Dione Outgassing Spotted by Cassini?

brellis · Mar 15, 2007

At the Lunar and Planetary Science Conference, Jared Leisner of UCLA (Go Bruins!) announced that Cassini's magnetometer "had sensed a tenuous cloud of material surrounding Dione as the spacecraft flew past it. Leisner estimates that Dione sheds just 6.5 grams of material per second into space — far less than the 300 kilograms per second spewed by Enceladus, but far greater than the 0.4 gram per second that would be expected if Dione were completely inert." There's not enough dust to make the clouds visible to Cassini' cameras, so they must wait for an occultation to confirm the cloud with the Ultraviolet Imaging Spectrometer (UVIS). Those icy moons are a lot more active than anticipated! SkyTonight Article <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

docm · Mar 16, 2007

All the more reason to mount some kind of comprehensive JIMO missions. Hell, Europa alone is worth the cluster treatment. <div class="Discussion_UserSignature"> </div>

3488 · Mar 16, 2007

Hi there. Thanks brellis for starting this fascinating thread!! Yes it is an interesting development. I heard something about this a couple of Sundays ago on the BBC's Sky at Night, presented by Patrick Moore. It is good to see more about this. As said, the outgassing on Dione is pretty small, but vastly more than if Dione was totally inactive. Also said was that in the high northern latitudes (not at the north pole though, as it is still dark there until the Spring Equinox in December 2009) a frost covering on Dione may have been detected. This had not been seen at the sunlit south pole (perhaps seasonal migration, like that on the large Neptune moon Triton??? Also it was suggested that any activity on Dione appeared to be at the North Pole, not the South Pole like Enceladus. Almost certainly, Dione has an atmosphere of some sort. It remains to be seen, if it is patchy, global, variable or permanent. The article in Sky & Telescope, linked to in the opening post by brellis, stated that cryovolcanic flows had been spotted on Tethys. I have seen & collected a huge number of images of all of the major planets & moons in our solar system & I have failed to spot any. Can anyone help me with this? Tethys to me looks ancient, primitive & unevolved. True the Ithaca Chasma is an impressive feature, but that was formed when the interior of Tethys froze & expanded, splitting open the already frozen crust. Nothing much appears to have happened there since (perhaps the formation of the 400 KM / 248 mile wide http://photojournal.jpl.nasa.</safety_wrapper <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

rhm3 · Mar 16, 2007

<blockquote>In reply to:<hr /> The article in Sky & Telescope, linked to in the opening post by brellis, stated that cryovolcanic flows had been spotted on Tethys. I have seen & collected a huge number of images of all of the major planets & moons in our solar system & I have failed to spot any. Can anyone help me with this? Tethys to me looks ancient, primitive & unevolved. True the Ithaca Chasma is an impressive feature, but that was formed when the interior of Tethys froze & expanded, splitting open the already frozen crust. Nothing much appears to have happened there since (perhaps the formation of the 400 KM / 248 mile wide Odysseus Crater) & even the Ithaca Chasma itself is heavily cratered!! <hr /></blockquote> Although Tethys is heavily craterd pretty much across its whole surface, the crater density isn't uniform...there are certain areas with fewer craters that are suspected to be ancient cryovolcanic plains. Perhaps the article is referring to that. But Tethys has been geologically dead for billions of years...meanwhile, these new discoveries on Dione are interesting. Did you say polar frost? I hadn't heard of that before...it would definitely point towards some sort of atmosphere.

brellis · Mar 17, 2007

Dione gets sprayed by fresh ice from Enceladus. Could the traces seen on Dione be related to this sputtering? If the cloud layer on Dione were actually "secondhand smoke" from the Enceladus geyser, I wonder if it would be so dust-free. <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

rhm3 · Mar 17, 2007

I wouldn't count on it being sputtering...seeing as Tethys and Rhea are releasing no more than 0.4g/s of material. Another possible explanation would be a thin atmosphere and frost migration, not dissimilar to Triton (although probably thinner). I'm not sure how that could be maintained on Dione though.

