Description
In the classical theory of planetesimal differentiation, a body would form an iron-rich core, an olivine-dominated mantle, and a pyroxene-rich basaltic crust. The detection of differentiated bodies in the current asteroid main belt will allow us to get insights and study the very initial phases of planetesimal accretion.
Asteroid (22) Kalliope is the densest known asteroid with ⍴=4.4±0.46 g.cm-3 indicating a metal-rich composition. The low radar albedo (0.18±0.05), however, points towards a lower metal content on the surface but the presence of very high density indicates a differentiated metal-rich interior.
(22) Kalliope is the parent body of an asteroid family in the outer main belt consisting of 302 members. Therefore, studying the physical properties of the Kalliope family members we can get insights into the internal structure of the original planetesimal.
Thirty seven Kalliope family members have visible reflectance spectra from Gaia DR3 and 22 of which were observed at NASA IRTF obtaining their near-infrared spectra. Using the reflectance spectra of Kalliope family members as well as their geometric visible albedos we matched them with meteorites that are included in the RELAB and PSF meteorite lab spectra databases.
We discovered that the Kalliope family is the first family that consists of metallic and stony-metallic fragments, confirming the differentiated nature of the original planetesimal.
