Astron. Astrophys. 329, 785-791 (1998)

1. Introduction

Meteoroid detectors on board Pioneer 10 and 11 recorded a near constant rate of impact by dust grains, which have moderately eccentric orbits with random inclinations, out to a distance of 18AU (Humes 1980). Recent space probes such as Ulysses and Galileo, furthermore, detected dust grains in the ecliptic plane at heliocentric distances between 0.7 and 5.4 AU, and in an almost perpendicular-plane from ecliptic latitude to (Grün et al. 1995a,b). Although these dust grains may originate from different sources of interplanetary dust, the variation of the impact flux of meteoroids with heliocentric distance suggests the existence of dust sources in the outer Solar System.

Active comets can be major contributors to these dust grains. However, since small dust grains released from active comets are likely to have large eccentricities, most of them escape from the Solar System due to solar radiation pressure forces (Mukai 1985). Therefore it is unlikely that active comets are a major source of interplanetary dust at large heliocentric distances.

Recently, it has been suggested that significant dust production occurs in the Edgeworth-Kuiper Belt due to the mutual collisions of Edgeworth-Kuiper Belt objects (EKOs) (e.g. Backman et al. 1995; Liou et al. 1996; Stern 1996). Jewitt & Luu (1995) estimated that about objects with diameters larger than 100km exist in the Edgeworth-Kuiper Belt. Observations by the Hubble Space Telescope suggest that there are more than 2 Halley-sized objects in the region (Cochran et al. 1995). Duncan et al. (1995) estimated that, within 50 AU, the total number of comets in the Belt is roughly . It has been proposed that the collisions between these objects provide a significant amount of dust grains in the Edgeworth-Kuiper Belt. Stern (1996) estimated the production rate of collisional debris, and predicted a time-averaged mass supply rate of g yr^-1, for collisional debris ranging from multi-kilometer blocks to fine dust.

The in situ measurements by the Ulysses spacecraft show that the stream of interstellar grains penetrates into the Solar System (Grün et al. 1993). In this paper, we propose that the impacts by such interstellar dust on EKOs produce a considerable amount of dust grains. EKOs are continuously bombarded by interstellar dust grains with high relative velocities ( km s^-1). Although the amount of target material excavated by the individual impacts of interstellar dust is smaller than the amount produced by collisions between large EKOs, impacts by interstellar dust grains occur more frequently. Moreover, all EKOs are bombarded by interstellar dust simultaneously, whereas mutual collisions of EKOs occur locally. As a consequence, the continuous impact by interstellar dust should provide a considerable amount of dust grains all over the Edgeworth-Kuiper Belt region.

In Sect. 2, we investigate dust production under two different surface conditions. In one model the surfaces are composed of hard icy material. In the other model the surfaces are covered by loose icy particles, produced by collisional resurfacing of EKOs. In Sect. 3 the total dust production rate over the entire Edgeworth-Kuiper Belt is calculated by using the same size distribution of EKOs modelled by Stern (1996). Our results are compared with the production rate of collisional debris predicted by Stern (1996) in Sect. 4. A summary of our results is presented in Sect. 5.

© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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