Interfacial Tension-Driven Differentiation-(ITDD) may result in a low-density central region inside kilometer-sized bodies

Interfacial Tension-Driven Differentiation, (ITDD), and its possible significance with regards to the interior structures of kilometer-sized bodies is discussed. Using a simple physical and geometrical model, an analytical expression for the conditions in which ITDD can occur is derived. It is shown that ITDD coupled with internal convection can lead to a counterintuitive result: that central regions may be less dense than outer regions in km-sized, initially melted bodies. ITDD offers an alternative explanation to the formation of microporosity inside of small bodies, (e.g. Churyumov-Gerasimenko-like objects), as well as macroporosity, which is suggested to occur in the interior of Mars' larger satellite Phobos, without recourse to rubble-pile models. Depending on the development of the velocity boundary layer at the solidification front, ITDD allows not just the possibility of central porosity, but also more complex scenarios, such as the formation of internal porosity rings.