= Radiation pressure on circumplanetary dust
The leading uniform stellar <radiation pressure> is a differential <acceleration> relative to a <planet>, of scale $\beta GM_\star/a_p^2$. Relative to planetocentric gravity at dust radius $a$, its magnitude is
$$
\eta_{\rm rad}=\beta\frac{M_\star}{M_p}\left(\frac a{a_p}\right)^2.
$$
Thus lying inside a <Hill sphere> alone does not guarantee small radiative perturbations. Approximately circular tightly bound dust requires this ratio sufficiently small, as well as weak tides; the uniform radiative <force> can otherwise excite <orbital eccentricity> or unbind grains.
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