News and commentary about the Great Frontiers

ISS007-E-10807 (21 July 2003) --- This view of Earth's horizon as the sunsets over the Pacific Ocean was taken by an Expedition 7 crewmember onboard the International Space Station (ISS). Anvil tops of thunderclouds are also visible. Credit: Earth Science and Remote Sensing Unit, NASA Johnson Space Center

Image Credit: ISS007-E-10807 (21 July 2003) – Earth Science and Remote Sensing Unit, NASA Johnson Space Center

Potential Liquid Water on Enceladus



Cassini-Huygens mission scientists discovered last year that plumes of ice erupt from the surface of Saturn’s moon Enceladus, but the mechanism for the this process has not been fully explained. Now a review of competing theories and available data implicates the more unlikely source: pressurized liquid water pools or an ocean near the moon’s surface. How water can be liquid on an apparently frozen body in the cold of the distant solar system is just the latest mystery regarding Enceladus.

Several research papers regarding recent findings about Enceladus are available in the March 10, 2006 issue of Science. In a Research Article entitled “Cassini Observes the Active South Pole of Enceladus”, Dr. Carolyn Porco, Cassini imaging team leader at Space Science Institute in Boulder, Colorado, USA and other mission scientists suggest that “water vapor probably venting from subsurface reservoirs of liquid water” provides the source for the majestic surface plumes discovered last year. In turn, these plumes may continually replenish Saturn’s E-ring.

Enceladus become just the fourth object in the solar system suspected of containing liquid water reservoirs because of tantalizing new evidence. Only Earth is known for certain to have liquid water on and below its surface. Evidence for liquid water aquifers on Mars and an ocean deep beneath the ice on Jupiter’s moon Europa have already led to excitement within the scientific community over the past decade. Now that Enceladus has been added to list, the mystery of processes that lead to liquid water only deepens.

If pools or oceans of liquid water exist on Enceladus, where do they come from? A heating source is required to raise the temperature to above 273 degrees Kelvin (0 degrees Celsius.) Mission scientists suspect flexing of the moon caused by its orbit around Saturn or a gravitational tug-of-war between Titan and Saturn, along with radioactive decay within the moon’s interior lead to heating that locally heats crustal water ice. Under pressure, this liquid water eventually escapes to the surface as geysers near the moon’s south pole.

The region near Enceladus’ south pole is striking for its so-called Tiger Stripes, enormous gashes across the surface that a significantly more warm than the surrounding terrain. The lack of craters and the apparent youth of ice in the area all suggest recent resurfacing. The discovery of the ice plumes confirmed this observation.

Mission scientists will continue to sift through the data returned by Cassini to investigate Enceladus. Cassini is currently scheduled to return for a close flyby of Enceladus on Wednesday, March 12, 2008 after a mission focus on Titan over the next two years has concluded.

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