3488 · Mar 19, 2007

Thanks RHM3. That answers one of my questions. Does Rhea have enhanced outgassing? The answer in your last post is no. Rhea looks unevolved, so not surprised (despite its large size). Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

brellis · Mar 20, 2007

hi borman Sorry if this was a false alarm. The abstract was available when I spotted the more surprising headline of possible outgassing, and I didn't read it until you mentioned it. One asks, would the 'secondhand smoke' be so clean on Dione? Is there a quality to the Enceladus output that forms a recognizable signature? Are assumptions being made about the lack of size of the other moons? Remember, Enceladus was supposed to be too small to do what it's doing. Your question about orbital resonance sounds most prevalent here. with lots of respect, Brad <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

3488 · Mar 21, 2007

Hi brellis & borman. I do believe that orbital resonances are at work here. It is true that Enceladus does spray the neighbours with fresh ice. If so, than crystalline ice should also be found on Tethys, seeing as Tethys is the next major moon out from Enceladus. Also it could explain the smooth surfaces of the Tethys co-orbitals Telesto & Calypso. If they were showered by ice particals from Enceladus, the smallest craters would be buried over time & the profiles softened. The same could be true of the Dione co- orbitals Helene & Polydeuces. Perhaps, some of the ice from Enceladus does make it to Rhea. I would expect to find it on Mimas too. It is true that the Jupiter moon Io sprays its neighbours. As borman says, Ionian sulphur has contaminated Europa, but also has been found on all four of Jupiter's closest moons (Metis, Adrastea, Amalthea & Thebe, colouring them red), along with Ganymede & Callisto. However it does seem that Dione does have some activity, although pretty low level. Regarding the Uranus moon Oberon. Very interesting post, thank you borman for posting it. Oberon was clearly shown by Voyager 2, to have undergone some activity in the past. Many of the crater floors have dark material, that has erupted then froze, covering the original crater floors. I would not be surprised if Oberon has extinct cryovolcanoes. Also careful analysis of the images provided by Voyager 2, reveal some softening of some surface features & tectonic faulting on http://uplink.space.com/show</safety_wrapper <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

brellis · Jun 13, 2007

ESA report on outgassing by Dione and Tethys <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

h2ouniverse · Jun 13, 2007

Borman, As I posted recently on Andrew 3488's thread on that suject few weeks ago, I can testify that I recently attended a presentation from MK Dougherty from Imperial College(*) at the EGU in Vienna. She was recalling that their analysis of Saturn's plasma flow Cassini measurements had evidenced a plume from Enceladus (via the asymmetrical deviation of the plasma by Enceladus) long BEFORE the optical observation. And, that they had measured a similar although less ample phenomenon on Dione... They were really confident that visual observations would confim Dione's emissions. (*) EGU2007-A-05413; PS3.0-1TH3O-006 Dougherty, M. K.; Khurana, K. K.; Neubauer, F. M.; Russell, C. T.; Saur, J.; Leisener, J. S.; Burton, M. E. Discovery of a Dynamic Atmosphere at Enceladus from Cassini Magnetometer Observations Jean-Pierre Lebreton attended too this presentation in Vienna, so it is logical that he signed the com at ESA site, that Brellis linked. Best regards.

h2ouniverse · Jun 13, 2007

They clearly stated they measure an order of magnitude lower than on Enceladus. They made their publicity on Enceladus (rightly so), and had just few seconds of the ten munute presentation mentioning Dione. I do not thinkthey should be suspected of manipulation.

h2ouniverse · Jun 14, 2007

Andrew, Congratulations as you thought, Dione and Tethys are officially added to the list of cryo-active bodies. NASA has communicated too. http://www.nasa.gov/mission_pages/cassini/media/cassini20070614.html

rlb2 · Jun 14, 2007

As for Dion, my first post, see image below, on Images of Saturn http://uplink.space.com/showflat.php?Cat=&Board=sciastro&Number=8287&page=38&view=collapsed&sb=5&o=0&fpart=all after I sharpened, added contrast and brightenened the images back on 07/21/04 was Dione, don't know about the haze? Now we may find out that maybe it was something to investigate??? Saturn's moons Tethys and Dione are flinging great streams of particles into space, according to data from the NASA/ESA/ASI Cassini mission to Saturn. The discovery suggests the possibility of some sort of geological activity, perhaps even volcanic, on these icy worlds. The particles were traced to the two moons because of the dramatic movement of electrically charged gas in the magnetic environs of Saturn. Known as plasma, the gas is composed of negatively charged electrons and positively charged ions, which are atoms with one or more electrons missing. Because they are charged, the electrons and ions can get trapped inside a magnetic field. Now, Jim Burch of the Southwest Research Institute, USA, and colleagues have made a careful study of these events using the Cassini Plasma Spectrometer (CAPS). They have shown that the direction of the ejected electrons points back towards Tethys and Dione. "It establishes Tethys and Dione as important sources of plasma in Saturn's magnetosphere," says Burch. Until this result, among Saturn's inner moons only Enceladus was known to be an active world, with huge geysers spraying gases hundreds of kilometres above the moon's surface. "This new result seems to be a strong indication that there is activity on Tethys and D <div class="Discussion_UserSignature"> Ron Bennett </div>

brellis · Jun 15, 2007

I like the "snowplow" concept. As Dione/Tethys rotate,revolve and bulge, some of their acquired E-ring material falls back off. Was it not already postulated that Enceladus reacquires its own ice as it progresses in its orbit? <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

