Jupiter Trojans spectrophotometry using Gaia DR3 catalog
Sonia Fornasier, Noemie El-Bez-Sebastien
TL;DR
Gaia DR3 visible spectrophotometry, complemented by extensive literature spectra, yields the largest visible-wavelength survey of Jupiter Trojans to date. The analysis shows a population dominated by D-type surfaces with a notable Z-class fraction, and a higher spectral diversity in the L4 swarm driven largely by dynamical families; after excluding peculiar families, L4 and L5 share similar average spectral slopes around $S_V \approx 9.3 \,\%/1000 \,\text{Å}$ and albedos of $p_V \approx 7.6\%$, implying a common origin, likely from the Transneptunian region, rather than two separate source regions. The observed color distribution is not bimodal, suggesting evolutionary processes such as space weathering and collisional resurfacing shape the surface properties. The results support a capture scenario from outer Solar System populations, with Lucy’s in-situ observations expected to provide decisive tests of surface composition and heterogeneity.
Abstract
We present the spectral characterization of Jupiter Trojans using data from the Gaia mission DR3 spectral catalog (320 spectra of good quality) and from the literature. Gaia spectrophotometry is available in 16 spectrophotometric points covering the 0.33-1.08 $μ$m range. The final dataset includes 519 Trojans, 291 in the leading swarm (L4) and 228 in the trailing swarm (L5), which we classified using the Bus-Demeo and Mahlke classification schemes. The Trojan population is dominated by featureless asteroids with red spectral slopes belonging to the D-type, and an important fraction ($\sim$ 40\%) belong to the Z-class (in Mahlke taxonomy), characterized by very red slopes. The L4 swarm shows a higher spectral variability and a higher amount, by a factor of 2, of less spectrally red asteroids belonging to the C, P, and X classes, mainly associated with families members. Once excluding peculiar families members the two swarms have very similar average slope and albedo values (7.86 $\pm$ 0.15\% and 7.35 $\pm$0.15\% for the L4 and L5 swarms, respectively). This points toward a common origin of the bodies of the two swarms, likely from the Transneptunian region. We do not observe a spectral color bi-modality distribution, conversely to the results previously reported in the literature. The spectral slope distribution, peaked at 9-11 \%/1000 Å, it is very narrow compared to that of Transneptunian objects (TNOs) or cometary nuclei. Trojans visible spectral slopes match those of the less red TNOs, and lack of extremely red and organic rich bodies. We suggest that the Jupiter Trojans might have been captured by Jupiter from the Centaurs and scattered disk population, and that the lack of extremely red objects among Trojans is due to removal of the organic-rich crust through the sublimation of volatiles and collisions as TNOs migrated inward in the Solar System.