Iapetus Robert Cai Fall 2014 Introduc8on • Also known as Japetus • Is third largest moon of Saturn • In total, Saturn has at least 150 moons and moonlets • Titan is the largest moon of Saturn, and Rhea is the second largest • Is eleventh largest moon in Solar System • Has a dramac two-tone coloraon • Was photographed by Cassini spaceprobe in 2007 • Has a large equatorial ridge Photomosaic of Iapetus images taken by Cassini spaceprobe Reference: hNp://en.wikipedia.org/wiki/Iapetus_%28moon%29 hNp://en.wikipedia.org/wiki/Saturn Discovery - Giovanni Domenico Cassini - Biography • Lived from June 8, 1625 unl September 14, 1712 • Was born in Perinaldo, Republic of Genova • Died in Paris, France, at the age of 87 • Was an Italian astronomer, as well as a mathemacian, engineer, and astrologer • Was the principal chair of Pain8ng of Giovanni Domenico astronomy at the University of Cassini, discoverer of Iapetus Bologna Reference: hNp://en.wikipedia.org/wiki/Giovanni_Domenico_Cassini Discovery - Giovanni Domenico Cassini - Relevance • Discovered Iapetus on October 25, 1671 • Also discovered three other moons of Saturn • Observed the division of the rings of Saturn, later named the Cassini Division • The Cassini spaceprobe was named aer him Pain8ng of Giovanni Domenico Cassini, discoverer of Iapetus Reference: hNp://en.wikipedia.org/wiki/Giovanni_Domenico_Cassini Origin of Name • The moon Iapetus is named aer the Titan Iapetus, God of Mortality, from Greek mythology • The Titan Iapetus was: • The son of the God Uranus and Goddess Gaia • The father of the Titans Atlas, Prometheus, Epimetheus, and Menoe8us • The brother of the Titan Bust of Iapetus, a Titan from Greek mythology Cronus • The moon Iapetus’ alternave name is Saturn VIII Reference: hNp://en.wikipedia.org/wiki/Iapetus_%28mythology%29 Orbital Characteris8cs • Semi-major axis (longest diameter of Iapetus’ orbit): 3,560,820 km • Eccentricity (amount of deviaon of Iapetus’ orbit from a perfect circle): 0.0286125 • Orbital period (amount of 8me for one complete Iapetus orbit): 79.3215 days • Average orbital speed (average speed of Iapetus’ orbit): 3.26 km/s • Inclinaon (angle of Iapetus’ orbital plane with respect to a reference plane): 17.28° (to the eclip8c); 15.47° (to Saturn’s equator), 8.13° (to Laplace plane) • Satellite of: Saturn Reference: hNp://en.wikipedia.org/wiki/Iapetus_%28moon%29 Physical Characteris8cs - Stats • Dimensions: 1,492.0 x 1,492.0 x 1,424 km • Mean radius: 734.5 + 2.8 km • Surface area: 6,700,000 km2 • Mass: (1.805635 + 0.000375) x 1021 kg • Mean density: 1.088 + 0.013 g/cm3 • Surface gravity (gravitaonal acceleraon at Iapetus’ surface): 0.224 m/s2 • Escape velocity (speed needed to overcome Iapetus’ gravitaonal arac8on): 0.573 km/s • Rota;on period (amount of 8me for one complete revolu8on of Iapetus around its rotaonal axis): 79.3215 days • Axial ;lt (angle between Iapetus’ rotaonal axis and orbital axis): zero • Albedo (reflecng power of Iapetus’ surface): 0.05 – 0.5 • Temperature: 90 – 130 K • Apparent magnitude: 10.2 – 11.9 Reference: hNp://en.wikipedia.org/wiki/Iapetus_%28moon%29 Physical Characteris8cs - Descrip8ons • Two-tone coloraon – Cassini Regio: dark region of Iapetus – Roncevaux Terra, Saragossa Terra: bright regions of Iapetus • Shape – O\en characterized as walnut- shaped – Contains bulging equatorial area due to ridge • Equatorial ridge – About 1,300 km long, 20 km wide, and 13 km high Mosaic of Iapetus taken by Cassini – Located along the center of spaceprobe Cassini Regio Reference: hNp://en.wikipedia.org/wiki/Iapetus_%28moon%29 Physical Characteris8cs – Equatorial Ridge • Two theories regarding the origin of the equatorial ridge: – The ridge may have formed at an earlier me when Iapetus rotated much faster than it currently does Photo showing close view of equatorial – The ridge may have ridge formed out of material le\ from the collapse of a ring at an earlier me Reference: hNp://solarsystem.nasa.gov/planets/profile.cfm?Object=Iapetus Orbit • Overall, Iapetus has an unusually distant and inclined orbit Side view of Iapetus’ Polar view of Iapetus’ orbit shows unusually orbit shows unusually high inclinaon high distance from Saturn Reference: hNp://en.wikipedia.org/wiki/Iapetus_%28moon%29 Exploraon – Cassini spaceprobe • Launched on October 15, 1997 aer about two decades of development • Entered orbit around Saturn on July 1, 2004 • Has imaged Iapetus mulple Digital image of Cassini spaceprobe 8mes from moderate distances • Has imaged Iapetus once from close distance on September 10, 2007 Reference: hNp://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens Bibliography • hNp://en.wikipedia.org/wiki/Iapetus_ %28moon%29 • hNp://en.wikipedia.org/wiki/ Giovanni_Domenico_Cassini • hNp://en.wikipedia.org/wiki/Iapetus_ %28mythology%29 • hNp://en.wikipedia.org/wiki/Cassini %E2%80%93Huygens .