Earth, Moon, and Planets

, Volume 92, Issue 1, pp 261-277

First online:

Proton Irradiation of Centaur, Kuiper Belt, and Oort Cloud Objects at Plasma to Cosmic Ray Energy

  • John F. CooperAffiliated withRaytheon Technical Services Company LLC, SSDOO Project, NASA Goddard Space Flight Center
  • , Eric R. ChristianAffiliated withOffice of Space Science, NASA Headquarters
  • , John D. RichardsonAffiliated withCenter for Space Research, Massachusetts Institute of Technology
  • , Chi WangAffiliated withCenter for Space Research, Massachusetts Institute of TechnologyLaboratory for Space Weather, Chinese Academy of Sciences

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Times for accumulation of chemically significant dosages on icy surfaces of Centaur, Kuiper Belt, and Oort Cloud objects from plasma and energetic ions depend on irradiation position within or outside the heliosphere. Principal irradiation components include solar wind plasma ions, pickup ions from solar UV ionization of interstellar neutral gas, energetic ions accelerated by solar and interplanetary shocks, including the putative solar wind termination shock, and galactic cosmic ray ions from the Local Interstellar Medium (LISM). We present model flux spectra derived from spacecraft data and models for eV to GeV protons at 40 AU, a termination shock position at 85 AU, and in the LISM. Times in years to accumulate dosages ∼100 eV per molecule are computed from the spectra as functions of sensible surface depth less than one centimeter at unit density.The collisional resurfacing model of Luu and Jewitt is reconsidered in thecontext of depth-dependent dosage rates from plasma, suprathermal,and higher energy protons, and global exposure, by micrometeoroiddust grain impacts, of moderately irradiated red material below athin crust of heavily irradiated neutral material. This material should be more visible on dynamically `cold’ objects in the ∼40 AU region.