  By using a hydrodynamic atmospheric escape mechanism \citep{amit09} 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
\citep{delsanti10,cook07}. 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 AZ$_{84}$ 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.
