Passage to a Ringed World - NASA's History Office

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the interaction was described as a transonic flow of plasma (above the local speed of sound). Scientists expect the characteristics of the incident flow to vary substantially depending on the location of Titan with respect to Saturn’s magnetosphere. When Titan is exposed to the solar wind, the interaction may be similar to that of other bodies in the solar system such as Mars, Venus or comets (these bodies have substantial interaction with the solar wind, and, like Titan, have atmospheres but no strong internal magnetic fields). Titan’s Wake. The magnetospheric plasma flowing into and around Titan produces a wake. As with the Galilean satellites at Jupiter, the fast, corotating plasma of Saturn’s magnetosphere smashes into Titan from behind, producing a wake that is dragged out in front of the satellite. The process is similar to one in which a wake is created behind a motor boat speeding through the water. In this analogy, Titan is the motor boat and Saturn’s magnetosphere is the water. Instead of the boat going through the water, the water is rushing past the boat. Titan is moving also, in the same direction as Saturn’s magnetosphere, but slower, so the magnetospheric plasma actually pushes the wake out in front of the satellite. Scientists expect the wake to be a mixture of plasma from Titan and Saturn’s magnetosphere. The wake may be a source of plasma for Saturn’s magnetosphere, producing a torus of nitrogen and other elements abundant in Titan’s atmosphere. Magnetospheric Plasma Titan’s Extended Atmosphere and Ionosphere Titan Bow Shock Wake Exploring Titan is like investigating a fullfledged planet. With a radius of 2575 kilometers, Titan is Saturn’s largest moon — larger than the planets Mercury and Pluto. Titan is the second largest moon in the solar system, surpassed only by Jupiter’s Ganymede. This Voyager image of Titan shows the asymmetry in brightness between the moon’s southern and northern hemispheres. Titan’s natural smoggy haze blocked Voyager’s view of the surface. Titan’s wake and the possible bow shock induced by the interaction of Titan with corotating plasma in Saturn’s vast magnetosphere. THE MYSTERIOUS TITAN 29
30 PASSAGE TO A RINGED WORLD Titan’s Torus. The interaction of Titan with Saturn’s magnetosphere provides a mechanism for both the magnetospheric plasma to enter Titan’s atmosphere and for the atmospheric particles to escape Titan. Voyager results suggested that the interaction produces a torus of neutral particles encircling Saturn, making Titan a potentially important source of plasma to Saturn’s magnetosphere. The characteristics of this torus are yet to be explored and will be addressed by the Cassini Orbiter. The interaction of ice particles and dust from Saturn’s rings will play a special role as the dust moves out toward Titan’s torus and becomes charged by collisions. When the dust is charged, it behaves partially like a neutral particle orbiting Titan, according to Kepler’s laws (gravity driven), and partially like a charged particle moving with Saturn’s The flow of charged particles in Saturn’s magnetosphere past Titan is slowed by the ions created from collisions with Titan’s extended atmosphere. Saturn’s magnetic field becomes draped around Titan. Saturn’s Magnetic Field Incident Flow magnetosphere. The interaction of dust with Saturn’s magnetosphere will provide scientists with a detailed look at how dust and plasma interact. Atmosphere–Magnetosphere Interaction. Saturn’s magnetospheric plasma, which is trapped in the planet’s strong magnetic field, corotates with Saturn, resulting in the plasma flowing into Titan’s back side. The flow picks up ions created by the ionization of neutrals from Titan’s exosphere and is slowed down while the magnetic field wraps around the satellite. The characteristics of the incident flow are important because the incoming plasma is a substantial source of atmospheric ionization that triggers the creation of organic molecules in Titan’s atmosphere. Thus, the aeronomy (study of the physics of atmospheres) of the upper atmosphere and ionosphere is dependent on the Titan’s Extended Atmosphere Titan plasma flow and the solar radiation as a source of energy. Scientists expect that heavy hydrocarbons are the dominant ions in Titan’s ionosphere. Lightning on Titan? The extensive atmosphere of Titan may host Earthlike electrical storms and lightning. Although no evidence of lightning on Titan has been observed, the Cassini–Huygens mission provides the opportunity to determine whether such lightning exists. In addition to the visual search for lightning, the study of plasma waves in the vicinity of Titan may offer another method. Lightning discharges a broad band of electromagnetic emission, part of which can propagate along magnetic field lines as whistler-mode emission. The emissions are known as “whistlers” because, as detected by radio and plasma-wave instruments, they Ionosphere
Page 1: Passage to a Ringed World The Cassi
Page 4 and 5: On the Cover: A collage of images s
Page 6 and 7: FOREWORD This book is for you. You
Page 8 and 9: ACKNOWLEDGMENTS This book would not
Page 10 and 11: Three separate images, taken by Voy
Page 12 and 13: descent to the surface. The Huygens
