CICLOPS: Cassini Imaging Central Laboratory for OPerationS

Targeting the Jet Sources

The geologically active "tiger stripe" fractures of Enceladus are revealed in unprecedented detail in three high-resolution Cassini image mosaics, acquired during the Aug. 11 flyby. [Press release here.]

Aug 14, 2008: Great Southern Land - This sweeping mosaic of Saturn's moon Enceladus provides broad regional context for the ultra-sharp, close-up views NASA's Cassini spacecraft acquired minutes earlier, during its flyby on Aug. 11, 2008.
Aug 14, 2008: Baghdad and Cairo Sulci on Enceladus - Cassini shot past the surface of Saturn's moon Enceladus on Aug. 11, 2008, acquiring a set of seven high-resolution images targeting known jet source locations on the moon's "tiger stripe" fractures, or sulci. Five of those images are presented in this mosaic.
Aug 14, 2008: Damascus Sulcus on Enceladus - Cassini shot past the surface of Saturn's moon Enceladus on Aug. 11, 2008, acquiring a set of seven high-resolution images targeting known jet source locations on the moon's "tiger stripe" fractures, or sulci. Two of those images are presented in this mosaic.
Alliance Member Comments
TomMadigan (Aug 26, 2008 at 2:21 PM):
Andrew Brown (3488) and NeKto:
Thank you for the affirmation. You’re absolutely correct concerning the mass of Saturn vs. Jupiter. I was speaking in “Powers of Ten” and had probably taken undue license with the values (Saturn: 5.7 x 10^26 kg and Jupiter: 1.9 x 10^27 kg) as they are not that dissimilar. As far as answering your questions, Carolyn did a fine job ;)

Carolyn; thank you.
Re: Roche Limit; Rather than overcomplicate my answer, I deliberately neglected to mention that the strict formulation of the Roche limit only applies if gravity is the sole force binding the moon together. A newly formed moon or planet that has just coalesced from smaller planetesimals would be a good candidate for breakup if it came too close to a larger body. Aside from internal cohesiveness, another possibility could be a range of densities among the various moons. Since the Roche limit reduces to the cube root of double the ratio of the densities of the greater (more massive) body vs the lesser (less massive) body multiplied by the radius of the greater body, those moons of Neptune that are within the Roche limit of Neptune for one moon may lie outside their own Roche limit for Neptune if they have a higher relative density. An interesting scenario would be one where there is a large relative disparity of densities among the moons. The Roche limit of one may lie outside the Roche limit of another of greater density.
Jay55 (Aug 24, 2008 at 11:56 PM):
Hello Carolyn, I was very interested in your explanation of tidal stresses to Nekto and I couldn't help wondering about Neptune's moon Triton. I imagine the same kind of thing is going on there with the geysers discovered by Voyager 2 except they are mainly liquid nitrogen as i found out. How do the lessons learned at Enceladus help us understand what's going on Triton or vica-versa. I know Triton's orbit is retrograde which if i understand correctly makes it more subject to tidal heating. I know you said that tidal heating would be concentrated at the poles but do you think there is any significance that at both Enceladus and Triton the heating is going on at the south pole? Last question. Will there ever be a Cassini style mission to Neptune (my second favourite planet) ? i truly hope to see that in my lifetime? It is been an exciting time to be alive watching Voyager and Cassini thats for sure.
Red_dragon (Aug 23, 2008 at 2:29 PM):
Thanks for letting me know. And I totally agree with NeKto; it's really a pleasure to read your comments. Space explorations needs more people with your skills, so people would see how the universe has so many and exciting things worth to study and discover and it does not stop in just a big picture.
carolyn (CICLOPS) (Aug 23, 2008 at 9:40 AM):
Red_dragon: If the moon has some internal strength, it might survive the tidal forces within the Roche Zone. It doesn't matter how it got in the Roche Zone ... the answer is the same.
NeKto (Aug 22, 2008 at 3:20 PM):
Thanks again Carolyn. you have three talents that i greatly apreciate; you say what i wanted to say better than i did, you remind me of important facts that had slipped my mind, and you add information that goes a long way toward putting the big picture together. thanks for all of that.
one thing that crossed my mind; at the temperature and presure of Enceladus' surface, it would not take a lot of heat to sublimate water ice. But there is a rather substantial ring that has persisted for a rather long time that, by all indications, is fed by material vented out of Enceladus. That adds up to a lot of heat disapated over time. so far the indications are that the jets are continuous. i would find it hard to accept that that amount of heat could be generated within Enceladus without something melting somewhere.
this Saturn system is intriguing as all get out. i'm having a great time trying to figure some of it out, and i'm only playing!
Red_dragon (Aug 22, 2008 at 2:39 PM):
One question about the Roche limit: imagine a body that is still forming and when that's not finished yet one forms close to it, so when the main body has ceased to grow, the second one is within Roche's limit. Could survive that body?
Pipipot (Aug 22, 2008 at 12:22 PM):
Thanks all for the input and Carolyn for clarifying Saturn's m.f. bearing on Enceladus. I've learned a lot. Will any data we have tell us something, e.g. 1)how often the jets occur; 2) how strong/high are the steam; 3) do they occur when Enceladus is closest to Saturn; 4) what happens when Enceladus is farthest from its host; 5) are there steam jetting out from vents during this time; 6) if Enceladus is far from the sun's influence insofar as its freezing & melting of liquid are concerned, would it therefore suggests that Enceladus core is active at anytime? I've arranged these questions in such a way one can discern the answers to some intriguing hypothesiss that have come up with so far.
carolyn (CICLOPS) (Aug 22, 2008 at 10:32 AM):
Everyone: Here are some answers to your questions:

