Cassini’s Swoop over Enceladus: First Morsels of Science Coming Back Now

Bonnie J. Buratti
Bonnie J. Buratti

Phew! We made it through the deepest swoop yet down into the plume of Enceladus, the encounter we call “E7″ because it’s the seventh targeted flyby of Enceladus.

But now we have our work cut out for the next few weeks as we pore over the data, painstakingly analyzing every signal to understand the composition of the plume and its structure.

So far, we know the Visual and Infrared Mapping Spectrometer (VIMS) was able to get images and data in a variety of wavelengths of light and saw that the plume extends out to at least 1,000 kilometers (600 miles).

Raw image of Cassini's Nov. 02, 2009 flyby of Enceladus
Cassini captured this raw image on its Nov. 02, 2009, flyby of Enceladus. The camera was pointing toward Enceladus from approximately 10,000 kilometers (6,000 miles) away. Image credit: NASA/JPL/Space Science Institute.
› Full image and caption

We also have striking images of the moon crowned by its glorious plume, which Cassini captured right before its plunge. The images illustrate well that the spectacular plume spewing from the south polar region is composed of many much smaller jets.

The images and VIMS data both show that as the moon becomes less and less illuminated by the sun (similar to when our moon approaches the phase known as “new moon”), the plume gets much brighter. These data will be valuable for understanding the detailed structure of the plume and where it connects to the surface.

We have also learned that the density of the plume appears to be less than half of that predicted. Still, the heart of the plume measured on this flyby was about three times denser than the sparser parts of the plume we flew through previously.

There is more good news. We will be able to do the Enceladus flyby on April 28, 2010, on the spacecraft’s reaction wheels. This means we will be able to perform the Radio Science Subsystem experiment with Cassini’s main antenna to understand the interior of Enceladus under the hot south polar region.

During this experiment, antennas from the Deep Space Network (DSN) on Earth will be tracking the spacecraft to see how much Enceladus tugs on it. By measuring this tug, scientists will be able to answer such questions as: How much is the shape of the moon deformed by tidal forces from Saturn? Is there an unusually dense mass under the south pole? (The higher the mass, the larger the tug?)

We know that heating by tidal forces is what drives the plumes, but we’re not sure exactly how. In addition to a possible liquid subsurface ocean, Enceladus may be harboring a dense mass underneath its surface that helped to start and maintain the moon’s current activity.

Just wanted to share our excitement about the reams of data we’re combing through. Now, back to work!

    19 Responses to “Cassini’s Swoop over Enceladus: First Morsels of Science Coming Back Now”

  1. Pete Goldie Says:
    November 5th, 2009 at 2:06 pm

    “We know that heating by tidal forces is what drives the plumes, but we’re not sure exactly how.”

    … is this now the accepted theory, or a consensus?

    Bonnie J. Buratti responds:

    That tidal heating is the energy source for the plumes is a consensus. It seems to be the most reasonable model to explain the main heat source. However, many details are poorly understood, including: What are the geologic manifestations of the heating? Do plate tectonics exist? Are there additional sources of heat such as radioactive decay? Did some type of event trigger the current heating episode? How long lived is the plume? Does it vary? What is the “plumbing” of the vents? What does the interior of Enceladus look like? How extensive is the underground ocean (if there is one)? Hopefully upcoming flybys will help us answer some of these questions.

  2. Vasilis Dalianis Says:
    November 5th, 2009 at 9:18 pm

    Greetings from Greece dear Cassini scientists and engineers. Like you, I’m excited and fascinated. The first results are extremely interesting. Having said this, I should also say that the fact that an unusually dense mass may exist underneath Enceladus’ south pole has surprised and confused me, since according to a paper written by Francis Nimmo and Bob Pappalardo and published in Nature in 2006 (Francis Nimmo & Robert T. Pappalardo (2006): Diapir-induced reorientation of Saturn’s moon Enceladus. Nature, 441/1, 614-616), low-density material (diapir) may exist, either in the ice shell or in the underlying silicate core.
    Needless to say, all of you are brilliant researchers, and needless to say (again), if I worked with you at JPL I’d be the happiest human in the Milky Way!

  3. Andreas Trupp Says:
    November 6th, 2009 at 3:56 am

    In CAPS FY 2009 Q1, which is linked to the CASSINI-Mission, the following reference to Burch et al. is given:

    “Dione, Tethys, Helene, Telesto, and Polydeuces are found to be significant sources of plasma”.

