Introduction

The aim of this research is to better understand the dynamical behaviour of asteroidal dust particles over a wide range of particle sizes. Our previous attempts to model the orbital evolution of these particles using RADAU [1], a fifteenth order numerical integrator with variable time steps, were limited to particles with diameters less than 100/.¿m [2], This is because the orbits of interplanetary dust particles with diameters greater than this decay into the Sun, under the influence of Poynting-Robertson and solar-wind drag, on time scales of the order of millions of years or longer [3]. This puts any numerical investigation of the dynamical behaviour of a reasonably numerous (hundreds to thousands) distribution of large dust particles beyond the reach of currently available computational resources, when using traditional integration techniques. However, empirical evidence, such as the LDEF (Long Duration Exposure Facility) cratering record [4], strongly suggests the existence of a significant population of large interplanetary dust particles (100 ¡xm diameter and greater) near 1 AU, implying that particles with diameters as large as 500 fim may be significant sources of the infrared flux that we receive from the asteroid belt [5]. It is therefore important to extend our current models of the zodiacal cloud to include this large particle population.

To overcome this problem, we have developed a unique integration code specifically designed for evolving the orbits of large populations of dust particles under the effects of radiation pressure, Poynting-Robertson drag and solar-wind drag, as well as point-mass gravitational forces. To achieve this, we have applied the dissipative mapping technique introduced by Malhotra [6] to the specific problem of deriving a MVS (Mixed Variable Symplectic) type integration code [7] that also incorporates the effects of these non-gravitational forces [8]. The development and testing of this dissipative code is described in detail elsewhere [9]. This new integration code is significantly faster than more conventional integration techniques and will allow us to investigate, for the first time, the dynamics of asteroidal dust particles with diameters up to 500 pm or even larger.

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