A Census Before Rubin of Asteroid Families in the Main Belt

Abstract

A collisional family is a collection of >km-size asteroid fragments produced by a large scale collision between asteroids. Here we cataloged 335 notable collisional families in the main asteroid belt. When possible, we estimated each family's formation age, mean visible albedo, taxonomic type, and parent body size. We found that older families (t_age>10 Myr) produced by impacts on small parent bodies (diameter D<5 km) are rarely identified because small members of these families have drifted over time by the Yarkovsky effect and blended with the background. The young families (t_age<10 Myr) typically have small parent bodies (D<10 km) as large asteroids do not disrupt often enough. The full catalog, including membership files for 335 individual asteroid families, is available for download (https://www.boulder.swri.edu/~davidn/Proper25).

Figures (3)

• Figure 1: The 335 collisional families reported in this catalog. The main belt is divided into the inner belt ($a_{\rm P}<2.5$ au; red), middle belt ($2.5<a_{\rm P}<2.82$ au; green) and outer belt ($a_{\rm P}>2.82$ au; blue). The upper part of the belt with $i_{\rm P}>17.5$ deg is highlighted by lighter colors. The black dots show members of the identified families. The labels indicate the proposed FIN designations of families in different main belt regions.
• Figure 2: The best-fit V envelope for the Merxia family ($C_0=3 \times 10^{-5}$ AU, red lines; the black dots are the HCM family members). Asteroid 808 Merxia is perfectly centered in the V shape envelope and is likely the true largest member in the family. Asteroids 1327, 6633 and 50694 are suspected interlopers. The Merxia family age is estimated to be $\sim 500$ Myr from Eq. (\ref{['tage']}), but the previous detailed Yarkovsky-YORP chronology modeling established $t_{\rm age}=250 \pm 100$ Myr (Vokrouhlický et al. 2006). This illustrates a case where the V envelope method can significantly overestimate the true age of a family (due to the neglected effect of ejection velocities).
• Figure 3: The estimated parent body diameters and formation ages of families reported in this catalog. See Sections 2.5 and 2.6 for the method used to determine these parameters. The color indicates $f=(D_{\rm LM}/D_{\rm PB})^3$ where $D_{\rm LM}$ and $D_{\rm PB}$ are the estimated largest-member and parent-body diameters, respectively. The families produced by the cratering collisions appear as dark blue dots; the catastrophic breakups with $f<0.5$ are shown in red.