    Some more details on this apparently revolutionary findings are presented in Geophysical Research Abstracts, Vol. 11, EGU2009-8241-1, 2009, EGU General Assembly 2009:

    “Analysis of Cassini Plasma Spectrometer data indicates that Saturn’s moons Dione, Tethys, Helene, Telesto, and Polydeuces are significant sources of plasma. Observations suggest that interchange injections transport plasma
    from these moons outward through Saturn’s magnetosphere. Unlike Enceladus, none of these moons produces a fully developed plasma torus partly because the sources are weaker but also because the plasma is transported efficiently outward through the magnetosphere by interchange. Efficient ejection of plasma from these icy moons
    may exceed expectations from sputtering. One possibility is that these bodies possess active outgassing as is known to be the case for Enceladus.”

    If these observations were correct, this finding would be far more sensational than the plume of Enceladus, given the fact that those bodies have a diameter of some ten miles or even less (in the case of Polydeuces).

    Why is there no reaction by JPL? Are you afraid these results might be too challenging, and should better be ignored?

    Bonnie J. Buratti responds:

    This information could potentially be important. The activity on Tethys and Dione was reported earlier by Jim Burch of Southwest Res. Inst. and his colleagues in the 14 June 2007 issue of the scientific journal Nature. There was a NASA news release on that day describing the results (see http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20070614/). The preliminary report on the smaller satellites needs to be written up for a scientific journal (where it is reviewed carefully by other scientists) before NASA puts out a news release. NASA scientists are in fact interested in this result, but they feel it needs more study and confirmation before a release.

  4. Leo Kitsos Says:
    November 6th, 2009 at 4:14 am

    I think , life is not easy, but it is so beautyfull ,if You see huge Mars-volcanoes
    the rings of the 4 gas-giants with a mathematic accurancy no one can explain
    , the white mountains of Ganymede, Callisto and Europa and many-many more
    beauty´s of our solar-system, so precious,
    a jewel in the Kosmos.

  5. James Bonner Says:
    November 6th, 2009 at 11:50 am

    Thank you, for your update. The entire Cassini-Huygens mission has provided me with years of fun, inspiration, wonder, and excitement. The flybys of Enceladus during the Equinox mission continues to raise the bar of space exploration. Your discoveries provide fuel for human imagination that links our solar system to findings made by other NASA missions like, Kepler, with more to come. Together, with space agencies from other nations, you are providing human beings with a humbling and unique view of our history and place in the known universe. Your work is profound.

  6. John Says:
    November 6th, 2009 at 9:29 pm

    Awesome results! The Saturn system continues to amaze us. Thanks, and keep up the good work!

  7. Jim Johnson Says:
    November 9th, 2009 at 10:43 am

    Questions regarding E7: Cassini has a plasma density instrument ,charged particles detector and a magnetometer. What were the observations from these instruments before, during and shortly after this observation run? Are both electrons and ions being detected in the plume(s)? In equal numbers? Are they a minority, with a majority of neutral particles present, or were charged particles the majority of the plume constituents? Did magnetic field strength increase or decrease in the course of this run, and could such changes be correlated with the plume location or with particle densities? Thanks! This is one hard-working probe, along with its team at JPL and NASA. I think people want to know as much as you can give them on this long-running experiment! More data and graphs to go with the great photos, please!

    Bonnie J. Buratti responds:

    There are far more neutrals present in the plume than charged particles. These particles are mainly water ice, but CO, CO2 and light hydrocarbons are also there. We haven’t analyzed all the data from the E7 flyby, but in past flybys we’ve detected more electrons in the vicinity of Enceladus than ions, but most of the charged particles are associated with Saturn rather than Enceladus. I double-checked this with my colleague Marcia Burton, who studies the magnetosphere, and she said scientists believe the electrons are absorbed by the ice grains in the plume. Similarly, the magnetic field we see at Enceladus is Saturn’s. This field appears to “drape” around the plume, so the magnetic field intensity gets less in the vicinity of the plumes. The magnetic increases upstream of an obstacle (where the obstacle could be Enceladus or the plume) and decreases in the object’s wake.

  8. John Says:
    November 11th, 2009 at 10:41 am

    When Cassini visits Rhea in 2010, will it be possible to visually establish the presence of rings around Rhea? How close does Cassini need to be to Rhea to visually establish the presence of rings? Was the November distant flyby close enough?

    Bonnie J. Buratti responds:

    Actually, it may be easier to see the rings from further away, since you are seeing the entire ring system when Cassini “stands off” from Rhea. We don’t know enough about the physical characteristics of the ring to say for sure whether we will be able to see it or not during this flyby. Another way we are trying to detect the ring is by a stellar occultation. When a star goes behind the rings, it should be dimmed.

