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Relationship between the phase-function slope and albedo of comets, asteroids and asteroids on cometary orbits

Presentation #514.02 in the session “Hints of Cometary Activity”.

Published onOct 26, 2020
Relationship between the phase-function slope and albedo of comets, asteroids and asteroids on cometary orbits

In this work, we compare the relationship between the linear phase-function slope (β) and the geometric albedo of Jupiter-family comets (JFCs) to other minor planet populations: Trans-Neptunian Objects, Centaurs, Jupiter Trojans, Hildas, Main-belt asteroids (MBAs) and Near-Earth objects (NEOs). With this analysis, we test whether these two parameters are a good indicator of the surface differences among the populations and probe whether they can be used to study the surface evolution of small bodies.

We have previously identified a correlation of increasing albedo for increasing phase-function slope from a sample of 14 JFCs [1]. This was interpreted as an evolutionary path of comets, according to which, dynamically young JFCs start their evolution with relatively large albedos and steeper phase functions. Then, during their lifetimes, sublimation-driven erosion gradually makes the comets’ surfaces smoother, and their phase-function slopes and albedos decrease. Interestingly, the correlation identified for JFCs follows the opposite trend to that identified for MBAs and NEOs (Fig. 1)[2,3].

In this work, we aim to expand the study of the phase-function—albedo relationship to a greater number of objects. We collected objects from all populations with known β and geometric albedo. We also constructed a large dataset of MBAs, NEOs, ACOs, Jupiter Trojans, and Hildas with albedos from WISE/NEOWISE, Spitzer and AKARI. To complement them, we used photometric observations from the Minor Planet Center to derive their phase functions. Even though the individual β and albedos can have relatively large uncertainties, the large number of objects allowed us to characterize well the relationship between β and geometric albedo of the different populations.

This presentation will give a special emphasis on our ongoing work to compare ACOs with JFCs and asteroids. We have found that low-albedo ACOs in the NEAs population, as well as most ACOs from the MBAs group, have β similar to those of the lowest-albedo comets. Only a few of the Main-belt ACOs overlap with the phase-angle–albedo region where the high-albedo (and possibly least processed) JFCs are found. The lack of NEOs in this domain suggests that the decrease of perihelion distance is connected to a decrease in β. Even though these trends are based on a relatively small sample of objects with only sparsely sampled phase functions, they have potentially very interesting implications and should be investigated with further observations.

  1. Kokotanekova+, 2018, MNRAS 479, 4665

  2. Belskaya & Shevchenko, 2000, Icarus, 147, 94

  3. Hergenrother+, 2013, Icarus, 226, 1, 663


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