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Subject: FW: Cassini Spacecraft Reveals 101 Geysers and more on Icy Saturn Moon
From:
Subject: FW: Cassini Spacecraft Reveals 101 Geysers and more on Icy Saturn Moon
Date: Tue, 29 Jul 2014 15:55:38 -0500
July 28, 2014
RELEASE 14-203
Cassini Spacecraft Reveals 101 Geysers and more on Icy Saturn Moon
Scientists using mission data from NASA's Cassini spacecraft have identified 101 distinct geysers erupting on Saturn's icy moon Enceladus. Their analysis suggests it is possible for liquid water to reach from the moon's underground sea all the way to its surface.
This artist's rendering shows a cross-section of the ice shell immediately beneath one of Enceladus' geyser-active fractures, illustrating the physical and thermal structure and the processes ongoing below and at the surface.
Image Credit: NASA/JPL-Caltech/Space Science Institute
These findings, and clues to what powers the geyser eruptions, are presented in two articles published in the current online edition of the Astronomical Journal.
Over a period of almost seven years, Cassini's cameras surveyed the south polar terrain of the small moon, a unique geological basin renowned for its four prominent "tiger stripe" fractures and the geysers of tiny icy particles and water vapor first sighted there nearly 10 years ago. The result of the survey is a map of 101 geysers, each erupting from one of the tiger stripe fractures, and the discovery that individual geysers are coincident with small hot spots. These relationships pointed the way to the geysers' origin.
After the first sighting of the geysers in 2005, scientists suspected repeated flexing of Enceladus by Saturn's tides as the moon orbits the planet had something to do with their behavior. One suggestion included the back-and-forth rubbing of opposing walls of the fractures generating frictional heat that turned ice into geyser-forming vapor and liquid.
Alternate views held that the opening and closing of the fractures allowed water vapor from below to reach the surface. Before this new study, it was not clear which process was the dominating influence. Nor was it certain whether excess heat emitted by Enceladus was everywhere correlated with geyser activity.
To determine the surface locations of the geysers, researchers employed the same process of triangulation used historically to survey geological features on Earth, such as mountains. When the researchers compared the geysers' locations with low-resolution maps of thermal emission, it became apparent the greatest geyser activity coincided with the greatest thermal radiation. Comparisons between the geysers and tidal stresses revealed similar connections. However, these correlations alone were insufficient to answer the question, "What produces what?"
The answer to this mystery came from comparison of the survey results with high-resolution data collected in 2010 by Cassini's heat-sensing instruments. Individual geysers were found to coincide with small-scale hot spots, only a few dozen feet (or tens of meters) across, which were too small to be produced by frictional heating, but the right size to be the result of condensation of vapor on the near-surface walls of the fractures. This immediately implicated the hot spots as the signature of the geysering process.
"Once we had these results in hand we knew right away heat was not causing the geysers, but vice versa," said Carolyn Porco, leader of the Cassini imaging team from the Space Science Institute in Boulder, Colorado, and lead author of the first paper. "It also told us the geysers are not a near-surface phenomenon, but have much deeper roots."
Thanks to recent analysis of Cassini gravity data, the researchers concluded the only plausible source of the material forming the geysers is the sea now known to exist beneath the ice shell. They also found that narrow pathways through the ice shell can remain open from the sea all the way to the surface, if filled with liquid water.
In the companion paper, the authors report the brightness of the plume formed by all the geysers, as seen with Cassini's high resolution cameras, changes periodically as Enceladus orbits Saturn. Armed with the conclusion the opening and closing of the fractures modulates the venting, the authors compared the observations with the expected venting schedule due to tides.
They found the simplest model of tidal flexing provides a good match for the brightness variations Cassini observes, but it does not predict the time when the plume begins to brighten. Some other important effect is present and the authors considered several in the course of their work.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory (JPL) in Pasadena, California, manages the mission for NASA's Science Mission Directorate in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team consists of scientists from the United States, England, France and Germany. The imaging team is based at the Space Science Institute.
