Primitive asteroids in the main belt, Cybele, and Hilda populations from Gaia DR3

TL;DR

This study leverages Gaia DR3 spectrophotometry to quantify the abundance and properties of primitive D-, Z-, and P-type asteroids from the inner main belt to the outer solar system, including Cybele and Hilda populations. By enforcing a SNR$>20$ cut, an albedo threshold ($p_v<12 ext{~%}$), and cross-validating with Bus-DeMeo and Mahlke taxonomies via χ^2 fits and visual checks, the authors derive detailed slope and size distributions. They find a pervasive but distance-dependent presence of D-/Z-types in the main belt, with a pronounced rise in Cybele, Hilda, and especially Trojans, and conclude that D- and Z-types likely originate from outer Solar System reservoirs, while P-types show evidence of in-situ formation in some regions. The results, complemented by comparisons to comets and Martian moons, suggest a complex dynamical history with implantation and resurfacing processes shaping visible spectra, and highlight Gaia DR3’s power in linking asteroid taxonomy to Solar System evolution.

Abstract

Primitive asteroids include C-, P-, and D-classes, known to be dark and having spectra mostly featureless. They differ in the spectral slope, which ranges from moderate values for C-types, and progressively increases in P- and D-types, the latter being the reddest. While C- and P-types are commonly observed in the asteroid main belt, D-types are commonly found further from the Sun, in the Cybele, Hilda, and Jupiter Trojans regions, and very few are reported in the main belt. This study aims at characterizing the abundance of primordial and red asteroids, belonging to the P-, D-, and Z-classes in the Mahlke et al. (2022) taxonomy, in the 2-5.2 AU region using the third data release by the Gaia mission spectral catalog, which includes more than 60000 spectrophotometric data of asteroids. We have applied the following methodology to identify primordial asteroids in the catalog: 1) selection of objects with signal to noise ratio greater than 20; 2) albedo value less than 12%; 3) chi-squared fit to automatically identify potential D-, Z-, and P-types using Bus-DeMeo and Mahlke taxonomy; 4) visual inspection of every spectrum to confirm the taxonomic classification. Referring to Mahlke taxonomy, we have found 318 new D-types across the main belt, as well as 124 Z-types, and is in agreement with theoretical estimations. We computed the spectral slope in the visible range (0.55 - 0.81 μm). We also have identified 265 P-types in the main belt. For the Cybele and Hilda asteroids, we characterize the taxonomic class of all the bodies with SNR higher than 20 in the Gaia catalog, for a total sample of 193 and 180 asteroids, respectively.

Figures (34)

• Figure 1: Distribution of the SNR for the entirety of Gaia's catalog (left panel) and for the retrieved dataset (right panel) composed of D-, Z-, and P-types. The red lines represent the SNR threshold at 20.
• Figure 2: Histogram of the spectral slope distribution for (from left to right) P-, D-, and Z-types in the main belt. The bin size is of 1 $\%/1000$ Å.
• Figure 3: Spectrum of (900) Rosalinde from the Gaia spectral catalog. The filled blue region represents the mean spectrum of Mahlke's D-type.
• Figure 4: Diameter as a function of the semi-major axis. The D-types are represented by blue dots, while Z-types are shown with red triangles.
• Figure 5: Inclination as a function of the semi-major axis for P-types in the main belt. Symbol size is proportional to the diameter. The colorbar represents the spectral slope. The red line is the $\nu_6$ secular resonance position in this space morbidelli2010.