IMEM2: a meteoroid environment model for the inner solar system

Context. The interplanetary dust complex is currently understood to be largely the result of dust production from Jupiter-family comets, with contributions also from longer-period comets (Halley- and Oort-type) and collisionally produced asteroidal dust. Aims. Here we develop a dynamical model of the interplanetary dust cloud from these source populations in order to develop a risk and hazard assessment tool for interplanetary meteoroids in the inner solar system. Methods. The long-duration (1 Myr) integrations of dust grains from Jupiter-family and Halley-type comets and main belt asteroids were used to generate simulated distributions that were compared to COBE infrared data, meteor data, and the diameter distribution of lunar microcraters. This allowed the constraint of various model parameters. Results. We present here the first attempt at generating a model that can simultaneously describe these sets of observations. Extended collisional lifetimes are found to be necessary for larger (radius ≥ 150 μm) particles. The observations are best fit with a differential size distribution that is steep (slope = 5) for radii ≥ 150 μm, and shallower (slope = 2) for smaller particles. At the Earth the model results in ~ 90–98% Jupiter-family comet meteoroids, and small contributions from asteroidal and Halley-type comet particles. In COBE data we find an approximately 80% contribution from Jupiter-family comet meteoroids and 20% from asteroidal particles. The resulting flux at the Earth is mostly within a factor of about two to three of published measurements.

The Distribution of Asteroidal Dust in the Inner Solar System

In this paper we demonstrate how the action of secular resonances near the inner edge of the asteroid belt strongly effects the inclinations and eccentricities of asteroidal dust particles, such that they lose the orbital characteristics of their parent body and are dispersed into the zodiacal background. As a consequence, it may not be possible to relate the distribution of interplanetary material at 1 AU to given asteroidal or cometary sources with the level of confidence previously imagined.

Estimating the Asteroidal Component of the Zodiacal Cloud using the Earth's Resonant Ring

The Earth's resonant ring is populated primarily by asteroidal dust particles because cometary particles have higher Poynting-Robertson drag rates and the Earth's resonances are not strong enough to trap them (Gomes, 1995). It has been shown that asteroidal particles in a limited size range from 5 — 30μm are responsible for the observed trailing/leading flux asymmetry caused by the trailing dust cloud embedded in the ring (Jayaraman and Dermott 1995). The magnitude of the flux asymmetry is a direct function of the area of dust in the ring, which in turn depends upon the number of asteroidal particles in the zodiacal cloud. Using a dynamical model of the ring and the background zodiacal cloud and estimating the surface area of dust needed in the ring to match the observed flux asymmetry in the 25 micron COBE waveband, we have calculated the fraction of asteroidal dust in the zodiacal cloud as a function of p, the slope of the size-frequency distribution of particles.

SIRTF: A Unique Opportunity for Probing the Zodiacal Cloud

The Space Infrared Telescope Facility (SIRTF) is planned for launch by NASA in 2001 in a heliocentric orbit at 1.01 AU The spacecraft will drift away from the Earth slowly, reaching a distance of 0.3 AU behind the Earth at the end of its 2.5 year mission. This implies that SIRTF will spiral through the Earth's resonant dust ring (Wright et al., 1995) and, in particular, that it will traverse the dust cloud in the ring that trails the Earth in its orbit. We have used a dynamical model of the ring (Dermott et al., 1994) followed by simulation of the SIRTF orbit to predict the variations in the zodiacal thermal emission due to the trailing dust cloud as seen by SIRTF. Because the dust ring is inclined to the ecliptic, the latitude of peak flux of the trailing cloud will have yearly oscillations about the ecliptic. The amplitude of the oscillations will increase as SIRTF approaches the cloud, reaching a maximum of 20 during the mission. The magnitude of the flux variations can be as high as 4 – 5% or 2–3 MJy/Sr, SIRTF's measurements of these effects will allow us to model the number density and thermal characteristics of asteroidal dust particles near the Earth.

Size Distributions of Asteroidal Dust: Possible Constraints on Impact Strengths

We present results of a numerical collisional model which shows that the slope index of the equilibrium size distribution is dependent upon the size-strength scaling properties of the colliding bodies. This implies that individual asteroid families or distinct taxonomic classes within the mainbelt asteroid population may evolve different equilibrium size distributions. Well constrained observations of the size distribution over particular size ranges may allow constraints to be placed on the impact strengths of particles much larger or smaller than are capable of being measured in laboratory impact experiments.