The Kuiper belt is a mass of bodies that extends in a heliocentric ring, approximately from 30 to 55 AU. Some scattered bodies are known to reach heliocentric distances of about 100 AU and beyond.

About 100,000 bodies, with diameters larger than 100km, are believed to occupy this belt.  Among those are objects whose diameters are in the order of 1000km.

As KBOs are considered remnants from the epoch of planet formation, they are assumed to be pristine bodies that have undergone little alteration. Our study looks at possible alterations in KBO surface ice composition due to a hydrodynamic atmospheric escape mechanism.

We show that for the low body surface temperatures prevailing in the Kuiper belt and for bodies whose diameter is several hundreds of kilometers, the ratio of thermal to gravitational pressure is of the same order of magnitude as that at the base of the solar corona.

By adapting the solar corona theory to the case of small and cold objects we have obtained an analytical description of a possible hydrodynamic gas flow off of some intermediate sized KBOs.   

This model allows us to provide a simple explanation for the methane dichotomy seen in KBOs, where large objects (e.g. Quaoar, Makemake etc.) show traces of methane ice on their surface while small KBOs (e.g. Orcus, Charon etc. ) seem to be depleted in this volatile ice.

We show that our model for selective volatile surface ice retention is capable of constraining the mass density of intermediate sized KBOs without the need for measuring the motion of a binary companion. The constrained mass density, for some cases, is stringent enough to tell whether the object is mostly water ice or rock. 

We also study the effect of a global gravitating dust atmosphere on a possible hydrodynamic gas flow off the surface of a KBO and estimate such a dust atmosphere optical depth. Such optical depth estimates should hopefully aid astronomers in constraining the unknowns in the theory as KBO observational techniques and tools improve.