Seasonally Varying Outgassing as an Explanation for Dark Comet Accelerations

Significant nonradial nongravitational accelerations whose magnitudes are incompatible with 13 radiation-driven effects have been reported in seven photometrically inactive near-Earth objects. Two 14 of these objects exhibit large transverse accelerations, and six exhibit significant out-of-plane accel15 erations. Here we find that anisotropic outgassing resulting from differential heating on a nucleus 16 with nonzero obliquity, averaged over an eccentric orbit, can explain these nonradial nongravitational 17 accelerations for most of these objects. Our model depends on three parameters — the spin pole direc18 tion and an acceleration magnitude. For these “dark comets” (excepting 2006 RH120 and 2003 RM), 19 we obtain parameter values which reproduce the observed nongravitational accelerations. We derive 20 formulae for the component accelerations under certain assumptions for the acceleration scaling over 21 heliocentric distance. While we lack estimates of these objects’ spin axes to confirm our values, this 22 mechanism explains the accelerations and produces accurate perturbations to the heliocentric motions 23 of most of these objects, and may be responsible for their nongravitational accelerations.