ION IRRADIATION OF FROZEN METHANOL, METHANE, AND BENZENE: LINKING TO THE COLORS OF CENTAURS AND TRANS-NEPTUNIAN OBJECTS

摘要

We present visible and near-infrared (0.65-2.7 μm) diffuse reflectance spectra of frozen (16-80 K) methanol (CH_3OH), methane (CH_4), and benzene (C_6H_6), collected before and after irradiation with 200 keV H~+ and Ar~+ ions, and 400 keV Ar~(++) ions, up to a dose released to target molecule of about 350 eV per 16 amu. The results evidence a strong reddening and darkening of the spectra, due to the formation of an organic (C-rich) refractory residue. The spectral behavior is compared with some Centaurs and trans-Neptunian objects; we find that many icy objects in the outer solar system may have grown an irradiation mantle, produced by cosmic ion irradiation of simple hydrocarbons and/or alcohols.