Enceladus: Saturn's Remarkable, Watery Moon

John Spencer

Institute Scientist, Southwest Research Institute

Videography by Nerine & Robert Clemenzi, Edited by Nerine Clemenzi
Copyright © Philosophical Society of Washington.  All rights reserved.

John Spencer


Enceladus, an icy moon of Saturn just 300 miles in diameter, is one of the most remarkable worlds in the solar system. Close-up observations by the Saturn-orbiting Cassini spacecraft in 2005 demonstrated that Enceladus is spraying plumes of ice and water vapor thousands of miles into space from four warm trenches near its south pole. This discovery makes Enceladus the only known geologically active ice world. Cassini has continued to explore Enceladus since 2005 with a daring series of close flybys, flying deep into the plume, returning incredibly detailed images of the plumes and the rugged surface of Enceladus, and mapping the heat escaping from its active fractures.

The active plumes not only make Enceladus exceptionally interesting, but they conveniently deliver fresh samples from its interior directly into Cassini's instruments. Onboard analysis of these samples strongly suggests that the plumes erupt from reservoirs of liquid water somewhere beneath the south pole of Enceladus, and that the water might be connected to an underground ocean. This warm, wet, interior, which is rich in complex carbon-based molecules, makes Enceladus one of the most promising known environments for extraterrestrial life. This richly illustrated talk will describe Enceladus' place in the Saturn system, the discovery of activity, what we have learned from Cassini's continued exploration of Enceladus, and the prospects for future missions to this fascinating world.

The Speaker

John Spencer is Institute Scientist at Southwest Research Institute's Department of Space Studies in Boulder, Colorado. He earned a BS in Geology from Cambridge University and a PhD in Planetary Sciences from the University of Arizona. Before joining the Southwest Research Institute he worked at the University of Hawaii, and at the Lowell Observatory in Flagstaff, Arizona. He was a science team member on the Jupiter-orbiting Galileo spacecraft, and is now working on the mapping of temperatures on Saturn's moons using the Composite Infrared Spectrometer (CIRS) on the Cassini Saturn orbiter. He is also a member of the science team on the New Horizons mission which will reach Pluto in 2015. He recently worked on NASA studies of future missions to Enceladus and Jupiter's moon Europa, and led the Outer Planet Satellites panel of NASA's 2009-2011 Planetary Decadal Survey.

John specializes in studies of the large moons of the outer planets, and Pluto, using Earth-based telescopes, close-up spacecraft observations, and the Hubble Space Telescope. He is particularly interested in the geologically active worlds Io (a moon of Jupiter), and Enceladus (a moon of Saturn). His work includes the discovery of several major volcanic eruptions on Io, and the first observations of Io's volcanic eruption plumes with the Hubble Space Telescope, including the discovery of sulfur gas in the plumes. He helped to discover icy volcanic activity on Saturn's moon Enceladus, oxygen in the ice of Jupiter's moon Ganymede, and the probable explanation for the black-and-white appearance of Saturn's moon Iapetus.

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