Cassini Finds Global Ocean in Saturn's Moon Enceladus
Illustration of the interior of Saturn's moon Enceladus showing a global liquid water ocean between its rocky core and icy crust. Thickness of layers shown here is not to scale.
Credits: NASA/JPL-Caltech
A global ocean lies beneath the icy crust of Saturn's geologically active moon Enceladus, according to new research using data from NASA's Cassini mission.
Researchers found the magnitude of the moon's very slight wobble, as it orbits Saturn, can only be accounted for if its outer ice shell is not frozen solid to its interior, meaning a global ocean must be present.
The finding implies the fine spray of water vapor, icy particles and simple organic molecules Cassini has observed coming from fractures near the moon's south pole is being fed by this vast liquid water reservoir. The research is presented in a paper published online this week in the journal Icarus.
Previous analysis of Cassini data suggested the presence of a lens-shaped body of water, or sea, underlying the moon's south polar region. However, gravity data collected during the spacecraft's several close passes over the south polar region lent support to the possibility the sea might be global. The new results -- derived using an independent line of evidence based on Cassini's images -- confirm this to be the case.
"This was a hard problem that required years of observations, and calculations involving a diverse collection of disciplines, but we are confident we finally got it right," said Peter Thomas, a Cassini imaging team member at Cornell University, Ithaca, New York, and lead author of the paper.
Cassini scientists analyzed more than seven years' worth of images of Enceladus taken by the spacecraft, which has been orbiting Saturn since mid-2004. They carefully mapped the positions of features on Enceladus -- mostly craters -- across hundreds of images, in order to measure changes in the moon's rotation with extreme precision.
As a result, they found Enceladus has a tiny, but measurable wobble as it orbits Saturn. Because the icy moon is not perfectly spherical -- and because it goes slightly faster and slower during different portions of its orbit around Saturn -- the giant planet subtly rocks Enceladus back and forth as it rotates.
The team plugged their measurement of the wobble, called a libration, into different models for how Enceladus might be arranged on the inside, including ones in which the moon was frozen from surface to core.
"If the surface and core were rigidly connected, the core would provide so much dead weight the wobble would be far smaller than we observe it to be," said Matthew Tiscareno, a Cassini participating scientist at the SETI Institute, Mountain View, California, and a co-author of the paper. "This proves that there must be a global layer of liquid separating the surface from the core," he said.
The mechanisms that might have prevented Enceladus' ocean from freezing remain a mystery. Thomas and his colleagues suggest a few ideas for future study that might help resolve the question, including the surprising possibility that tidal forces due to Saturn's gravity could be generating much more heat within Enceladus than previously thought.
"This is a major step beyond what we understood about this moon before, and it demonstrates the kind of deep-dive discoveries we can make with long-lived orbiter missions to other planets," said co-author Carolyn Porco, Cassini imaging team lead at Space Science Institute (SSI), Boulder, Colorado, and visiting scholar at the University of California, Berkeley. "Cassini has been exemplary in this regard."
The unfolding story of Enceladus has been one of the great triumphs of Cassini's long mission at Saturn. Scientists first detected signs of the moon's icy plume in early 2005, and followed up with a series of discoveries about the material gushing from warm fractures near its south pole. They announced strong evidence for a regional sea in 2014, and more recently, in 2015, they shared results that suggest hydrothermal activity is taking place on the ocean floor.
Cassini is scheduled to make a close flyby of Enceladus on Oct. 28, in the mission's deepest-ever dive through the moon's active plume of icy material. The spacecraft will pass a mere 30 miles (49 kilometers) above the moon's surface.
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, manages the mission for the agency's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena, California. The Cassini imaging operations center is based at Space Science Institute.
For more information about Cassini, visit:
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Dwayne Brown / Laurie Cantillo
Headquarters, Washington
202-358-1726 / 202-358-1077
dwayne.c.brown@nasa.gov / laura.l.cantillo@nasa.gov
Headquarters, Washington
202-358-1726 / 202-358-1077
dwayne.c.brown@nasa.gov / laura.l.cantillo@nasa.gov
Last Updated: Sep. 15, 2015
Editor: Allard Beutel
el dispensador anota en tu margen ► En la mitología griega, Encélado (en griego Ἐγκέλαδος, Enkelados; en latín Enceladus) era uno de los Gigantes de cien brazos, hijo deUrano: brotó de su sangre cuando fue castrado por Crono. Otra versión afirma que nació de la Tierra, que lo engendró por sí misma o con el Tártaro, airada contra los dioses.
