A Rotational Disruption Crisis for Zodiacal Dust

A systematic torque from anisotropic radiation can rapidly spin up irregular grains to the point of breakup. We apply the standard theory of rotational disruption from radiative torques to solar system grains, finding that grains with radii ∼0.03–3 μm at 1 au from the Sun are spun to the point of breakup on timescales ≲1 yr even when assuming them to have an unrealistically high tensile strength of pure meteoritic iron. Such a rapid disruption timescale is incompatible with both the abundance of micron-sized grains detected in the inner solar system and with the low production rate of β-meteoroids. We suggest the possibility that zodiacal grains have a strong propensity to attain rotational equilibrium at low angular velocity (a so-called low-J attractor) and that the efficacy of rotational disruption in the solar system—and likely elsewhere—has been greatly overestimated.