Magnetospheric and Plasma Science with Cassini-Huygens |
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Authors: | Blanc M Bolton S Bradley J Burton M Cravens TE Dandouras I Dougherty MK Festou MC Feynman J Johnson RE Gombosi TG Kurth WS Liewer PC Mauk BH Maurice S Mitchell D Neubauer FM Richardson JD Shemansky DE Sittler EC Tsurutani BT Zarka Ph Esposito LW Grün E Gurnett DA Kliore AJ Krimigis SM Southwood D Waite JH Young DT |
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Institution: | 1.Observatoire Midi-Pyrénées, Toulouse, France ;2.Jet Propulsion Laboratory, Pasadena, California ;3.University of Kansas, Lawrence, Kansas ;4.CESR, Toulouse, France ;5.The Blackett Laboratory, Imperial College, London, U.K ;6.University of Virginia, Charlottesville, Virginia ;7.Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan ;8.Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa ;9.Applied Physics Laboratory, The Johns Hopkins University, Laurel, Maryland ;10.Institute for Geophysics and Meteorology, K?ln University, K?ln, Germany ;11.Center for Space Research, MIT, Cambridge, Massachusetts ;12.Department of Aerospace Engineering, University of Southern California, Los Angeles, California ;13.Goddard Space Flight Center, Greenbelt, Maryland ;14.DESPA, Observatoire de Paris-Meudon, Meudon, France ;15.Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado ;16.Max-Planck-Institut für Kernphysik, Heidelberg, Germany ;17.Southwest Research Institute, San Antonio, Texas ; |
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Abstract: | Magnetospheric and plasma science studies at Saturn offer a unique opportunity to explore in-depth two types of magnetospheres.
These are an ‘induced’ magnetosphere generated by the interaction of Titan with the surrounding plasma flow and Saturn's ‘intrinsic’
magnetosphere, the magnetic cavity Saturn's planetary magnetic field creates inside the solar wind flow. These two objects
will be explored using the most advanced and diverse package of instruments for the analysis of plasmas, energetic particles
and fields ever flown to a planet. These instruments will make it possible to address and solve a series of key scientific
questions concerning the interaction of these two magnetospheres with their environment.
The flow of magnetospheric plasma around the obstacle, caused by Titan's atmosphere/ionosphere, produces an elongated cavity
and wake, which we call an ‘induced magnetosphere’. The Mach number characteristics of this interaction make it unique in
the solar system. We first describe Titan's ionosphere, which is the obstacle to the external plasma flow. We then study Titan's
induced magnetosphere, its structure, dynamics and variability, and discuss the possible existence of a small intrinsic magnetic
field of Titan.
Saturn's magnetosphere, which is dynamically and chemically coupled to all other components of Saturn's environment in addition
to Titan, is then described. We start with a summary of the morphology of magnetospheric plasma and fields. Then we discuss
what we know of the magnetospheric interactions in each region. Beginning with the innermost regions and moving outwards,
we first describe the region of the main rings and their connection to the low-latitude ionosphere. Next the icy satellites,
which develop specific magnetospheric interactions, are imbedded in a relatively dense neutral gas cloud which also overlaps
the spatial extent of the diffuse E ring. This region constitutes a very interesting case of direct and mutual coupling between
dust, neutral gas and plasma populations. Beyond about twelve Saturn radii is the outer magnetosphere, where the dynamics
is dominated by its coupling with the solar wind and a large hydrogen torus. It is a region of intense coupling between the
magnetosphere and Saturn's upper atmosphere, and the source of Saturn's auroral emissions, including the kilometric radiation.
For each of these regions we identify the key scientific questions and propose an investigation strategy to address them.
Finally, we show how the unique characteristics of the CASSINI spacecraft, instruments and mission profile make it possible
to address, and hopefully solve, many of these questions. While the CASSINI orbital tour gives access to most, if not all,
of the regions that need to be explored, the unique capabilities of the MAPS instrument suite make it possible to define an
efficient strategy in which in situ measurements and remote sensing observations complement each other.
Saturn's magnetosphere will be extensively studied from the microphysical to the global scale over the four years of the mission.
All phases present in this unique environment — extended solid surfaces, dust and gas clouds, plasma and energetic particles
— are coupled in an intricate way, very much as they are in planetary formation environments. This is one of the most interesting
aspects of Magnetospheric and Plasma Science studies at Saturn. It provides us with a unique opportunity to conduct an in situ investigation of a dynamical system that is in some ways analogous to the dusty plasma environments in which planetary systems
form.
This revised version was published online in August 2006 with corrections to the Cover Date. |
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