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

The S(IV)-type asteroid 6 Hebe is identified as the probable parent body of the H-type ordinary chondrites and of the LIE 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 upsilon(6) and 3:1 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.