Additional details, images and an animation are available at:
http://www.ciclops.org/view_event/202
More information about Cassini is available at:
http://www.nasa.gov/cassini
and
http://saturn.jpl.nasa.gov
-end-
Dwayne Brown
Headquarters, Washington
202-358-1726
dwayne.c.brown@nasa.gov
Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013
preston.dyches@jpl.nasa.gov
Steve Mullins
Space Science Institute, Boulder, Colo.
720-974-5859
media@ciclops.org
101 Geysers Mapped on Ocean-Bearing Saturn Moon Enceladus
By Mike Wall, Senior Writer | July 29, 2014 07:17am ET
The icy Saturn moon Enceladus sports at least 101 geysers, which reach all the way down to the satellite's subsurface ocean, new research suggests.
A view from NASA's Cassini spacecraft looking across the geyser basin near the south pole of Saturn's moon Enceladus, along fractures spewing water vapor and ice particles into space.
Credit: NASA/JPL-Caltech/SSI View full size image
Scientists mapped out 101 geysers of water vapor and ice near Enceladus' south pole after analyzing images captured by NASA's Cassini spacecraft over a period of nearly seven years. This effort also helped astronomers trace the eruptions to their source, researchers said.
Cassini first spotted geysers erupting from four "tiger stripe" fractures on Enceladus — a 310-mile-wide (500 kilometers) moon covered by an icy shell — in 2005, but their origin remains the subject of some debate to this day. [Photos: Enceladus, Saturn's Cold, Bright Moon]For example, some scientists think the geysers are driven by frictional heat generated when the tiger stripes' walls rub together. This scenario implies that the plumes consist of material from Enceladus' surface, or just beneath it.
Graphic showing a 3D model of 98 geysers spotted by a Cassini imaging survey of Enceladus' south polar region
Credit: ASA/JPL-Caltech/Space Science InstituteView full size image
But other researchers posit that the geysers reach all the way down to the ocean of liquid water that sloshes beneath Enceladus' icy shell, and that they blast into space when the fractures open up. If this is the case, future spacecraft that collect material from the plumes could sample this ocean without even touching down on the moon — a prospect that excites astrobiologists, who view Enceladus as one of the solar system's best bets to host alien life.
Researchers compared the locations of the newly mapped 101 geysers with precision data gathered in 2010 by Cassini's heat-sensing gear. They determined that each eruption is associated with a hot spot measuring just a few dozen feet across — too small to be generated by fracture walls rubbing together.
"Once we had these results in hand, we knew right away heat was not causing the geysers, but vice versa," lead author Carolyn Porco, leader of the Cassini imaging team from the Space Science Institute in Boulder, Colorado, said in a statement. "It also told us the geysers are not a near-surface phenomenon, but have much deeper roots."
Those roots reach the moon's subsurface sea via unfrozen conduits in Enceladus' ice shell, the team concluded.In a second study, astronomers found that Enceladus' overall geyser-generated plume varies in brightness as the moon makes its way around Saturn. They determined that tidal heating — which is generated when the gravity of Saturn and the nearby moon Dione tug on Enceladus — is probably the main cause of the brightness variations, though some other unknown factors appear to be playing a role as well.
Artist's concept showing a cross-section of the ice shell beneath one of Enceladus' "tiger stripe" fractures, from which geysers of water vapor and ice blast into space.
Credit: NASA/JPL-Caltech/Space Science InstituteView full size image
Both new studies appear in the latest issue of the Astronomical Journal.
The $3.2 billion Cassini mission — a joint effort of NASA, the European Space Agency and the Italian Space Agency — launch in 1997 and arrived in orbit around Saturn in 2004. The spacecraft is scheduled to keep studying the ringed planet and its many moons until September 2017, when it will perform an intentional death dive into the gas giant's atmosphere.
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