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CHAPTER 34

Solar System Dust

Eberhard Grun ̈

Max-Planck-Institut f ̈ur Kernphysik

Heidelberg, Germany

Hawaii Institute of Geophysics and Planetology

Honolulu, Hawaii

1. Introduction 3. Dynamics and Evolution Bibliography


2. Observations 4. Future Studies

S

olar system dustis finely divided particulate matter
that exists between the planets. Sources of this dust
are larger meteoroids, comets, asteroids, the planets, and
their satellites and rings; there is interstellar dust sweeping
through the solar system. These cosmic dust particles are
also often called micrometeoroids and range in size from
assemblages of a few molecules to tenth- millimeter-sized
grains, above which size they are called meteoroids. Be-
cause of their small sizes, forces additional to solar and plan-
etary gravity affect their trajectories. Radiation pressure and
the interactions with ubiquitous magnetic fields disperse
dust particles in space away from their sources. In this way,
micrometeoroids become messengers of their parent bod-
ies in distant regions of the solar system. Because of their
small sizes, a tablespoon of finely dispersed micrometer-
sized dust grains scatter about 10 million times more light
than a singlemeteoroidof the same mass. Therefore, a
tiny amount of dust becomes recognizable, while the par-
ent body from which it derived may remain undetected.

1. Introduction

One of the earliest known phenomena caused by solar sys-
tem dust is the zodiacal light.Zodiacal lightis a promi-
nent light phenomenon that is visible to the human eye in
the morning and evening sky in nonpolluted areas (Fig. 1).
Already in 1683, Giovanni Domenico Cassini presented
the correct explanation of this phenomenon: It is sunlight

scattered by dust particles orbiting the Sun. The relation to

other “dusty” interplanetary phenomena, like comets, was

soon suspected. Comets shed large amounts of dust, visible

as dust tails, during their passage through the inner solar

system. The genetic relation between meteors and comets

was already known in the 19th century. Meteoroids became

the link between interplanetary dust and the larger objects:

meteorites, asteroids, and comets.

Cosmic dust can have different appearances in different

regions of the solar system. It consists not only ofrefractory

rocky or metallic material as in stony and iron meteorites,

but also ofcarbonaceous material; dust in the outer solar

system can even be ice particles.

Individual dust particles in interplanetary space have

much shorter lifetimes than the age of the solar system.

Several dynamic effects disperse the material in space and

in size (generally going from bigger to smaller particles).

Therefore, interplanetary dust must have contemporary

sources, namely, bigger objects like meteoroids, comets,

and asteroids in interplanetary space but also planetary

satellites and rings. In addition there are dust particles im-

mersed in the local interstellar cloud through which the

solar system currently passes that penetrate the planetary

system.

Dust is often a synonym for dirt, which is annoying and

difficult to quantify. This is also true for interplanetary dust.

Astronomers who want to observe extra–solar system ob-

jects have to fight separating the foreground scattered light

from the zodiacal light. Theoreticians who want to model

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