Seasonally Varying Outgassing as an Explanation for Dark Comet Accelerations

TL;DR

This paper proposes that anisotropic outgassing due to differential heating and spin-pole obliquity can explain the unusual nonradial accelerations observed in certain dark comets, providing a plausible physical mechanism.

Contribution

The study introduces a balanced outgassing model with three parameters that successfully reproduces observed accelerations in dark comets, expanding understanding of nongravitational forces.

Findings

Model reproduces observed accelerations for most dark comets.

Derived formulae for component accelerations based on orbital parameters.

Outgassing mechanism plausibly explains nonradial accelerations in inactive objects.

Abstract

Significant nonradial, nongravitational accelerations with magnitudes incompatible with radiation-driven effects have been reported in seven small, photometrically inactive near-Earth objects. Two of these objects exhibit large transverse accelerations (i.e., within the orbital plane but orthogonal to the radial direction), and six exhibit significant out-of-plane accelerations. Here, we find that anisotropic outgassing resulting from differential heating on a nucleus with nonzero spin-pole obliquity, averaged over an eccentric orbit, can explain these accelerations for most of the objects. This balanced outgassing model depends on three parameters -- the spin pole orientation (R.A. and Dec.) and an acceleration magnitude. For these "dark comets" (excepting 2003 RM), we obtain parameter values that reproduce the observed nongravitational accelerations. We derive formulae for the component accelerations under certain assumptions for the acceleration scaling over heliocentric distance. Although we lack estimates of these objects' spin axes to confirm our values, this mechanism is nevertheless a plausible explanation for the observed accelerations, and produces accurate perturbations to the heliocentric motions of most of these objects. This model may also be applied to active objects outside of the dark comets group.