Interesting item in the science plan kernel (S16) just released to the NAIF website:

OBSERVATION_ID: S1629

SEQUENCE: S16

OBSERVATION_TITLE: Plume Search

SCIENCE_OBJECTIVE: Hope to detect/observe plumes, whether from volcanic activity or geysers.

OBS_DESCRIPTION: Point and stare.

SUBSYSTEM: ISS

PRIMARY_POINTING: ISS_NAC to Enceladus (0.0,5.0,0.0 deg. offset)

REQUEST_ID: ISS_018EN_PLUMES001_PRIME

REQUEST_TITLE: ENCELADUS Geyser/Plume Search

REQ_DESCRIPTION: 1;ENCELADUS Geyser/Plume Search 1x1xNPp -- 3 different exposures

BEGIN_TIME: 2005 NOV 27 19:00:00 UTC

END_TIME: 2005 NOV 27 20:00:00 UTC

Here's the view of Enceladus during the plume search tomorrow:



Both Saturn and the sun are on practically the opposite side of Enceladus from Cassini during the observation (sun phase angle 162 degrees; Saturn phase angle 164 degees).

The sub-Cassini point on Enceladus will be 0.8 degrees N, 171 degrees W--so the limb is approximately the 81W/99E meridians.

Looks like they need to use the serendipity filter.

Thanks for all these informations, jmknapp (also in other threads).
Really hope search will be succesfull!

Here's a comparison to theplume search they did on Feb. 17, 2005:



That was somewhat further away than today's observation (282,000 km vs. 183,000 km) and the solar phase angle was a bit less (154 degrees), also a bit more saturnshine (129 degrees). So today's observation is more favorable all around.

Here was the result of one long-exposure NAC image Feb. 17th:

that is a nice image… not color right? and i assume that blast there is just a light flare?

Only false color images from different exposures (no filters), like this one...
Click to view attachment
For previous discussions on these images, look at
http://www.unmannedspaceflight.com/index.p...findpost&p=5657

Images Up.



http://saturn1.jpl.nasa.gov/multimedia/ima...heQ=0&storedQ=0

http://saturn1.jpl.nasa.gov/multimedia/ima...6/N00043446.jpg

One plume per stripe?

Possible plume? Doesn't look like a lens flare.

Amazing images!!!
IMHO, these prove, without a doubt that there's some very significant venting occuring on Enceladus. I could go on calling them genuine eruptions (Io, anyone? ) as well, the choice of rotating the spacecraft to discriminate from the possible scattered light problems was also very ingenious.

Most definitely one of the most significant Cassini results as of yet. Detecting outgassing is one thing, seeing it is completely different!



EDIT: Looks like Rhea won't be prime news even in this rev, actually devoted to its close flyby

This is the first time I see something like this that is not obviously an imaging artifact.

What's interesting is that the spacecraft has been rotated to make recognizing artifacts to due scattered light within the camera easier. I find it extremely interesting that the possible plumes appear roughly identical in all of the images despite the varying rotation. Also in the overexposed images a very large 'cloud' appears that does not appear next to the nightside limb (only against the bright limb) so this cannot be a diffuse ring in the background.

Still not totally convinced these are plumes but this looks very promising.

I am at work, or I would do this myself, but someone ought to try matching them up to a map - if the bright area match tiger stripes, I will be fully convinced, and Enceladus will join the Io-Triton club of moons in my book.

Is there enough pics for a animation?

I'm at work too but the first thing I'll do at home is use the SPICE kernels to make a computer rendering with a lat/lon grid. Unfortunately my planetary renderer (written by me) is in a state of chaos at the moment because I'm adding some new features to it but hopefully I can make it work fairly easily for this special occasion. Murphy's law at work...

Here's what I get using SPICE data and artificially illuminating the dark side:



The NAC image is rotated from that above (which is oriented with the north pole up), but the "plume" appears to be in about the center of the crescent, which would place it very near the south pole.

Another south pole hot spot?

Here's the corresponding raw image, rotated to about the same crescent orientation:



link to raw image

ohmygod!!!!!!!!!

I had no idea they were planning this. I checked the raw images this morning and I'm still pulling my jaw (metaphorically) off of the floor.

I'm rarely at a loss for words. This is no artifact, no lens trick, this is the real deal.

Whew.

I'm not as up on the entire archive of Enceladus images as I should be, but do we have a set of earlier images of the south polar region?

--Bill

Too bad there isn't plume evidence on the dark limb though, rather than just where one might expect a "diamond ring" effect?

I suppose it would really be an overkill, but I figure a precise way to match the viewing geometry would be extracting the S/C velocity vector relative to Enceladus from the kernels and comparing it with one of the long star trails visible in the background. It would probably be too much work, but might be interesting to see if it's doable.

Anyhow, even this is accurate enough to conclusively say the plumes (plural!) are coming from the vicinity of the south pole.

