JFC Reflectivity Reassessed: Preliminary Albedos and Statistical Trends

Comets are widely viewed as preserving some of the compositional and structural properties of the planetesimals in the solar system during its formation. Studying their current physical properties is essential for understanding their surface evolution over time. Albedo is an intrinsic physical property influenced by an object’s material composition, porosity, regolith, and surface roughness, and is important for context when studying e.g. shape, color, and surface heterogeneity. Cometary nuclei generally do have very low albedo values, alluding to their primitive surfaces. However, the actual geometric albedo distribution of comets is not well-constrained, as literature provides this quantity for only 29 comets, with 19 of those being Jupiter Family Comets (JFCs) [1]. The lack of albedo values is due to multiple observational limitations. First, comae tend to obscure the comet nuclei when they are best observable, and second, each target’s radius must be obtained independently. We present here preliminary results from our work to measure the JFC albedo distribution in a statistically significant subset of the population by avoiding both of these problems. We have obtained R-band imaging photometry of about 100 JFC nuclei with known, independent radii from the SEPPCoN survey using the Spitzer telescope [2] and other sources [1]. We have generally made use of 3-8 meter telescopes (e.g. ARC at Apache Point, VLT, PAL200) to observe these comets at multiple epochs when they are ~3-5 au from the Sun, i.e. when the nuclei, while faint, have minimal or no activity. A montage of our Apache Point data can be seen in the figure below. To avoid too much extrapolation, we reference our results to a 10 degree phase angle, and assume a typical linear phase coefficient of 0.04 mag/deg. We will present our albedo analysis thus far, including an assessment of the mean albedo and of any possible anomalous albedos, and a comparison of JFC albedos with those of related populations such as Centaurs, Trojans, and Trans-Neptunian Objects (TNOs). The results of this work have the potential to provide much needed insight into the current distribution of albedo values for JFCs, and will help constrain their placement in the broader population of small bodies albedos. We hope to in the future make use of publicly available infrared (e.g. SPHEREx, NEO-Surveyor) and visible (e.g. Vera Rubin Observatory) data to augment the sample size of albedos. Acknowledgements: We acknowledge support from NASA’s SSERVI program via award 80NSSC19M0214 for the Center for Lunar and Asteroid Surface Science. [1] M. M. Knight, et al. Physical and Surface Properties of Comet Nuclei from Remote Observations, in Comets III (K. J. Meech et al., Eds.), U. Arizona Press, Tucson, 2024, pp. 361-404.  [2] Y. R. Fernández, et al. Icarus, 226, 1138, 2013.