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Module 4 - Follow the Water

Global Ocean on Enceladus

September 15, 2015 - Global Ocean on Enceladus (Artist's Rendering) http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA19656 http://www.jpl.nasa.gov/news/news.php?feature=4718 This illustration based on data from NASA's Cassini spacecraft is of the interior of Saturn's moon Enceladus showing a global liquid water ocean between its rocky core and icy crust. Click here for larger version of PIA19656 => http://photojournal.jpl.nasa.gov/catalog/PIA19058 Annotated Image - Click on the image for larger version => http://photojournal.jpl.nasa.gov/figures/PIA19656_fig1.jpg This illustration is a speculative representation of the interior of Saturn's moon Enceladus with a global liquid water ocean between its rocky core and icy crust. The thickness of layers shown here is not to scale. Scientists on NASA's Cassini mission determined that the slight wobble of Enceladus as it orbits Saturn is much too large for the moon to be frozen from surface to core. The wobble, technically referred to as a libration, reveals that the crust of Enceladus is disconnected from its rocky interior. This graphic is an update to PIA19058, which showed only a regional sea beneath the south polar region of Enceladus. Enceladus is 313 miles (504 kilometers) across. The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini.

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Icy Geysers on Enceladus The volcanoes that Voyager discovered on Io in 1977 erupt hot material. But in 2005, the Cassini orbiter discovered multiple geysers erupting from Saturn’s moon Enceladus. These plumes were seen erupting from regions near the south pole, so you should stand on your head to view the image on the top of the page properly. During multiple fly-bys through the subsequent 10 years the data collected by Cassini have provided significant insights into the composition and activity of this satellite. The closest flyby on October 2015 brought the Cassini orbiter to within 48 km of the south polar region of Enceladus. The results of that flyby had not been published at the time that this course was prepared, but here is what we know about Enceladus so far:

The eruptions above Enceladus are not coming from single point-source vents like volcanoes. Instead the material appears to be erupting from long fractures within the icy shell. The video below shows the real and enhanced versions of these curtains of erupting water. If you want to download large images of this data, go here.

The material that is erupting is not pure water. While it is mostly water, the geysers also contain minor amounts of molecular nitrogen, methane, and carbon dioxide. In addition to methane, Cassini also discovered trace amounts of simple hydrocarbons such as propane, acetylene and formaldehyde. This implies that Enceladus has an internal, salty, liquid ocean.

On September 15, 2015, Carolyn Porco, the Cassini Imaging Team Leader, made a significant announcement in the “Captain’s Logs”. Yes, there really is one - and please note that CICLOPS stands for Cassini Imaging Central Laboratory for Operations.

But back to the announcement. It stated that the liquid ocean within Enceladus is global, extends around the entire satellite. This is significant because there had been debate about the extent of watery layer beneath the icy shell. Now we know that Enceladus does not just have isolated reservoirs of water, but that a complete water layer exists. For an explanation of how the scientists of the Cassini team arrived at that conclusion, read the September 15, 2015 entry in the Captain’s Logs. For a greater in-depth look at the complexities of sub-surface oceans, we will now turn to the satellite that started us thinking about this possibility in the first place.

BTW, in addition to working on Cassini, Carolyn Porco also worked on the Voyager missions as well as on the New Horizons mission to Pluto. She has also served as consultant to some movies you may have enjoyed! Read about her in her biography link HERE.

The End of Cassini - a Spectacular End to two decades of Scientific Discovery
It is almost impossible to comment on science in the Saturn system without mentioning some advancement that we owe to the Cassini mission. Cassini launched on Oct. 15, 1997 and settled into Saturn's orbit on June 30, 2004. After many discoveries, Cassini's mission came to an end on September 15, 2017, with Cassini plunging into Saturn. We could dedicate an entire course to the advancement in our understanding of Saturn and it's satellites that Cassini provided, but we can't do that here. Instead we provide you with a bare minimum and suggested that you check this Grand Finale Toolkit which is a good starting pint for exploring Cassini. If you're wondering why NASA chose such a spectacular ending, well, here is the reason as stated on the website:

Why End the Mission?
By 2017, Cassini had spent 13 years in orbit around Saturn, following a seven-year journey from Earth. The spacecraft was low on the rocket fuel used for adjusting its course. If left unchecked, this situation would have eventually prevent mission operators from controlling the course of the spacecraft.
Two moons of Saturn, Enceladus and Titan, have captured news headlines over the past decade as Cassini data revealed their potential to contain habitable – or at least "prebiotic” – environments.
In order to avoid the unlikely possibility of Cassini someday colliding with one of these moons, NASA chose to safely dispose of the spacecraft in the atmosphere of Saturn. This ensured that Cassini could not contaminate any future studies of habitability and potential life on those moons.

You will not be surprised that we will visit icy satellites again when we talk about the possibility of Life in Module 5.

For now we'll leave you with 2 short video clips. Here is a NASA video about the Grand Finale:

And if you wondered how a bunch of scientists felt about the end of a mission to which they dedicated a large portion of their professional life, check this 1 minute video: