COMPOSITIONAL DIVERSITY AMONG HUNGARIA REGION ASTEROIDS: EVIDENCE FROM THE OBSERVATORY AND THE LABORATORY

The Hungaria region of ~14,000 small (D <11km) asteroids is a poorly understood population both compositionally and dynamically. These neighbors to the terrestrial planets are unique as they are found interior to the Main-belt and have resided in their current location since early in solar system history. Mars-crossing and near-Earth asteroids make closer approaches to the terrestrial planets, but they are dynamically short-lived (~10 Myr) “escapees” from the Main-belt. The planetesimals that originated in the terrestrial planet region were either accreted or scattered out early in solar system history, leaving the Hungarias as the closest remaining “survivors” of the asteroidal material from which the terrestrial planets accreted.

We have undertaken an observational campaign to record the near-infrared reflectance spectra of a sample of 42 (36 background; 6 family) Hungaria asteroids with absolute magnitudes (H) <16 to characterize their surface mineralogy through spectral band parameter measurements. By combining these telescopic data with spectral and geochemical data obtained in the laboratory from “free” asteroid samples that arrive to Earth as meteorites, we can establish connections between Hungaria asteroids and analogous meteorite groups.

We find evidence of three main meteorite-groups represented in the Hungaria region; 1) enstatite achondrites (i.e., aubrites), 2) ordinary chondrites (i.e., H, L, and LL), and 3) primitive achondrites (i.e., acapulcoites and lodranites). Five of the six Hungaria family members are spectrally consistent with the largest collisional fragment 434 Hungaria, which is widely considered to be related to fully-melted aubrite meteorites. Analyses of spectral band centers and band area ratios for 25 of 36 Hungaria background objects reveal evidence for two other meteorite groups. Published laboratory data for ordinary chondrites compared with our asteroid spectra point to the existence of unmelted L and LL chondrites in the region. Preliminary results from the laboratory analyses of our suite of 12 primitive achondrites indicate the existence of partially-melted primitive achondrites in the region as well. These asteroid-meteorite connections suggest that planetesimals in the Hungaria region have experienced varying degrees of petrologic evolution.