Abstract

624 Hektor, the largest Jovian Trojan, is a D-type asteroid. We have observed the reflectance spectrum of Hektor from 2.4 - 3.6 um, with the UKIRT/CGS4, and with other data we have constructed the spectrum from 0.3 to 3.6 um. The geometric albedo rises from 0.023 at 0.44 um to 0.065 at 2.5 um, and remains nearly constant out to 3.6 um. Hektor shows no indication of the strong 3-um absorption band seen in the spectrum of the low-albedo hemisphere of Iapetus and attributed to N-H in the surface materials (T. C. Owen et al., Icarus, in press, 2000). We have modeled the spectral geometric albedo using the Hapke scattering theory. Intimate mixture models consisting of Mg-rich pyroxene, kerogen, serpentine, and HCN polymer fit the spectrum well, except for a turn-up in the UV. The upper limit to water ice in these models is 4 wt. percent, but a significant fraction of the hydrous silicate serpentine is permitted. Other intimate mixture models without the HCN polymer similarly provide adequate fits, but also fail to show the UV turn-up. Spatially segregated models with Mg-rich pyroxene, kerogen, and serpentine also fit reasonably well. Models incorporating large amounts of olivine, or the meteorites Allende (CV3) and Murchison (CM2), do not fit. Hektor's large size and extremely elongated shape ( 2:1 axial ratio) suggest that it may be assembled from the collisional fusion of two "halves". Possible future space missions can search for spectral differences on different ends of this elongated object, and in craters that penetrate any mixed, global regolith.