Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS): Establishing Asteroid-Meteorite Connections Between Hungaria Asteroids and Meteorites of the Acapulcoite-Lodranite Clan

Hungaria region asteroids are survivors of giant planet migration that destabilized a now extinct inner-portion of the primordial asteroid belt. In this scenario, the Hungaria region represents a “purgatory” for the closest, preserved samples of material from which the terrestrial planets accreted. Deciphering the surface composition of these samples may provide constraints on the nature of the primordial building blocks of the terrestrial planets. We carried out a two-phased ground-based observational campaign—Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS)—to record their visible and near-infrared reflectance spectra. We analyzed these spectra to characterize the taxonomy, surface mineralogy, and potential meteorite analogs of Hungaria background and family asteroids. In HARTSS I we found that ~80% of the background population are stony S-types that exhibit spectral and mineralogical diversity. Two main asteroid-meteorite connections exist between background S-types and stony meteorites: unmelted L-/LL-ordinary chondrites, and partially-melted primitive achondrites. To strengthen connections between S-types and partially-melted meteorites, we measured the spectral and cosmochemical properties of 10 acapulcoite-lodranites. We found a well-defined relationship between the ~2 μm band center and ferrosilite (Fs) content of orthopyroxene. Because Fs in orthopyroxene and fayalite (Fa) content in olivine are well-correlated in these meteorites, the derived Fs content can be used to estimate Fa of the co-existing olivine. These relationships help to determine whether S-types are nebular (ordinary chondrites), or have experienced partial melting (primitive achondrites). In HARTSS II, we focus on family members and hypothesize that the Hungaria family is compositionally homogeneous. Surviving fragments of an asteroid collisional family typically exhibit similar taxonomies, albedos, and spectral properties. Measurements of these properties for Hungaria family members are consistent with this scenario. Spectral observations of 92 Hungarias acquired during HARTSS uncover a compositionally heterogeneous background population and a spectrally homogeneous collisional family, implying that the parent body was homogeneous. This parent body was likely consistent in composition with enstatite achondrites (aubrites) and therefore formed under reduced, igneous conditions. If aubrites are truly representative of igneous mantle material, then the Hungaria parent body was itself a collisional fragment that originated on a differentiated, heterogeneous parent body early in Solar System history.