Dusty rings around all four
giant planets have been discovered by Voyager. Some dusty phenomena
were related to the dense rings, others to satellites, and still others
were found in isolation. In July of 2004 Cassini started its in-situ
investigation of the Saturn ring system – a few years after Galileo
performed its detailed study of the Jovian ring system. Models
(sometimes conflicting) have been developed to explain some properties
of a specific ring. With the in depth investigation of two dusty ring
systems and their environments it is time to reflect commonalities and
diversities in order to obtain a deeper understanding of this exciting
widespread astrophysical phenomenon. The workshop is intended to bring
together leading observers and modelers in order to provide a
stimulating environment for new ideas and amalgamation of diverse views.
Dense rings around Saturn and
Uranus were first observed from the ground while faint dust rings
around all giant planets have been discovered in recent years by
spacecraft. The first detections of dust clustered near the equatorial
planes of Jupiter and Saturn were accomplished a quarter-century ago by
pressurized ”beer-can” experiments aboard the Pioneer spacecraft. But
it was the flybys of the giant planets by the Voyager spacecraft that
showed the diversity and complexities of the ring systems. Some dusty
phenomena were related to the dense rings, others to satellites, and
still others were found in isolation. Radio occultation experiments
with the Voyager spacecraft showed that the dense rings consist of cm
to m sized particles, while dust rings are mostly composed of micron
sized particles. While the discoveries and early observations of dusty
rings were made by chance a much more systematic survey of Jupiter’s
and Saturn’s environs was and is planned for the Galileo and Cassini
missions.
Observational techniques used
to analyze circumplanetary dust rings are images, spectra, occultation
profiles, charged particle absorption signatures, and in-situ sampling
of ring dust. Since 1996 we have obtained detailed studies of the
Jovian ring system by the Galileo spacecraft including recent passages
through the ring system enabling us to analyze in-situ grains orbiting
the planet. In July 2004 Cassini will start its in-situ investigation
of the Saturn ring system and first observations will be made within a
years time. In recent years also ground- and space-based astronomical
observations over a wide of wavelengths of dust rings have been
possible providing additional information on these rings.
Several motivations provoke
interest in dusty rings. First, ring dynamicists are challenged by the
wide range of forces to which these grains are subject and by the
counter-intuitive behavior of some of this material. Second,
circumplanetary grains intimately interact with the surrounding
magnetospheric plasma and with neighboring satellites, in some cases
being derived from the latter and in others modifying those surfaces.
Thirdly, dust probes conditions in the surrounding magnetospheric
plasma and, through its response, calibrates the nature of those
fields.
The applicable physics and
dynamics acting on dusty rings are distinct from those pertinent to
interplanetary dust, because the dust orbits through a magnetosphere
and about a central mass other than the radiation source. But
circumplanetary dust particles are not classical ring particles either.
In the latter case, collisions dominate and the resultant structures
can be studied with the tools of fluid dynamics and kinetic theory. For
faint rings, collisions among ring particles are rare, and each
particle behaves as a miniature independent satellite circling its
primary; thus the methods of single-particle dynamics may be applied.
However, as constituent particles are generally tiny, non-gravitational
forces (electromagnetism, radiation and drag) must be included.
Dynamics of circumplanetary
dust particles is extremely rich: Physical and dynamical processes
acting on circumplanetary dust are electrical charging, forces
including planetary gravity, radiation forces, electromagnetic forces,
drag forces from interactions with radiation (Poynting-Robertson
effect) and neutral and charged particles, destruction and generation
of grains, interactions with nearby satellites, and resonances - even
collective effects are suggested. The ranking of these dynamic effects
is hotly discussed.
Sometimes the source of a ring
is obvious, in other cases no source has been identified. Models
(sometimes conflicting) have been developed in the past to explain
characteristics of a specific ring. Because of the wealth of new data
on all dusty rings that is becoming available in very recent years it
is time to start a reflection on commonalities and diversities in order
to obtain a deeper understanding of this exciting widespread
astrophysical phenomenon.
It is time to synthesize all
these new observations and to try to develop a unified view of all
dusty rings, especially those in the Jupiter and Saturn system. The
workshop is intended to bring together a team of leading observers and
modelers in order to provide a stimulating environment for new ideas
and amalgamation of diverse views.
Questions to be addressed by
the workshop are:
<!--[if
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<!--[endif]-->What are the
physical properties of distinct regions in the dusty rings?
<!--[if
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<!--[endif]-->What are the most
important dynamic mechanisms determining the shape of the rings?
<!--[if
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<!--[endif]-->What are the
chemical compositions of the different rings?
<!--[if
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<!--[endif]-->What is the mass
flux into the various ring systems?
<!--[if
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<!--[endif]-->What are the
influences of the magnetosphere and plasma environment of the rings?
<!--[if
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<!--[endif]-->What are the
sources of dust grains and what is their production rate?
<!--[if
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<!--[endif]-->What is the
lifetime of dust grains?
<!--[if
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<!--[endif]-->How old are
planetary rings?
<!--[if
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<!--[endif]-->How do dust rings
evolve?
<!--[if
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<!--[endif]-->What causes the
tenuous ring systems to differ so much?
<!--[if
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<!--[endif]-->Why are some faint
rings confined while others are vertically or radially extended?
<!--[if
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<!--[endif]-->Which of the
phenomena displayed by dusty rings are relevant to the collisionally
dominated classical ring systems?
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Michel Blanc | F |
Shawn Brooks | USA |
Joe Burns | USA |
Hiroshi Daisaka | Japan |
Stan Dermott | USA |
Valeri Dikarev | D, RU |
Amara Graps | I |
Eberhard Grün (Team Lead) | D |
Doug Hamilton | USA |
Ove Havnes | N |
Mihaly Horanyi | USA |
Antal Juhasz | HU |
Sascha Kempf | D |
Alexander Krivov | D |
Harald Krüger | D |
Tadashi Mukai | Japan |
Imke de Pater | USA |
Sho Sasaki | Japan |
Mark Showalter | USA |
Frank Spahn | D |
Ralf Srama | D |
Henry Throop | USA |