Searching for primitive, dark, spectrally red asteroid families in the main belt with Gaia

TL;DR

This study uses Gaia DR3 VIS reflectance spectra to characterize central and outer main-belt asteroid families within the C-/X-complex, aiming to identify the reddest families that may be T- or D-type and potential NEA sources. Through interloper removal, albedo screening, and robust averaging of Gaia spectra (with reddening corrections) plus Bus-DeMeo template classification and PCA, eight reddest families emerge as strong T-/D-type candidates, suggesting possible delivery to the NEA population via Jupiter resonances such as 5:2J and 2:1J. However, the Gaia-based classifications are not definitive, as some results depend on catalogue (NES15 vs AFP25) and small-number statistics; thus, the authors call for follow-up near-infrared observations to confirm the red classifications and distinguish between T- and D-type. The work advances our understanding of primitive, dark asteroid family members and their potential links to NEA populations, highlighting resonance pathways as plausible source regions for red-sloped asteroids.

Abstract

Dark asteroids with featureless neutral to red spectra are of particular interest due to their ability to potentially harbour primitive, hydrated, and possibly organic-rich material. These asteroids belong to the spectroscopic C-complex, to the X-types with low geometric visible albedo values as well as to the T- and D-type end members of the Bus-DeMeo spectroscopic taxonomy. Here we used Gaia Data Release 3 visible reflectance spectra to study the average spectral profiles of the C- and X-complex asteroid families in the central and outer main belt (orbital semi-major axis between 2.5 - 3.7~au). We found that eight of these families, namely 96 Aegle, 627 Charis, 1484 Postrema and 5438 Lorre, previously classified as C-complex families, and 322 Phaeo, 1303 Luthera, 5567 Durisen and 53546 2000BY6 previously classified as X-complex families, have redder slopes than implied by their previous classification and could be better classified as T-/D-type families. Some of these families may also feed the near-Earth asteroid population, being responsible for the observed T-/D-type excess. However, the analysis of their principal components of Gaia Data Release 3 spectra suggest that further near-infrared observations are needed in order to verify this identification.

Figures (14)

• Figure 1: Average reflectance spectra of the reddest asteroid families using Gaia DR3. The spectra are normalised at 0.55 µm and shifted on the y-axis by 0.5 between families for clarity. Where available, the average SDSS reflectance spectra are over-plotted.
• Figure 2: Location of the eight reddest families in the PC1-PC2 space in relation to the location of the C-complex, X-complex and D-type asteroids (depicted using KDE contours) with crosses and diamonds corresponding to NES15 and AFP25 catalogues respectively.
• Figure 3: Proportion of NEA source regions. The top bar depicts the breakdown of sources for all NEAs in MP3C, and the bottom bar depicts the breakdown for the T-/D-type NEAs using only spectroscopic observations.
• Figure 4: Albedo distribution of T-/D-type NEAs. The dark grey bars represent NEAs that have been classified using either photometric or spectroscopic observations, and the light grey bars represent NEAs that have been classified using only spectroscopic observations.
• Figure 5: Location of the eight T-/D-type families in the proper semi-major axis vs. proper inclination space. The MMRs with Jupiter and the secular resonance with Saturn are shown as dashed lines. The red points show the very red families (from NES15), with the family number indicated.