  Large-scale characterization of exoplanetary atmospheres is on the horizon,
thereby making it possible in the future to extract their statistical
properties. In this context, by using a well validated model in the solar
system, we carry out three-dimensional magnetohydrodynamic simulations to
compute nonthermal atmospheric ion escape rates of unmagnetized rocky
exoplanets as a function of their radius based on fixed stellar radiation and
wind conditions. We find that the atmospheric escape rate is, unexpectedly and
strikingly, a nonmonotonic function of the planetary radius $R$ and that it
evinces a maximum at $R \sim 0.7\,R_\oplus$. This novel nonmonotonic behavior
may arise from an intricate tradeoff between the cross-sectional area of a
planet (which increases with size, boosting escape rates) and its associated
escape velocity (which also increases with size, but diminishes escape rates).
Our results could guide forthcoming observations because worlds with certain
values of $R$ (such as $R \sim 0.7\,R_\oplus$) might exhibit comparatively
higher escape rates when all other factors are constant.
