is the sixth-largest moon
. It was discovered in 1789 by William Herschel
. Until the two Voyager
spacecraft passed near it in the early 1980s, very little was known about this small moon besides the identification of water ice on its surface. The Voyagers showed that Enceladus is only 500 km in diameter and reflects almost 100% of the sunlight
that strikes it. Voyager 1
found that Enceladus orbited in the densest part of Saturn's diffuse E ring
, indicating a possible association between the two, while Voyager 2
revealed that despite the moon's small size, it had a wide range of terrains ranging from old, heavily cratered
surfaces to young, tectonically deformed terrain
, with some regions with surface ages as young as 100 million
years old. The Cassini
spacecraft of the mid- to late 2000s acquired additional data on Enceladus, answering a number of the mysteries opened by the Voyager
spacecraft and starting a few new ones. Cassini
performed several close flybys of Enceladus in 2005, revealing the moon's surface and environment in greater detail. In particular, the probe discovered a water-rich plume venting from the moon's south polar region
. This discovery, along with the presence of escaping internal heat and very few (if any) impact craters in the south polar region, shows that Enceladus is geologically active today. Moons in the extensive satellite systems of gas giants often become trapped in orbital resonances
that lead to forced libration
or orbital eccentricity
; proximity to the planet can then lead to tidal heating
of the satellite's interior, offering a possible explanation for the activity.
Dr. Rosaly M. C. Lopes is a prominent planetary geologist, volcanologist, the author of numerous scientific papers and several books, as well as a great proponent of education. Her major research interests are in planetary and terrestrial surface processes with an emphasis on volcanology.
Lopes was (born January 1957 in Rio de Janeiro, Brazil), where she lived near the famous Ipanema beach. She moved to London, England, in 1975 to study astronomy at the University of London, from where she graduated with honors in astronomy in 1978. For her doctoral studies, she specialized in planetary geology and volcanology and completed her Ph.D. in Planetary Science in 1986 with a thesis on comparing volcanic processes on Earth and Mars. During her Ph.D. she traveled extensively to active volcanoes, particularly Mount Etna in Sicily, and became a member of the UK's Volcanic Eruption Surveillance Team.
She joined JPL as National Research Council Resident Research Associate in 1989 and, after 2 years, became a member of the Galileo Flight project. Lopes worked on the Near Infra-red Mapping Spectrometer (NIMS) team planning and analyzing of observations of Jupiter's volcanic moon Io from 1996 to 2001, during which time she discovered 71 volcanoes on Io that had never before been detected as active. In 2002, Lopes became Investigation Scientist on the Cassini RADAR Team. She has participated on several studies of future NASA and ESA missions as a member of the science definition team, including missions to Saturn and Titan.