Jay55: We are coming into northern hemisphere vernal equinox soon, followed by northern spring/summer. So the southern polar region is going more and more into darkness. The phase angle will generally be around 90 degrees if we're looking down on the region from above, and we also have to contend with shadows. So things aren't going to get better but worse as time in this mission goes on. But we've already gotten some good views into the fractures where the sources are, and as we've said: if the jets that are active now are leaving any effects on the surface, they are subtle, and probably because the effects we do see are cumulative. We're still working on this issue.

NekTo: Tidal heating will mostly be concentrated in the polar regions to begin with. So your question devolves to: Why the southern polar region only? The degree of internal heating you can get from tidal stresses depends on the material properties. If something flexes easily, the tidal stresses can generate heat; if it is resistant to flexing, then the stresses won't produce much if any heat. The fact that Enceladus' south pole is where all the action is tells us that the material properties within the moon are not axially symmetric, and the volume under the south polar terrain is where the tidal strain is concentrated. Many of us are busy trying to understand why! And we don't really know how close any purported bodies of liquid are relative to the surface. Some ideas for the generation of the jets suggest that they may not derive from liquid at all. However, whether that is correct or not, there is still good reason to believe there is liquid somewhere within Enceladus because otherwise, you have a very difficult time getting enough tidal heating to generate the heat we see. So, it's back to the issue above: if there is, say, a sea of liquid water beneath the south pole, then that would yield more flexure and more heating there.

Pipipot: The magnetic field of Saturn has no effect on the geology or interior state of Enceladus. However, you might be thinking of the magnetic field observations by the Galileo spacecraft at Europa, which gave clear evidence of a salty ocean within that moon. There, the imposed magnetic field of Jupiter across Europa created what we call an induced field in the ocean, and that effect was measured by the Galileo magnetometer. There's almost no chance of that happening on Enceladus, since any ocean would be smaller (since Enceladus is smaller) and Saturn's magnetic field does not rock back and forth at Enceladus like Jupiter's does at Europa...a condition that greatly aided the detection of Europa's ocean's induced field.

