Ice sublimation of dust particles and their detection in the outer solar system

Hiroshi Kobayashi,Satoru Yamamoto,Hiroshi Kimura,Sei-Ichiro Watanabe,Tetsuo Yamamoto

doi:10.5047/eps.2009.03.001

Abstract

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 10–50AU for Voyager and at 5–15AU 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 15–40AU for Voyager and 5–20AU 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.

Highlights

Edgeworth-Kuiper belt objects are the least processed icy bodies that are located in the Edgeworth-Kuiper belt (EKB) currently at 30–50 AU from the sun
Theoretical studies indicate that timescales for dust particles released from EKBOs to drift inward by the Poynting-Robertson (P-R) effect are shorter than their timescales against collisional destruction in the outer solar system if their radii are smaller than ∼10 μm (Liou et al, 1996)
The dust production rate of dust particles with radii smaller than 20 μm by mutual collisions between EKBOs has been estimated at Mdust = 1 × 105 g s−1–4 × 107 g s−1 by Yamamoto and Mukai (1998), adapting the collisional parameter used by Stern (1996)

Summary

Introduction

Edgeworth-Kuiper belt objects are the least processed icy bodies that are located in the Edgeworth-Kuiper belt (EKB) currently at 30–50 AU from the sun. We expect the difference of the fluxes measured by these spacecraft may be explained by the size distribution of dust particles drifting from the EKB because the spacecraft have different detection size threshold. If such icy dust particles drift inward by the P-R effect, the ice component in the particles intensively sublimes when their temperatures become about 100 K (Kobayashi et al, 2008).

Results

Conclusion