Page 14 and 15: address the challenges of the missi
Page 16 and 17: Participant Nations* * First flag i
Page 18 and 19: PROBING A MOON OF MYSTERY Huygens
Page 20 and 21: TOUR T18-3 TARGETED SATELLITE FLYBY
Page 22 and 23: SATURN CASSINI-HUYGENS MISSION SCIE
Page 24 and 25: Cassini-Huygens designed to determi
Page 26 and 27: In this diagram from his book, Syst
Page 28 and 29: This Voyager 1 image shows Saturn
Page 30 and 31: An Extended Atmosphere From Liquid
Page 32 and 33: Haze layers are also observed above
Page 34 and 35: IN THE EYE OF THE BEHOLDER Taken fr
Page 36 and 37: This spectacular view of the edge o
Page 40 and 41: have a signature of a tone decreasi
Page 42 and 43: CONSTITUENTS OF THE TITAN ATMOSPHER
Page 44 and 45: The processes of plate tectonics an
Page 46 and 47: tan was accreting, it is possible t
Page 48 and 49: Surface Science. The highest resolu
Page 50 and 51: This enhanced Voyager 2 image shows
Page 52 and 53: Voyager 1 captured this striking im
Page 54 and 55: Prometheus and Pandora, two tiny sa
Page 56 and 57: In the stellar occultation experime
Page 58 and 59: scattering than are larger particle
Page 60 and 61: In fact, Saturn’s rings — as we
Page 62 and 63: The satellites of Saturn comprise a
Page 64 and 65: Before the advent of spacecraft exp
Page 66 and 67: The bright surface of Saturn’s mo
Page 68 and 69: Galilean satellites. Most of what i
Page 70 and 71: duced that one hemisphere is compos
Page 72 and 73: patches on the surface. Although it
Page 74 and 75: Artist’s conception of Ithaca Cha
Page 76 and 77: An artist’s rendition of Saturn
Page 78 and 79: The MAPS Instruments Coordinated ob
Page 80 and 81: field reverses direction across the
Page 82 and 83: SATURN’S MAGNETIC FIELD Saturn’
Page 84 and 85: Solar Wind Magnetosheath Titan neut
Page 86 and 87: per atmosphere. Energetic particles
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and plasma wave emissions from narr
Page 90 and 91:
CHAPTER 7 Space mission design aims
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(SOI) propulsive maneuver to initia
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the tour cannot continue. Of course
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crease inclination to this value. T
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This illustration shows the main de
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discussed earlier) and data handlin
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of the spacecraft! Below the oxidiz
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• Opening or shutting thermal lou
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management subsystem and the Probe
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falls below its storage temperature
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The Cassini-Huygens spacecraft stan
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The Imaging Science Subsystem (ISS)
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• Map the composition and thermal
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cise distance between the surface f
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• Study the interaction of the ma
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• Study the erosional and electro
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midway out on the magnetometer boom
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The RPWS instrument will be used to
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altitudes down to 40 kilometers abo
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dex. A group of platinum resistance
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CHAPTER 10 Mission operations are t
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PLANETARY MISSION OPERATIONS Functi
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two low-gain antennas 1 and will pr
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During much of Cassini’s orbital
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articulation control subsystem’s
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AFTERWORD It has been said that in
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Developments tied to the Cassini-Hu
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APPENDIX A Command. A data transact
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APPENDIX A 138 PASSAGE TO A RINGED
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APPENDIX A Plasma wave. A wave char
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APPENDIX A 142 PASSAGE TO A RINGED
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APPENDIX B H O 2 + Water molecule w
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APPENDIX C 146 PASSAGE TO A RINGED
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APPENDIX D 148 PASSAGE TO A RINGED
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APPENDIX D 150 PASSAGE TO A RINGED
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APPENDIX F 152 PASSAGE TO A RINGED
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APPENDIX F 154 PASSAGE TO A RINGED
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APPENDIX F Peralta, F. and S. Flana
Page 168:
National Aeronautics and Space Admi
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