  9. Neal Granroth Says:
    November 13th, 2009 at 7:54 am

    Thanks for the brief update. The Cassini misson is a fascinating project. It is exciting to read about the information being gathered and some of the preliminary interpretations.

  10. Edsel Chromie Says:
    November 13th, 2009 at 4:09 pm

    It is time to consider that the plume is created via an abnormal magnetic field energy stimulating normally invisible gases in the vicinity to a glowing, visible state of excitement instead of a reflection of sunlight from particles of ice or dust. In this concept, no heat is required and any solid particles detected are merely coincidental. This is similar to the abnormal electromagnetic energy at the Earth’s poles combined with the electromagnetic energy radiated from the Sun stimulating the atoms of gases in our atmosphere to a glowing state of excitement creating the aurora borealis. This concept eliminates the confusion of how the heat is created to boil water where the temperature is over 100 degrees below zero and how the “paricles” can be “blasted” 600 miles from Enceladus.

  11. Edsel Chromie Says:
    November 15th, 2009 at 8:56 pm

    To prove that a magnetic field can create the plume of Enceladus, do this: Rub a plastic store bag briskly with your bare hand for ten seconds. This will generate a charge of static electricitry in the plastic material. Then, move this material near an unplugged fluorescent tube in a dark room. You will very cleary see that the magnetic field surrounding the static electricity charge will stimulate the normally invisible atoms of gases within the fluorescent tube to a glowing, visible state of excitement. The faster you move the plastic material past the tube, the brighter the gases will glow.

    Edsel Chromie

  12. Andreas Trupp Says:
    November 17th, 2009 at 4:13 am

    I would like to give a reply to “Edsel Chromie”: Even if the heat production in the interior of Enceladus or elsewhere (perhaps in the interior of a very small body like Polydeuces) were unexplainable by current theories (I guess the consensus is: Tidal heating is doing it for the most part, though we do not know HOW), no progress in knowledge could be achieved by merely giving the riddle a different name. An “abnormal electromagnetic energy” appears as mysterious as does the generation of heat in the interior of Enceladus.

  13. Edsel Chromie Says:
    November 17th, 2009 at 5:35 pm

    I appreciate the reply by Andreas Trupp. If you read the June 24, 2009 “Plume Vent Models” report, you will note that even if the heat problem were solved, models A, B, and C were deemed unlikely while model D is only plausible and model E is still a work in progress. If you perfornmed the experiment I described in my Nov,15 e-mail, you will see very clearly that my concept is a viable and demonstrable concept. The magnetic fields of Enceladus, Saturn and the Sun are well documented and heat is irrelevant. The convegence of these magnetic field currents will absolutely create an are of abnormal magnetic field current.

    Edsel Chromie

  14. Edsel Chromie Says:
    November 19th, 2009 at 11:01 am

    Every Cassini mission team member should be asking “Where is the residue of ice particles around the tiger stripes?” It is 4 years since the NASA advisory of Dec. 6, 2005, which states, “Jets of fine, icy particles streaming from Saturn’s moon Enceladus were captured in the recent images from NASA’s Cassini spacecraft”. It is as though Enceladus lacks any gravity at all to pull these particles back to its surface. And it added “How a 500 kilometer diameter moon can generate this much internal heat and why it is concentrated at the south pole is still a mystery.” My Nov. 15 e-mail offers an absolute demonstration that an otherwise undetectable weak magnetic field surrounding an otherwise undetectable weak charge of static electricity will positively stimulate normally invisible atoms of gases in a fluorescent tube to a glowing, visible state of excitement without any visible residue. The atmospheric gases in the near vacuum of space in the vicinity of the south MAGNETIC pole of Enceladus is identical to the gases in the vacuum of fluorescent and neon tubes.

    Edsel Chromie

  15. club penguin Says:
    December 30th, 2009 at 12:46 pm

    This blog is great! Thanks for your hard work on it.

  16. weddings Says:
    August 1st, 2010 at 6:14 pm

    I should :) be working, Good to see more people writing about planets.

  17. food gift Says:
    October 4th, 2010 at 2:45 am

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  18. Dave Says:
    October 16th, 2010 at 6:29 am

    Greek mythology gives Enceladus her name as the breath of Mt. Etna. Strange this moon of Saturn shows no signs of volcanism, as is on Earth. Venting observed, and being located in the F ring could indicate Enceladus to be a source of Saturns rings. How many other moons at one time have contributed to Saturns rings??

  19. Inkarnacja / Shelter (2010) Napisy PL Says:
    October 8th, 2011 at 5:45 am

    I’m quite positive they will discover a lot of new stuff right here than anyone else!

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