Observations, compositional, and physical characterization of near-Earth and Mars-crosser asteroids from a spectroscopic survey

摘要

Aims. We analyse a significantly large sample ofspectroscopic data to provide a compositional characterization of thenear-Earth asteroid population. We present visible and near-infraredspectra of a total of 74near-Earth asteroids (NEAs) andMars-crossers (MCs), covering the wavelength region from0.5 to2.5m.Using spectra of NEAs from other databases to enlarge our sample, andcompiling two comparison samples of main belt asteroids (MBs) andordinary chondrites (OCs), we analyse a total of 79NEAs,91MBs, and 103OCs. Methods. We obtained our visible and near-infrared spectra usingthe instruments and the telescopes located at ``ElRoque de losMuchachos'' Observatory, in the island of LaPalma (Spain). Wecompute several diagnostic spectral parameters from the reflectancespectra of NEAs, MBs, and OCs, that are used to infer the mineralogicalcomposition. The distribution of the obtained values are analysed in2different parameter spaces. We also apply a robust statisticalmethod based on neuronal networks to those spectral parameters, tocompare the NEAs with OCs. Space weathering effects and dynamical andphysical properties of NEAs and MBs are also studied. Results. Compositional differences between MBs and NEAs areinferred from the mineralogical analysis. The most remarkable resultsare: (1)the high olivine content of the NEAs; (2)thecompositional similarity between NEAs and a small group of meteorites,the LLordinary chondrites; and (3)that NEAs are notcompositionally similar to OCs, implying that they are not the mostlikely parent bodies of those meteorites, as has been widely believed.Toexplain their apparently fresh surfaces (NEAs are on averageless red than MBs), acombination of composition and sizedistribution (NEAs have diameters of some kilometres) should beinvoked. Dynamical models applied to our sample of NEAs indicate thatmost of them originate in the inner part of the main belt,asexpected. Key words: minor planets, asteroids: general - methods: observational - techniques: spectroscopic - surveys