The Cassini-Huygens Mission Orbiter Remote Sensing Investigations

Atthiswriting the Cassini spacecraft has ?redits engine and successfully inserted itself andits precious cargoof scienti'c instruments into orbit, the ?rst step of its exploration of the Saturnian system. The suspense is not over, however. While excitingimages of therings have been captured, anexotic composition of Phoebe sensedby themapping spectrometer and unexpectedpanoply of magneticwaves andplasma dynamics encountered on the incoming trajectory andinitial orbit, the Huygensprobeisstillonboardandthe'rstclose'ybyofTitanhasnottakenplace. Not until Christmas Day will the probe bereleased.Navigators are still checking theircalculations, worryingaboutknownunknownslikethemassofSaturn'smoons that could cause ever so small a deviation from the planned trajectory of the probe. Theorbiter investigators are also anxious but theyget their taste of Titan earlier, on October 26.Howwell will theydetect the surface? How thickisthe atmosphere? Does Titan haveamagnetic'eld?Isthere lightninginthe atmosphere of Titan? While terrestrial and HubbleSpace Telescope pictures have improvedgreatly over the years, they cannot match the resolution obtainable from orbitabout theplanet, and much of the data issimply unobtainablewithout direct insitu sensing. Volume 1 of this three volume set described the Cassini/Huygens mission, its scienti'c objectives and the Huygens probethat will soon enter theTitan at- sphere. Volume 2 described the insitu investigations on theorbiter. In this, the third and ?nal volume of the compendium, we describethe remote sensing inv- tigations: radioscience, radar, visibleandinfrared spectroscopy, thermalinfrared studies, ultraviolet spectroscopy and visible imagery.