdf
Submitted - 1109.0298.pdf