Comet 81/P Wild 2: changes in the spin axis orientation during the last five apparitions

TL;DR

This study tracks changes in the spin axis orientation of comet 81P Wild 2 over five apparitions, revealing a slow drift likely caused by outgassing forces affecting its rotation and orbit.

Contribution

It provides new measurements of the comet's spin axis during recent apparitions and demonstrates a long-term drift in its orientation over multiple decades.

Findings

The spin axis of 81P Wild 2 has a measurable drift over five apparitions.

Outgassing-induced jet forces likely cause the observed spin axis drift.

The comet's non-gravitational perturbations influence its orbital and rotational dynamics.

Abstract

Comet 81P (Wild 2) is characterized by the presence of a prominent-fan shaped dust emission originating from an active source at high latitude on the nucleus, whose axis is assumed to coincide with the comet's rotation axis. Therefore, several authors estimated the spin axis orientation of 81P in past apparitions based on the polar jet model. By measuring the PAs of the fan on CCD images taken with different telescopes during the 2009-10 and 2022-23 apparitions, we estimated a position of the comet's spin axis at RA=295.0{\deg}$\pm$ 7.5{\deg}, Dec=14.5{\deg}$\pm$ 4.0{\deg} for the 2009-10 apparition and at RA=296.7{\deg}$\pm$ 2.0{\deg}, Dec=17.3{\deg}$\pm$ 2.5{\deg} for the 2022-23 apparition. Despite some degree of uncertainty of the estimate for the 2009-10 apparition, we interpolated the estimate for 2009-10 and 2022-23 with the published data of the previous apparition of 1997, to assess the presence and the extent of a drift of the pole since the 1997 passage. The analysis over a long time span of five consecutive apparitions confirms previous observations that the spin axis of comet 81P is subject to a slow drift with variable rate, probably connected to outgassing-induced jet forces and the related non-gravitational perturbations of its orbital period.