Laboratory spectroscopy of HED meteorites

4 Vesta is one of the largest and the most massive asteroid in the Main Asteroid Belt. This asteroid possesses a basaltic surface and apparently formed and differentiated very early in the history of the solar system. There are strong evidences that indicate Vesta as the parent body of Howardites, Diogenites and Eucrites (HEDs). HED meteorites are a subgroup of achondrite meteorites and they are a suite of rocks that formed at high temperature and experienced igneous processing similar to the magmatic rocks found on Earth. The visible and near-infrared (VNIR) reflectance spectra of Vesta's surface show high similarity with the laboratory spectra of HED meteorites. Vesta and HEDs spectra have two crystal field absorption bands close to 0.9 μm and 1.9 μm indicative of the presence of ferrous iron in pyroxenes. The HEDs differ from each other primarily based on variation in pyroxene composition and the pyroxene-plagioclase ratio as well as rocks texture characteristics (e.g., size of crystals). These differences suggest that a combined VNIR spectra studies of Vesta and HED meteorites might reveal the different characteristics of the surface compositions and shed new light on the origin and the thermal history of Vesta. Moreover the link between Vesta and HEDs could provide a test bed to understand the short-lived radionuclide-driven differentiation of planetary bodies. Here we present preliminary result of a study of spectral characteristics of different HED samples, provided to us by the Vatican Observatory. Bidirectional reflectance spectra of slabs of meteorites are performed in the VNIR, between (0.35/2.50) μm, using a Fieldspec spectrometer mounted on a goniometer, in use at the SLAB (Spectroscopy laboratory, INAF, Rome). The spectra are acquired in standard conditions with an incidence angle i=30o and an emission angle e=0o, measuring a spot with a diameter of 5 mm. Different Howardite, Diogenite and Eucrite samples are "mapped" considering several spots on the surface of the slabs to define their spectral variability between samples representing the different types of HEDs and to describe the spectral heterogeneity for each samples. A preliminary comparison with mineralogical and petrographic characteristics has been done describing hand samples and their thin sections. These data will be incorporated in a spectral library that could be an useful tool for the interpretation of data acquired by the Dawn mission in orbit on Vesta.