  Predicting transport rates of windblown sand is a central problem in aeolian
research, with implications for climate, environmental, and planetary sciences.
Though studied since the 1930s, the underlying many-body dynamics is still
incompletely understood, as underscored by the recent empirical discovery of an
unexpected third-root scaling in the particle-fluid density ratio. Here, by
means of grain-scale simulations and analytical modeling, we elucidate how a
complex coupling between grain-bed collisions and granular creep within the
sand bed yields a dilatancy-enhanced bed erodibility. Our minimal saltation
model robustly predicts both the observed scaling and a new undersaturated
steady transport state that we confirm by simulations for rarefied atmospheres.