In my mind, there's not a tiniest bit of doubt whether the feature we're seeing is real. The nail in the coffin to the nay-sayers would probably be a WAC shot which, I predict would show the very same plumes.

Well, if you consider the plume is not hot silicate lava but rather water wapor, I'd be in fact surprised to see it glow in the dark!

Yeah, it's enough to make a jury consider acquitting... but I think this is a clincher for anyone who doesn't want to pop the champagne prematurely: Instead of one flare due to a bright limb, there are three distinct ones, with darkening inbetween. If we were merely seeing supersaturated brightness bleeding out, why wouldn't it bleed in the areas between the plumes, too? After all, they have more bright limb near them than the two outer plumes do.

This is a done deal -- Enceladus is venting. Now the interesting questions are: What is the shape and volume of the reservoir that is providing the fireworks? What is the access from subsurface to surface? And can we drop a submarine in there?

But any vapor on the dark-limb side might only have to gain a little altitude before it was in sunlight?

Why do you insist on the plumes originating from the dark side? There isn't much evidence to support this. In any case, if it were on the dark side, when it rose to get into sunlight, it would probably appear to be practically in front of the sunlit crescent, due to the very high phase angle.

In the light of the recent discovery, I think we'll need to re-analyze the Feb 17 high phase, outbound observations. There was one suspicious cloud-looking thing above the south pole also present back then, but it was attributed to scattered light/overexposure.

What is the power source for this?

{Wild speculation alert}

There is a small asteroid, Toro, that was until about a 100 years ago, in a resonant orbit around the sun with Venus. Since then it has been in a resonance with earth.

IIRC, the transition period took several years.

Is there any feasability that Enceladus is doing something similar with other moons of Saturn? Could Enceladus have an orbit around Saturn that periodically swaps resonances with 2 other satellites? Perhaps the period 'overshoots' slowly one resonance and oscillates back towards another which it overshoots and repeats the process. We see the plumes as powered from the internal heating from the times the resonances are strong and flex the crust (like Io), but our observations are in a time period between and we don't calculate that Enceladus is currently in a resonance.

I don't have the math skills or theoretical background to evaluate this.

What other possibilities exist for heating Enceladus? Radionuclides seem most unlikely, residual heat from an impact would seem to be something that would dissipate very rapidly. Solar heating of an object with an albedo of 1 is ruled out.
Formation heat should have dissipated billions of years ago. Electrical effects of Saturn's magnetosphere are too weak (by orders of magnitutde).

What else is there to heat Enceladus?

We have visible plumes, what kind of dissipation are we looking at? Megawatts?

Great fun figuring this one out!

In the title of this thread isn't it Enceladus that should be written
edit: oop, already correct, sorry

^^ Fixed

Not insisting, I just said that it's too bad there isn't evidence elsewhere too, rather than just in the center of the crescent.



Sure enough, and lo and behold that suspicious cloud-looking thing was very near the south pole too as you say, and not in the center of the crescent!



In that image north is oriented up.

Dismissed at the time as an artifact? Well, well!

The source of the heat is truly perplexing. I hope they will schedual some gravity runs of Enceladus in the extended mission. Enough to obtain a reasonable handle on mass distribution.

I think that there was always suspicion, but they wanted to avoid the humiliation of announcing a great discovery and then having to retract it.

Here's a map of the south polar region, based on Steve Alber's latest cylindrical projection (click for larger image):



This is an orthonormal projection, so the limb is the equator and the south pole ("tiger scratch" feature) is at the center of the image.

Maybe I am 'seeing' too much into your map, but I keep thinking of Miranda and race tracks. . . . .

Found this image of the south polar region (approximate south pole marked with circle, click for larger image):



raw image

The features seen in these images are located at the south pole. At the time the images were taken, the Sun was directly below Enceladus as seen from the spacecraft, but the spacecraft was roughly in the plane of the satellites. So the center of the bright limb is right about at the south pole.

The ridges and wrinkles in that region are a strong indication of tectonics and therefore heat flow, so it makes perfect sense that there will be venting and visible plumes.

Now to figure out why....

--Bill

I would certainly hope there was a healthy suspicion all along. In the previous forum discussion a few months ago, I expressed some of my own suspicion, even if it was tempered by some ensuing (and perhaps not entirely convincing?) replies.

On another note, I just made a south polar view in a perspective projection, available here:

http://laps.noaa.gov/albers/sos/saturn/enc..._cyl_www_P4.jpg

Stretch Marks?

I'm attaching a rendering I did showing the viewing geometry at 17:38 on November 27, 2005. Cassini took several images at roughly this time, for example these two:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=54839

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=54840

I then rotated one of the Cassini images where the limb is overexposed to match the orientation of the rendered image, resized it to match the rendering size and pasted the plumes into the rendering.

This confirms that the source of the brightest plume (assuming we really are seeing plumes which seems very likely) is near the south pole. The fainter plumes appear farther from the pole. It should be noted that this might be an illusion, the brightest plume might be at the same distance or farther from the pole than the fainter ones if its source is well inside Enceladus' 'disc'.