3488 · Jun 15, 2007

Thanks rlb2. Do I have your permission to download your image? As with your Mars & Io images, I am extremely grateful for your efforts. That haze. Knowing how thorough & careful you are, I suspect that it might be real. Maybe Tethys too? Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

rlb2 · Jun 15, 2007

Do I have your permission to download your image? No problem Andrew, I tried the same effect on some of the most recent images and thus far couldn't come up with the same results. Still looking to verify new images, also looking for out-gassing explosions - stay tuned... <div class="Discussion_UserSignature"> Ron Bennett </div>

3488 · Jun 15, 2007

Thanks rlb2. I do not know what the anwer is. I do however trust you & your images, so if you found a haze, then IMO it exists. Andrew Brown. <div class="Discussion_UserSignature"> "I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before". Linda Morabito on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.http://www.launchphotography.com/ http://anthmartian.googlepages.com/thisislandearthhttp://web.me.com/meridianijournal </div>

h2ouniverse · Jun 15, 2007

Brellis, True, but Enceladus also reacquires directly (ballistically) the heaviest paricles sputtered by the cracks, because the heaviest ones have a speed lower than the escape velocity. So you might as well have this phenomenon on Tethys or Dione (which have larger gravity fields), accounting for some high-albedo areas. I am not sure you can discriminate easily exogenous accretion from endogenous re-accretion.

h2ouniverse · Jun 15, 2007

Borman, As far as I understand, the paper In mentionned was for Magnetometer observations, and for the asymmetrical deviation of the plasma torus, assumed due to a stream of expelled material. If this was accretion, why should it produce an asymmetrical stream?

brellis · Jun 15, 2007

hi H2 Enceladus also reacquires directly (ballistically) the heaviest paricles sputtered by the cracks, because the heaviest ones have a speed lower than the escape velocity. So you might as well have this phenomenon on Tethys or Dione (which have larger gravity fields), accounting for some high-albedo areas. I am not sure you can discriminate easily exogenous accretion from endogenous re-accretion. That makes good sense, too. Perhaps both processes occur on all three moons -- exo and endo. Is there a clue in the size of the particles being emitted? Would geysers send bigger balls of ice out than secondhand-accreted or snowplowed material that simply falls back off in the course of an orbit? <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

h2ouniverse · Jun 16, 2007

Brellis, If I remember well, the size is rather small. I will find the paper that studied that point (not on the top of my mind). But it's W.E. and the answer is on my computer at a my office. The particles below escape velocity fall back as snowplow (ballistic trajectory). The most visible part of the plume is made by such particles. The ones that escape to form the E-ring are not visible...

h2ouniverse · Jun 16, 2007

Borman, OK but the particles deflected by potential lunar mag field should evidence symmetrical trajectories. And this asymmetry has been correlated on Enceladus with the southern pole plumes (once they were discovered)... (note: here I am not talking about the plasma measurements but the magnetometer measurements) So if they detect such asymmetry on Tethys and Dione, isn't it a clue? Regards.

rlb2 · Jun 17, 2007

I do not know what the answer is. I don't know either, for Dion it could be sporadic eruptions coming from one of the thousand of craters on it surface like the ones below... I substantially darkened, sharpened, and added contrast to the images below to help bring out more detail. The bottom image approximately left of center kind of looks like an eruption coming out of a crater, to verify that another image needs to be taken at the same angle to see if that explosive like effect is not an illusion. It is important to note that these images were taken with different filters. Another far out thought is that the new plasma reading are from impacts from ring material into Dion and Tethys that produces orbit escaping material that produces a similar effect as outgassing... Image references below from top to bottom: N00077778 N00081673 N00081691 <div class="Discussion_UserSignature"> Ron Bennett </div>

brellis · Nov 16, 2007

The lower right center of this Cassini pic shows a white splop emanating from the interior of a large (darker) crater. Innocent question: is there a gray area of classification between the categories of Enceladus-style outgassing and a kind of impact reaction where something big strikes the surface and it triggers a delayed outgassing? Edit: or, is the white mark simply a small new coating of debris from a lesser impact inside the big crater? <div class="Discussion_UserSignature"> I'm a recovering optimist - things could be better. </div>

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