50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 2654.pdf CASSINI OBSERVATIONS OF SATURN'S IRREGULAR MOONS. T. Denk1 and S. Mottola2, 1Freie Univer- sität Berlin, Malteserstr. 74-100, 12249 Berlin, Germany (
[email protected]), 2Deutsches Zentrum für Luft- und Raumfahrt (DLR), Rutherfordstr. 2, 12489 Berlin, Germany (
[email protected]). Introduction: Saturn's outer or irregular moons Since Cassini was located inside the orbits of the represent a distinct class of objects in the Solar Sys- irregular moons, but the illumination source (the Sun) tem. They were discovered between 2000 and 2007 was far away (outside the orbits), the phase angles except for Phoebe which has been photographed since could take all values between 0° and 180° (see Table 1 1898. The distances between Saturn and the 38 known for ranges of actual observation phases). This unique objects vary between 7.6 Gm (126 RS; Kiviuq periap- advantage of Cassini would be given to any spacecraft sis) and 33.2 Gm (550 RS; Surtur apoapsis). The irreg- orbiting a giant planet while observing outer moons. ulars are found on orbits of large eccentricity and high The total number of ISS images targeting irregular inclination, both prograde and retrograde. moons is ~38,000, obtained during ~200 observations. Large moon Phoebe has a retrograde orbit and ac- Our Cassini campaign represents the first utilization of counts for more than 98% of the total mass of Saturn's an interplanetary spacecraft for a systematic photomet- irregulars. Of the remaining mass, ~92% belongs to ric survey of irregular moons in the Solar System.