Bulk Properties and Evolution of Jupiter-Family Comet Nuclei

Kokotanekova, Rosita (2018). Bulk Properties and Evolution of Jupiter-Family Comet Nuclei. PhD thesis The Open University.

Abstract

This thesis presents the results from photometric time-series observations of Jupiter-family comets (JFCs). A method was developed that allows mutual absolute photometric calibration of data taken at different epochs with different instruments and results in absolute-calibration uncertainty of ∼0.02 mag. The method was applied to various datasets with the goal of studying the rotation rates and surface properties of ten comets.

Previously published properties of JFCs were collected and complemented by new results. The resulting comprehensive sample was used to study the ensemble properties of JFC nuclei. It confirmed the cut-off in bulk density at ∼0.6 g cm−3 and provided evidence for a lower limit on the bulk tensile strength of 10-25 Pa.

New lightcurves of three JFCs were used to look for spin changes over their last orbits. None of the observed comets had detectable period changes, and strict conservative upper limits were set. Comparing these results with all eight other JFCs with measured rotational changes suggests that large JFCs are less likely to undergo rotationally-driven mass-loss, and are therefore more likely to survive more perihelion passages than smaller nuclei. This conclusion is supported by evidence from the cumulative size distributions of JFCs and dormant comets, as well as from recent dynamical simulations.

This work almost doubled the sample of JFCs with both albedos and phase-function slopes known. The extended sample shows a possible correlation of increasing phase-function slopes for larger geometric albedos, which can be interpreted as an evolutionary trend for JFCs. According to this hypothesis, newly activated JFCs have higher albedos and steeper phase functions, which gradually decrease due to sublimation-driven erosion. If confirmed, this correlation could be used to analyse surface erosion from the ground and to distinguish between dormant comets and asteroids.

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