Kalliope sings rock and metal

ABSTRACT Asteroid (22) Kalliope is the densest known asteroid in the main belt, with a density of $\rho = 4.4 \pm 0.46$ g cm$^{-3}$, suggesting that it is differentiated. Kalliope has recently been identified as the parent body of a family of collisional fragments, which is located in the so-called ‘pristine zone’ of the outer main belt, between 2.825 and 2.955 au. Kalliope’s spectroscopic classification has been uncertain, but it has been broadly associated with iron meteorites. We combined visible reflectance spectra from the Gaia Data Release 3, visible SDSS spectrophotometry, and new near-infrared spectroscopic observations from the SpeX instrument at NASA’s Infrared Telescope Facility for 22 Kalliope family members, which were mostly classified as X or Xk-types. Considering the spectral slope and 0.9 $\,\mathrm{\mu }\mathrm{m}$ absorption band variations, we divided the family members into three spectral groups. By analysing the spectra and geometric visible albedo data, we identified the best matches for Kalliope family members as iron and pallasite meteorites. The absence of crustal material among family members makes the nature of Kalliope’s parent body unclear, whether it was a fully or partially differentiated planetesimal and whether it originated in the inner or outer Solar system.