Estimating the density of intermediate size KBOs from considerations of volatile retention

By using a hydrodynamic atmospheric escape mechanism (Levi, A., Podolak, M. [2009]. Icarus 202, 681–693) we show how the unusually high mass density of Quaoar could have been predicted (constrained), without any knowledge of a binary companion. We suggest an explanation of the recent spectroscopic observations of Orcus and Charon [Delsanti, A., Merlin, F., Guilbert, A., Bauer, J., Yang, B., Meech, K.J., 2010. Astron. Astrophys. 520, A40; Cook, J.C., Desch, S.J., Roush, T.L., Trujillo, C.A., Geballe, T.R., 2007. Astrophys. J. 663, 1406–1419]. We present a simple relation between the detection of certain volatile ices and the body mass density and diameter. As a test case we implement the relations on the KBO 2003 AZ84 and give constraints on its mass density. We also present a method of relating the latitude-dependence of hydrodynamic gas escape to the internal structure of a rapidly rotating body and apply it to Haumea.