Two faces of L-type asteroids

Context. L-types are a rare class of asteroids whose spectra indicate similarities with CO and CV chondrites, suggesting high abundances of refractory inclusions, particularly with respect to the calcium-aluminium-rich inclusion. This implies that their parent bodies were among the earliest chondrites to form. Aims. We aim to identify L-types within selected asteroid families and to provide the first UV-VisNIR spectral characterisation of asteroids in this class. We further assess the spectral variability among L-types and evaluate the suitability of ESA Gaia UV-visible spectra for their identification. Methods. We obtained VLT/X-shooter spectra of nine asteroids associated with L-type families. We classified them taxonomically using their UV-VisNIR spectra combined with the visual albedo and compared them to Gaia spectra and to ordinary, CO, and CV chondrites. Results. Among the nine asteroids, we identified four L- and two M-types (Mahlke taxonomy), exhibiting diverse spectral features. Placing them into context of other L-types and known Barbarians using literature data, we find that L-types cluster into two groups based on spectra and albedo. One group depicts a deep 2 μm absorption and is denoted LL, while a second group shows a shallow or absent 2 μm feature and is denoted LM. We find a similar bimodality among CO and CV chondrites. Their steep UV-visible slopes and 1 μm features enable us to distinguish L- from S-types in Gaia’s spectral range. Conclusions. The expanding census of L-types reveals a dispersed, possibly bimodal spectral distribution across multiple families, indicative of heterogeneity of the CO and oxidised CV chondrites parent bodies. Both the Aquitania and Brangäne family appear to come from such heterogeneous planetesimals. The Watsonia family is uniform and best represented by reduced CV chondrites. On the other hand, L-types with profound 2 μm absorptions such as (234) Barbara appear to be unsampled in the meteorite collection. Upcoming Gaia DR4 spectra and the ongoing SPHEREx mission will offer deeper insights into the distribution and mineralogical properties of this enigmatic class.