The sublimative torques of Jupiter Family Comets and mass wasting events on their nuclei

Abstract

Sublimative outgassing of comets produces torques that alter the rotation state of their nuclei. Recently, parameterized sublimative torque models have been developed to study rotation state changes of individual comet nuclei and populations of cometary bodies. However, these models simplify the interactions between the escaping gas and cometary surface into only a few parameters that hide the details of these complex interactions. Here we directly compare the Xparameter model (Samarasinha & Mueller, 2013) with the SYORP model (Steckloff & Jacobson, 2016) to tease out insights into the details of the gassurface interactions driving sublimative torques. We find that, for both of these models to accurately model sublimative torques, the number of sublimating molecules that contribute to the net torque is largely independent of the detailed shape and activity of the nucleus, but rather depends primarily on the size of the nucleus and the effective heliocentric distance of the comet. We suggest that cometary activity must be largely restricted to regions of steep gravitational surface slopes (above the angle of repose), where mass wasting can refresh activity by shedding mantles of refractory materials and exposing fresh volatiles. We propose a new classification scheme for comets based on the frequency of this mass-wasting process (relative to the timescale of activity fading): quasiequilibrium, episodic, quasi-dormant, and extinct.

29P/Schwassmann–Wachmann 1, A Centaur in the Gateway to the Jupiter-family Comets

“…Prialnik et al 2004), sublimative torques that can spin up nuclei and trigger mass wasting or splitting (e.g. Steckloff & Jacobson 2016;Steckloff & Samarasinha 2018), and localized erosion that can induce mass loss (e.g. Vincent et al 2017).…”

Ancient and present surface evolution processes in the Ash region of comet 67P/Churyumov-Gerasimenko

“…Cliff collapse is an important process that reshapes the nucleus surface of a comet (Britt et al 2004;Pajola et al 2015Pajola et al , 2016Pajola et al , 2017Steckloff et al 2016;Steckloff & Samarasinha 2018;Lucchetti et al 2019). The morphology of the associated deposits is controlled by different factors such as the topography, the slope, the mechanical properties of the collapsing material, the presence of volatiles, and the insolation conditions (Cruden 1996;Martha et al 2010;Hungr et al 2013).…”

“…From December 2014 to June 2016, tens of morphological changes have been observed. Changes arise as a modification or a creation of new landscapes on the surface; in particular, cliff collapse appears to be a key process that reshapes the surface (Britt et al 2004;Pajola et al 2015Pajola et al , 2016Pajola et al , 2017Steckloff et al 2016;Steckloff & Samarasinha 2018;Lucchetti et al 2019). In the Imhotep region Groussin et al (2015b) observed morphological changes in the form of roundish features growing in a preferential direction.…”

The Rocky‐Like Behavior of Cometary Landslides on 67P/Churyumov‐Gerasimenko

“…On 67P, multiple landslide deposits are identified in close association with cliffs. These observations suggest that cliff collapse is an important process in reshaping cometary surfaces (Britt et al, ; Pajola et al, ; Steckloff et al, ; Steckloff & Samarasinha, ). OSIRIS observations show a direct evidence of the occurrence of a cometary landslide, with the resulting production of a newly formed boulder talus located at the base of the scarp (see the Aswan case; Pajola et al, ).…”