TomMadigan: A body straying within the Roche zone might survive being pulled apart by tides if it had some internal strength, as most moons do. There are several moons within the Roche Zone of Neptune, for example, about the size of Prometheus and Pandora, and they are apparently doing just fine.
Jay55 (Aug 22, 2008 at 5:16 AM):
Nekto if you want a schematic of the Saturn System or better still wander around and explore each moon i suggest you download the free program Celestia. Its really cool you can explore every planet/moon in the solar system and follow Cassinis trajectory.
Jay55 (Aug 22, 2008 at 5:13 AM):
Carolyn , Will subsequent flybys of Enceladus be used to image the same areas but with a different phase angle with the sun. I find myself wondering what's down in those valleys/canyons. Perhaps illumination from a different position could directly illuminate the source of the volcanism. Am I right t say that they are in shadow at present. And fantastic images so far by the way. Truly tremendous. I feel truly privileged that I am alive witnessing this first hand.
NeKto (Aug 21, 2008 at 5:28 PM):
TomMadigan and Andrew Brown;
thank you both for the iluminating information. i felt the hypothesis of tidal heating was rather low probability largely because i had no information on the eccentricity of Enceladus' orbit. it would be a great help to me if anyone could put together a schematic diagram of the Saturn system, even tho it would be a small enciclopedia at this point. (my dyslexia is affecting me rather badlt today, please excuse any misspellings)
i am not ready to elevate tidal heating above the leval of hypothesis yet, but there are no better candidates at the moment. i still have the same problem with tidal heating i had when the discovery of the jets was first anounced; why is the heat confined to such a small region? why are there no general signs of wide spread heat distribution? there would have to be some very unusual substructure to explain the limited area of new terain and the abundant evidence of very old terain. That is possible, but how probable?
Mercury_3488 (Aug 21, 2008 at 11:53 AM):
Hi TomMadigan,

Excellent post, describes very well what is going on here. One slight nitpoc & it is slight, is that Saturn has a mass of 95 Earths & Jupiter 318 Earths. So Saturn is just under one third of Jupiter's mass.

Yes you raise Io as a great example. This shows how a similar process affects objects within a huge mass range. Io is the densest moon in the Solar Syatem, approx 3.5 gcm, not a huge amount less than Mars & has a mass of just over 1,000 that of Enceladus.

Enceladus has a density of about 1.6 gcm, so is a real lightweight compared (expected due to the huge bulk of ice) Yet both are predominantly tidally heated.

Andrew Brown.
TomMadigan (Aug 20, 2008 at 2:28 AM):
Pipipot and NeKto:


When trying to answer questions such as these, it occurs to me that we should first look for similarities between Saturn and any interactions with its satellites and similar interactions between its larger sibling, Jupiter and its entourage of satellites. It’s well documented that the lion’s share of the energy that fuels Io’s active volcanoes is derived from tidal heating. Because of its proximity to Jupiter and its orbital eccentricity, Io endures continued tidal flexing from Jupiter’s exceedingly strong gravity. Explained differently, the force that Jupiter’s gravity exerts on Io changes significantly from one point to another (a differential change) along a line connecting the two centers of mass. This differential force is the same “tidal force” that gives us the tides here on earth and is responsible for the harmonious gravitational interplay between the earth and the moon. This tidal flexing induces internal frictional heating and is the primary cause for Io’s active volcanism.

When you consider that Enceladus has an orbital eccentricity almost identical to Io’s and, like Io, is in close proximity to its host planet (Io is the closest of the major Jovian satellites; Enceladus is the second only to Mimas), its no accident that we see evidence of internal heating, heating no doubt caused by tidal flexing. It is quite possible that the Cryovolcanism we observe on Enceladus is caused by very similar processes as that which produces Io’s volcanism. Although the tidal force endured by Enceladus is more than ten thousand times less than that endured by Io, it should be noted that Saturn has only 10% the mass of Jupiter with a density less than that of water. Another factor that figures in significantly here is that Enceladus is at an orbital distance from Saturn that is only 4 times the Roche distance (for Enceladus and Saturn). Any two bodies where the lesser of the two goes inside the Roche limit, that body will be disrupted as the tidal force exceeds the self-gravitation of the body, resulting in its destruction or material disassociation. The closer to the Roche distance, the greater any tidal effects will be.
TomMadigan (Aug 20, 2008 at 0:43 AM):
Gruapma:
Historically (c 800-1050), Baghdad was the intellectual capital of the world while the supposedly enlightened clerics and thinkers of western Europe, up through the mid-17th century, were disemboweling heretics, burning them at the stake or placing them under house arrest for publishing such heresies as heliocentrism and the wild notion that the earth orbits the sun and that we’re not the center of the cosmos (if you think what they did to Galileo was bad, look up Giordano Bruno when you have a spare moment). Among the disciplines the ancient Persians (the people of Iraq and Iran) studied, Astronomy and Mathematics (Algebra was first developed by them as was the numbering system we use today) were first and foremost with Baghdad being the center of learning and study. Its no accident that 2/3 of all stars with proper names have Arabic roots. Because the scientists, thinkers and philosophers of this culture did most of the work they got to name the stars and influence the study of that discipline going forward. Baghdad remained the center of science and learning up through the late 11th century until an influential Muslim cleric, Al-Ghazali, determined that mathematics was the work of the devil (sound familiar?) and, unfortunately, Baghdad and the enlightened culture that it represented never recovered.

