Asteroid 6 Hebe: The probable parent body of the H‐type ordinary chondrites and the IIE iron meteorites

Abstract

Abstract-The S(1V)-type asteroid 6 Hebe is identified as the probable parent body of the H-type ordinary chondrites and of the IIE iron meteorites. The ordinary chondrites are the most common type of meteorites falling to Earth; but prior to the present study, no large mainbelt source bodies have been confirmed. Hebe is located adjacent to both the V6 and 3:l resonances and has been previously suggested as a major potential source of the terrestrial meteorite flux. Hebe exhibits subtle rotational spectral variations, indicating the presence of some compositional variations across its surface. The silicate portion of the surface assemblage of Hebe is consistent (both in overall average and in its range of variation) with the silicate components in the suite of H-type chondrites. The high albedo of Hebe rules out a lunar-style space weathering process to produce the weakened absorption features and reddish spectral slope in the S-type spectrum of Hebe. Linear unmixing models show that a typical Ni-Fe metal spectrum is consistent with the component that modifies an H-chondrite spectrum to produce the S-type spectrum of Hebe. On the basis of the association between the H chondrites and the IIE iron meteorites, our model suggests that large impacts onto the relatively metal-rich H-chondrite target produced melt bodies (sheets or pods) that differentiated to form thin, laterally extensive near-surface layers of Ni-Fe metal. Fragments of the upper silicate portions of these melt bodies are apparently represented by some of the igneous inclusions in H-chondrite breccias. Alternately, masses of metal could have been deposited on the surface of Hebe by the impact of a core or core fragment from a differentiated parent body of H-chondrite composition. Subsequent impacts preferentially eroded and depleted the overlying silicate and regolith components, exposing and maintaining large masses of metal at the optical surface of Hebe. In this interpretation, the nonmagmatic IIE iron meteorites are samples of the Ni-Fe metal masses on the surface of Hebe, whereas the H chondrites are samples from between and/or beneath the metal masses.

Surface composition and taxonomic classification of a group of near-Earth and Mars-crossing asteroids

“…The main belt asteroid 6 Hebe, which is located at 2.426 AU between the ν 6 secular resonance and the 3:1 mean motion resonance, shows spectral characteristics and mafic silicate compositions consistent with those of H chondrites (Gaffey, 1996;Gaffey and Gilbert, 1998), making of this asteroid its probably parent body. Cosmic ray exposure ages (CRE) of H chondrites indicate that their parent body, or a fragment of it, experienced multiple collisional events, occurred ∼ 60, ∼ 33 and ∼ 8 million years ago (Graf and Marti, 1995).…”

3D shape of asteroid (6) Hebe from VLT/SPHERE imaging: Implications for the origin of ordinary H chondrites

“…Indeed, Hebe's spectral properties and close proximity to orbital resonances in the asteroid belt make it a possible main source of ordinary H chondrites (i.e., ∼34% of the meteorite falls, Hutchison 2004;Farinella et al 1993;Migliorini et al 1997;Gaffey & Gilbert 1998;Bottke et al 2010). It was further proposed that Hebe could be the parent body of an ancient asteroid family (Gaffey & Fieber-Beyer, 2013).…”

Anatomy of a Partially Differentiated Asteroid: A “NEAR”-Sighted View of Acapulcoites and Lodranites

“…commun. ), ordinary chondrites (H, L, and LL) (Gaffey and Gilbert 1998), and 433 Eros (Murchie and Pieters 1996). Primitive achondrites, which have pyroxene/olivine ratios ranging from ∼1.9 to ∼0.4, should have band area ratios ranging from ∼1.5 to ∼0.5, respectively (Cloutis et al 1986).…”

“…commun.). The estimated ordinary chondrite fields are taken from Gaffey and Gilbert (1998). Eros parameters are taken from Murchie and Pieters (1996) and are for a pyroxenerich hemisphere, an olivine-rich hemisphere, and an average composition.…”