Coloration and darkening of methane clathrate and other ices by charged particle irradiation: Applications to the outer solar system

摘要: Methane clathrate is expected to be an important carbon-containing ice in the outer solar system. We investigate effect of electron irradiation by coronal discharge on several simple hydrocarbons enclathrated or mixed with H2O H2O+NH3 simulation effects wind, planetary magnetospheric particles, and cosmic rays surfaces containing these ices system interstellar space. H2O+CH4 clathrate, H2O+C2H6, H2O+CH4+NH3, H2O+C2H6+NH3, H2O+C2H2 are all initially white ices, produce yellowish brownish organic products upon charged particle irradiation. Significant coloration occurs doses 109 erg cm−2, corresponding short interplanetary times. Uranian electrons penetrate ∼1 mm depth deposit this dose 8, 30, 65, 200, 500 years into Miranda, Ariel, Umbriel, Titania, Oberon, respectively. Further laboratory surface results a progressive darkening more subdued color. For conversion efficiency solids G ≃ 1 molecule keV−1, upper limit for time total destruction CH4 other 5 × 104 (Miranda) 3 106 (Oberon). Remote detection possible only when its replenishment rate exceeds at probed spectroscopy. Reflection spectroscopy irradiated frost compared spectra objects relevant inorganic materials. Ultraviolet-visible infrared transmission postirradiation residues presented. Persistence color bands Triton Pluto suggests ongoing activity and/or atmospheric haze. Over 4 year scales, ≥ 10 m satellite cometary material processed radiation-hardened ice-tholin mixture devoid CH4. Preaccretional chemistry, exogenous materials, endogenous chemistry contribute spectral properties icy satellites which accreted CH(O) molecules. Radiation traces deposition mobilized impact-exposed carbon-bearing volatiles satellites. More exhaustive experiments necessary work out detailed relationships between initial composition, exposure age, color/albedo.