Fue derrotado en la guerra con los dioses del Olimpo por los rayos de Zeus y enterrado bajo el monte Etna por Atenea. Sin embargoEurípides afirma que fue Sileno quien le mató con su lanza (si bien podría tratarse de una más de sus bravuconadas), y Pausanias que fue aplastado por Atenea cuando la diosa le lanzó la isla de Sicilia. Las llamas del Etna se suponía que eran la respiración de Encélado, y sus erupciones se producían al restregar su lado herido en el interior del volcán como escribe el poeta Lucilo.
Algunos creen que Encélado es el mismo que Tifón.
- Un hijo de Egipto y Argifia que fue asesinado por su esposa, la danaide Amimone su misma noche de bodas.
el dispensador dice:
a medida que viajes,
la vida te envolverá,
y te sorprenderá,
hasta hacerte comprender,
que nada,
absolutamente nada,
depende de la humanidad...
y entonces llorarás,
de impotencia sentimental,
porque del universo latente,
nada te pertenece,
y nada te pertenecerá,
salvo tu soberbia,
tu miseria humana,
y tu necedad...
pero esto,
pequeño Adam´s,
recién acaba de comenzar...
SEPTIEMBRE 16, 2015.-
A view of Saturn's moon Dione captured by NASA's Cassini spacecraft during a close flyby on June 16, 2015. The diagonal line near upper left is the rings of Saturn, in the distance.
Credits: NASA/JPL-Caltech/Space Science Institute
NASA's Cassini spacecraft will zip past Saturn's moon Dione on Monday, Aug. 17 -- the final close flyby of this icy satellite during the spacecraft's long mission.
Cassini’s closest approach, within 295 miles (474 kilometers) of Dione's surface, will occur at 11:33 a.m. PDT (2:33 p.m. EDT). Mission controllers expect fresh images to begin arriving on Earth within a couple of days following the encounter.
Cassini scientists have a bevy of investigations planned for Dione. Gravity-science data from the flyby will improve scientists' knowledge of the moon's internal structure and allow comparisons to Saturn's other moons. Cassini has performed this sort of gravity science investigation with only a handful of Saturn's 62 known moons.
During the flyby, Cassini's cameras and spectrometers will get a high-resolution peek at Dione's north pole at a resolution of only a few feet (or meters). In addition, Cassini's Composite Infrared Spectrometer instrument will map areas on the icy moon that have unusual thermal anomalies -- those regions are especially good at trapping heat. Meanwhile, the mission's Cosmic Dust Analyzer continues its search for dust particles emitted from Dione.
This flyby will be the fifth targeted encounter with Dione of Cassini's tour at Saturn. Targeted encounters require maneuvers to precisely steer the spacecraft toward a desired path above a moon. The spacecraft executed a 12-second burn using its thrusters on Aug. 9, which fine-tuned the trajectory to enable the upcoming encounter.
Cassini’s closest-ever flyby of Dione was in Dec. 2011, at a distance of 60 miles (100 kilometers). Those previous close Cassini flybys yielded high-resolution views of the bright, wispy terrain on Dione first seen during the Voyager mission. Cassini's sharp views revealed the bright features to be a system of braided canyons with bright walls. Scientists also have been eager to find out if Dione has geologic activity, like Saturn's geyser-spouting moon Enceladus, but at a much lower level.
"Dione has been an enigma, giving hints of active geologic processes, including a transient atmosphere and evidence of ice volcanoes. But we've never found the smoking gun. The fifth flyby of Dione will be our last chance," said Bonnie Buratti, a Cassini science team member at NASA's Jet Propulsion Laboratory in Pasadena, California.
Cassini has been orbiting Saturn since 2004. After a series of close moon flybys in late 2015, the spacecraft will depart Saturn's equatorial plane -- where moon flybys occur most frequently -- to begin a year-long setup of the mission's daring final year. For its grand finale, Cassini will repeatedly dive through the space between Saturn and its rings.
"This will be our last chance to see Dione up close for many years to come," said Scott Edgington, Cassini mission deputy project scientist at JPL. "Cassini has provided insights into this icy moon's mysteries, along with a rich data set and a host of new questions for scientists to ponder."
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL, a division of the California Institute of Technology, manages the mission for NASA's Science Mission Directorate in Washington.
For more information about Cassini, visit:
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