Historically (at least from a Western perspective), the languages of science were Latin and Greek. You’ll note the names on all the published maps of the terrestrial planets are in Latin (ex. Olympus Mons – Latin for the mythological Greek mountain that was home to Zeus, Mount Olympus). These ancient languages, along with the Arabic tongues, have been the languages of science. This brings me to your question; as an American, I don’t take it as an insult that Arabic names are used but more as a continuation of the scientific tradition of old.

As an aside, a little known casualty of the ongoing conflict in the Middle East was the near destruction of the Iraqi National Observatory on Mount Korek, first by the Iranians and then by the USAF during GW-II – look it up.
NeKto (Aug 19, 2008 at 12:35 PM):
Carolyn; there is always that chance that something obvious will show up on the next image. if the team didn't see anthing obvious on this set, then we didn't get that lucky this time. Guess you folks will have to do some more "work" to get the big fun out of this ice ball. (but the fun so far is well worth it!)
i was able to see the "older" terain next to the active suci with a great deal more clarity. i can't tell if those "old" stripes are remnants of formerly active sulci or if the "chapped lips" as one of our other members described them migrate outward from the active sulcus. unless i am drasticly misreading what i see, those two hypotheses have to cover the majority of probabilities for the formation of what i see.
Pipipot, the magnetic field of Saturn is symetric as far as Enceladus is concerned. any efect on the south side should be the same on the north unless there is substantial ionization. not very likely at the temperatures of the big ice ball. we don't know how deep the melting is yet, other than it is close enough to the surface to vent. how close does the liquid come to the core? I haven't got enough information to even guess. But i think your questions are good from a non-scientist. sounds like you are having as much fun with these images as i am!
Pipipot (Aug 19, 2008 at 11:40 AM):
These are great pictures for us to contribute food for thought. I am not a scientist and do not have any background in geology nor astronomy. But is it something to think of the position of Enceladus against Saturn where the later's magnetic field imposes pressure on the moon from the north if this part is tilted toward the planet that is why the vents are down in the south hemisphere. Also, icy materials inside are melted closes to the core so much so the liquid looks for vents to get out? I invite others to comment since I am not familiar with any of the things I just mentioned.
carolyn (CICLOPS) (Aug 16, 2008 at 2:23 PM):
NeKto: That is indeed the big question, and the whole point of taking these images. But we don't have an answer for you yet. The problem may be that we don't yet know how to unequivocally recognize the effects of the process that produces the jets. For example: What geological landforms should we be looking for? Could the process be so violent in its early stages that it throws blocks all over the place, or are the blocks created by tectonics and erosion? We have some analogies we're working with, and there is a lot of discussion across the team about this right now. But it will be a while before we come to any conclusions, or even any satisfactory hypotheses that most of us think stand a chance of being correct.

No one said this would be easy, you know!
NeKto (Aug 16, 2008 at 1:05 PM):
Carolyn; well said. the question that keeps jumping out at me, as i look at all the information in these extrordinary images, is this; is there anything here that gives us any indication what is powering the vents? from where i sit that is the big question. by the way, the results far exceded the anticipation!
ultomatt (Aug 15, 2008 at 11:50 PM):
It occurs to me that the block distribution might have a direct relationship to the low gravity, which according to Wikipedia is 0.0113g...one ton would tip the scales at about 22 pounds. The block distribution takes on a different character under such a low gravitational field.
Just a thought...

Matt
carolyn (CICLOPS) (Aug 15, 2008 at 5:07 PM):
Alliance Members: I have been very gratified that over the time that our CICLOPS Alliance Members' comment sections have been alive, there have been no `flame wars' of any kind or any of that childish behavior on our site. So far, the commentary has all been high-minded, the questions have been intelligent, provocative and educational, and it's been a pleasure to logon in the morning and see what all of you have been doing, thinking, questioning, etc. I VERY MUCH want to keep it that way.

