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Chaotic rotation and evolution of asteroids and small planets in high-eccentricity orbits around white dwarfs

Observed planetary debris in white dwarf atmospheres predominately originate from the destruction of small bodies on highly eccentric ($>0.99$) orbits. Despite their importance, these minor planets have coupled physical and orbital evolution which has remained largely unexplored. Here, we present a novel approach for estimating the influence of fast chaotic rotation on the orbital evolution of high-eccentricity triaxial asteroids, and formally characterize the propagation of their angular rotation velocities and orbital elements as random time processes. By employing the impulse approximation, we demonstrate that the violent gravitational interactions during periastron passages transfer energy between the orbit and asteroid's rotation. If the distribution of spin impulses were symmetric around zero, then the net result would be a secular decrease of the semimajor axis and a further increase of the eccentricity. We find evidence, however, that the chaotic rotation may be self-regulated in such a manner that these effects are reduced or nullified. We discover that asteroids on highly eccentric orbits can break themselves apart --- in a type of YORP-less rotational fission --- without actually entering the Roche radius, with potentially significant consequences for the distribution of debris and energy requirements for gravitational scattering in metal-polluted white dwarf planetary systems. This mechanism provides a steady stream of material impacting a white dwarf without rapidly depleting the number of small bodies in the stellar system.