Implications of the small spin changes measured for large Jupiter-family comet nuclei

R Kokotanekova,P Lacerda,P Nikolov,S F Green,T Bonev,C Snodgrass

doi:10.1093/mnras/sty1529

Abstract

Rotational spin-up due to outgassing of comet nuclei has been identified as a possible mechanism for considerable mass-loss and splitting. We report a search for spin changes for three large Jupiter-family comets (JFCs): 14P/Wolf, 143P/Kowal-Mrkos, and 162P/Siding Spring. None of the three comets has detectable period changes, and we set conservative upper limits of 4.2 (14P), 6.6 (143P) and 25 (162P) minutes per orbit. Comparing these results with all eight other JFCs with measured rotational changes, we deduce that none of the observed large JFCs experiences significant spin changes. This suggests that large comet nuclei are less likely to undergo rotationally-driven splitting, and therefore more likely to survive more perihelion passages than smaller nuclei. We find supporting evidence for this hypothesis in the cumulative size distributions of JFCs and dormant comets, as well as in recent numerical studies of cometary orbital dynamics. We added 143P to the sample of 13 other JFCs with known albedos and phase-function slopes. This sample shows a possible correlation of increasing phase-function slopes for larger geometric albedos. Partly based on findings from recent space missions to JFCs, we hypothesise that this correlation corresponds to an evolutionary trend for JFCs. We propose that newly activated JFCs have larger albedos and steeper phase functions, which gradually decrease due to sublimation-driven erosion. If confirmed, this could be used to analyse surface erosion from ground and to distinguish between dormant comets and asteroids.

Highlights

It is widely accepted that comets are among the most unaltered bodies in the Solar System
Considering all of the evidence presented above, we propose the following hypothesis to explain the correlation between β and geometric albedo: Dynamically young Jupiter-family comets (JFCs) begin their lives as active comets having volatile-rich and rough surfaces characterised by tall steep cliffs
With the new observations we have increased the number of JFCs with studied period changes from eight to eleven

Summary

Introduction

It is widely accepted that comets are among the most unaltered bodies in the Solar System. They are known to undergo dramatic changes driven by sublimation activity. Understanding the effects of cometary evolution is key for discerning their primordial properties and relating them to the early Solar-system history. Having orbital periods of less than twenty years, Jupiter-family comets (JFCs) allow repeated observations over multiple apparitions (and perihelion passages). These observations can be used to monitor the changes in activity, rotation and surface properties experienced by the comets. The relatively low eccentricity and inclination of JFCs as well as their relative proximity to Earth has made them accessible to several space missions which have improved the understanding of cometary physics tremendously over the past few decades

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