PowerPointPrsentation

1
A NEW MODEL OF INTERPLANETARY METEOROIDS BASED
ON LONG-TERM ORBITAL EVOLUTION
Valeri Dikarev1,2, Eberhard Grün1,3 Markus
Landgraf 4 1Max-Planck-Institut für Kernphysik,
Heidelberg, Germany ? 2Astronomical Institute
of St.Petersburg University, Russia ?
3University of Hawaii, USA ? 4ESOC, Darmstadt,
Germany
Abstract We construct a new meteoroid model that
replaces the models by Divine (1993) and Staubach
Grün (1995). Our approach of describing the
interplanetary dust cloud, however, is different
from that of our predecessors. Instead of
empirically found distribution functions, we use
distributions that are determined by orbital
evolution of various dust populations. The
populations correspond to expected structures in
zodiacal cloud. We determine the distributions of
meteoroid-sized debris dispersed along the orbits
of the parent bodies, comets and asteroids,
meteoroids residing in the torus of debris
scattered by Jupiter, and the distributions of
small dust grains spiraling towards the Sun under
the Poynting-Robertson drag from their parent
bodies, including scattered meteoroids. The
interstellar dust particles are represented by a
physical model as well. Each distribution
function has an arbitrary normalization factor
corresponding to the unknown dust production rate
for the population. We use several data sets to
validate the approach and to infer the population
normalisation factors minimizing model residuals
interplanetary meteoroid size distribution
observed at 1 AU, COBE DIRBE infrared
observations, Galileo Ulysses DDS in-situ
impact counts, particle fluxes derived from the
Helios 1 and Pioneer 10 and 11 dust experiments,
and AMOR radar meteor survey.
A population of scattered meteoroids
To-date catalogues of minor bodies are subject to
observational selection effects, and they may not
represent all sources of dust particles. In order
to compensate for incompleteness of the
catalogues, we introduce an independent
population of big meteoroids located in Jupiter
scattering zone. They are distributed in orbital
elements so as the steady-state model of close
encounters suggests, that is after multiple
encounters that erase memory of the initial orbit
except the Tisserand constant. These meteoroids
represent the unaccounted or relict sources of
particles. They generate dust through mutual
collisions, and the dust drifts toward the Sun
under the Poynting-Robertson effect. This
population is designed to fit to rather wide
latitudinal number density profile inferred from
the IRAS and COBE infrared observations.
Mass ranges and the dominant effects
Inventory of zodiacal cloud
Population distributions are not separable
Macroscopic bodies like comets and asteroids are
sources of dust, they generate particles of a
wide range of masses. Orbits of small dust grains
then evolve due to the Poynting-Robertson effect.
Orbits of big meteoroids either stay constant
until collisions grind them into small dust
grains, or get pulled by Jupiter, if close
encounters were possible, and serve as dust
sources at the new orbits.
Earlier meteoroid models adopted mathematical
separability of the distribution function in
orbital elements. However, physical models of the
sources and evolution of dust in zodiacal cloud
do not support separability. Semimajor axis
eccentricity scatter plots of comets (left) and
the dust from comets spiraling toward the Sun
under the Poynting-Robertson drag (right)
illustrate the true non-separable distributions.
Two- and three-dimensional arrays of distribution
function values replace the old one-dimensional
tables of the Divine and Staubach meteoroid
models.
A new interstellar dust flow model
At the present time, interstellar dust particles
are represented in our model by the Staubach
population or particles passing through the solar
system along straight lines. Replacement of this
approximation is on our to-do list, and the new
model should account for gravitational focussing
of large interstellar particles (left) and
defocussing of small interstellar particles by
the solar radiation pressure (right). It will
also account for the time variability of the
interstellar dust flux due to the Lorentz force
at its entrance to the solar system.
Please address your comments, questions and
criticism to Valeri Dikarev, dikarev_at_galileo.mpi-h
d.mpg.de.