Yes, a STRONG suspicion (the same I had! )...
Anyway, I tried to code with colors the huge dinamic range covered by 3 images taken with increasing exposure time (N00043435/36/37):

Special release for the Enceladus plume:

http://ciclops.org/view_event.php?id=45

Spray Above Enceladus
http://ciclops.org/view.php?id=1652
this release shows the infamous images from January showing a brighting of the limb of Enceladus. Because this looked similar to artifacts seen at other moons, this was brushed off as an artifact as well. However, more indepth analysis of this sequence of images revealed that the" plume" was in fact real.

Fountains of Enceladus
http://ciclops.org/view.php?id=1688
In perhaps the fastest image release ever, this release shows the new jets found near in the south polar region of Enceladus.

This might help pin things down, assuming I got it accurately. Here's the viewing geometry I think, from the vantage point of an observer 100,000 km directly above the south pole:

This news just released by CICLOPS website

"The Fountains of Enceledus"

http://ciclops.org/view_event.php?id=45

"In a wonderful start to the Holiday season, Cassini imaging scientists are delighted by recent sightings of fountain-like plumes towering above Saturn's moon Enceladus. A fine spray of small, icy particles, emanating from the warm, geologically unique province surrounding the south pole of Enceladus and believed now to supply the material comprising Saturn's E ring, was first observed in images taken back on Jan. 16, 2005. Images of a crescent Enceladus returned by Cassini this past weekend show multiple plumes in striking detail. Stay tuned for future announcements on the sightings of the Enceladus plumes".

check the link for more info and images

What's also striking is how obvious the plumes are - even in the RAW unprocessed images posted online.

Yes, this is a truly outstanding mission highlight !!!

Enceledus has been a mission star almost as bright as Titan. To see those plumes so clearly, and they have been on the hunt !!

NASA/ESA should consider an Enceledus lander to complement a Europa mission and follow-up for Titan.

Looking at the raws I noticed that the whole background of the images is light, not just the plumes. This is especially evident on the overexposed images of encaladus:


Notice how the background space is lighter than the "dark side" of Encaladus. Does this mean that plume material is all around, maybe making up a donut of the material around Encaladus's orbit?

Hurrah for a remarkably effective use of the "serendipity filter"!

Maybe they can name Enceladus' south pole "Serendip"?

The E-Ring is just such a donut of material around Enceladus' orbit, and is probably responsible for the light background as well. See here: http://saturn.jpl.nasa.gov/multimedia/imag...cfm?imageID=808 for a depiction of the E-ring.

Regarding the plume images: Feb 20, I posted:
http://www.unmannedspaceflight.com/index.p...topic=691&st=45

"Regarding the image<s> of Enceladus with a possible plume in the south polar region. There is a series of short exposure images of the crescent on the JPL RAW pictures pages and a longer exposure (posted on the CICLOPS web page as "862-1905-3", cleaned up and without JPG artifacts). An even longer exposure on the JPL RAW pages is N00028218. The images show Enceladus as a thin crescent, illuminated by sunlight from about a 4:30 clock angle and as a fatter crescent, illuminated by Saturn from the 9:00 clock angle.
The unilluminated side of the moon between the crescents is visible in silhouette against a lighter background. This background is *NOT* the ring-lit nightside of saturn, 1.) since the dayside of saturn is to the left and out of the image, and 2.) because all images show stars or nearly horizontal star-trails, all parallel, tilted slightly down to the right, and varying in length in proportion to the exposure. I have to conclude that we are probably seeing the diffuse E-Ring in forward scattering, with Enceladus between the spacecraft and the bulk of the E-Ring.
I'm attaching a composite image with the two images named above, and two spatial-bandpass-filtered enhancements of 862-1905-3. These have been processed to enhance fine detail in the plumelike feature close to the moon's limb, and details further away from the limb. None of the images, including the long exposure N00028218, show any trace of the feature against the darkside of the moon above the sunlit crescent, and structures in the plumelike feature converge on the bright limb just like cometary jets seen at comets Halley and Borelly and Wild. There seem to be maybe 3 "sources" for the main plume-like feature and a fainter single-source plume-like feature to the right.
Except for a faint diagonal line "behind" Enceladus, visible in the last picture, which I suspect is a camera artifact or something, all features in this image seem consistent with the plume-like feature being real, not light scattered by contamination in the camera (which is a problem with the NA camera) or a lens-flare. I would have to see the images of other moons with simlar faux-plume features referred to a couple days ago by a team member (earlier in this thread) and apply contrast stretching and enhancement to them (using clean versions, not RAW's from the JPL website) to convince me this feature is not real and is not active plumes from Enceladus. "

(See original post for the picture)

NOW..... VolcanoPele... tell me again this waas just the same old problem with scattered light in the camera....?

That really was fast! I would have expected at least a week's worth of sleep-overs before you guys would come up with something

Crowing about one's foresight is bad manners, Ed. I should know; I do enough of it.