So, absolutely keep any insults to yourself. And other than space exploration politics, please keep any such sensitive political commentary out of these pages. I will take it upon myself to delete such non-sense should it start to appear.

Remember: we are all outrageously fortunate to be able to live through this moment in time, when we can actually see things that no human has ever seen before. Just think: someday, we will have seen it all. But that's not true right now. We still have great adventures ahead of us. And I think if we all focussed on the significance of that, you wouldn't feel the need to even waste your time thinking bad thoughts. There are too many good thoughts to occupy us for a long time!

So, be good.

I'll answer some of the questions you have when things have quieted down a bit. As I understand it, our findings at Enceladus this past week are going to make it to the New York Times tomorrow. For us scientists, that's a BIG deal.

Onward!
Red_dragon (Aug 15, 2008 at 2:52 PM):
Good work!. Finally we know where erupt those geysers. No doubt it will be interesting to know the origin of that boulders.

The most amazing thing of the flyby besides of the images and the results is how a ship that is so far that her transmissions need more than a hour to reach Earth has been able to do that thing. Sometimes, it's hard to believe that's real and not just sci-fi (Still wondering why I call Cassini the "Supreme Explorer"? :).

A question: you gave us a terrestrial example of the difficult maneuvers Cassini had to achieve. Could an archer or a shooter to do something similar or it's something really epic?. Sorry if the question is weird, but I'm curious about it.

To Graupma: what's the problem on naming geographical accidents on another worlds (not only Enceladus, but also -I think- Titan) by something that just SOUNDS as Muslim, when as emmy has stated are names of cities that existed BEFORE Islam?.
I recognize I'm from outside the US and my POVs are quite different of the US ones, but come on... don't merge that stuff with science.
demmith (Aug 15, 2008 at 2:45 PM):
emmy: I'll second your comments to graupma. Its too bad that in the midst of this great scientific and technological achievement we have to endure a post from one whose existence is an insult to humanity. Back to business...

I can't wait to see more analysis of what is in these photos.
emmy (Aug 15, 2008 at 11:48 AM):
Can we expect more pictures of Enceladus? I forget, but how long do the jet streams erupt?

The pockets - Are we sure that they are pockets or boulders? I remember a mention that the different colors were related to ice density.

Graupma,
They just made this huge discovery and you're concerned about them naming the sulci after several of the oldest cities in human history - that were around even BEFORE Islam? Really? Two of them are Egyptian, even. I fail to see the insult. They even stated that "Features on Enceladus are named for characters and places from "The Arabian Nights," and the four most prominent sulci are named Alexandria, Cairo, Baghdad and Damascus." That would be a literary piece not even remotely related to the Muslim belief structure.
graupma (Aug 15, 2008 at 10:31 AM):
Why do you use Moslem and middle eastern names to identify areas on this and other satellites? why? What an insult to all the work that U.S. money and taxes have donated to your efforts.
Rich777 (Aug 15, 2008 at 8:37 AM):
The mosaic sort of reveals the moon as being frozen. Not as drastic as Europa, but a chilly place none the less. Excellent images people!
demmith (Aug 15, 2008 at 5:47 AM):
Just to the left of the Baghdad Sulci (I) there is a bright white area. It looks as if it is at the bottom of the trench or is it an optical illusion and is a raised area shining in sunlight? Looks intriguing anyhow.
volcanopele (Aug 14, 2008 at 9:25 PM):
Given their size, they are more than likely boulders. Boulders can be created through many processes: impacts breaking up the upper layers of the surface, tectonic activity grinding the surface into smithereens, mass-wasting (chunks of bedrock moving downslope), or volcanic/cryovolcanic activity blowing boulders out of a vent. The Imaging team is still looking at the distribution of boulders seen in our highest resolution images to determine the origin of those seen in these images.
Spaceman (Aug 14, 2008 at 7:42 PM):
In the Baghdad and Cairo Sulci on Enceladus image (PIA 11114) the entire surface seems littered with little pockmarks. In other words, from above , the surface looks littered with bolders. They seem so evenly distributed across the image and are present on peaks and valleys. Does the Ciclops team have any idea what those might be?

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