The flux of interplanetary dust beyond the Jupiter's orbit, which supposedly originates from Edgeworth-Kuiper belt, has been measured in situ by instruments on board Voyager and Pioneer spacecraft. The measured flux shows a nearly flat radial profile at 10-50 AU for Voyager and at 5-15 AU for Pioneer. Because the orbital evolution of dust particles controlled by radiation forces results in the flux that is inversely proportional to distance from the sun, dust particles detected by spacecraft should have suffered from other dynamical effects. We calculate model fluxes on the spacecraft taking into account the effect of ice sublimation as well as radiation forces on the orbital evolution of dust particles. Our results show that the radial profile of the model flux becomes relatively flat near the outer edge of the sublimation zone, where ice substantially sublimes. The expected location of the flat radial profile, which depends on the detection threshold of instruments, is 15-40 AU for Voyager and 5-20 AU for Pioneer. Because our model fluxes are comparable with the measured ones, we conclude that the flat radial profiles of the dust flux derived from in-situ dust impacts may be caused by ice sublimation.
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