 Dust-destruction feedback at a sublimation front

A thermal-stability argument that holds dust properties fixed can fail near a sublimation front. A rise in temperature can destroy grains, changing the absorption and emission efficiencies, the dust mass and the optical depth through which radiation reaches neighboring material. The heating and cooling laws then change along with the temperature.

Write the net heating schematically as $Q(T,a,{\rho }_d)$, where $a$ is grain size and ${\rho }_d$ is dust density. The response along an evolving state includes $Q_{a}da/dT$ and $Q_{{\rho }_d}d{\rho }_d/dT$, not only the fixed-grain derivative $Q_T$. These additional terms can reinforce or oppose the perturbation. The sign depends on geometry, radiation spectrum and dust–gas coupling, so the fixed-property result in thermal stability of externally heated blackbody dust does not by itself establish the stability of a sublimation front.