Enceladus

Evil Dr Ganymede · Post #1by **Evil Dr Ganymede** » 17.01.2005, 18:39

http://saturn1.jpl.nasa.gov/multimedia/ ... 026570.jpg
http://saturn1.jpl.nasa.gov/multimedia/ ... 026534.jpg
http://saturn1.jpl.nasa.gov/multimedia/ ... 026481.jpg

This is a hemisphere of Enceladus that has not been previously imaged...
(you can find all the latest raw images - including some really nice ones of Mimas and Dione - here now, since they moved them temporarily from the Cassini site due to Huygens)

But get a load of that surface - looks like something very strange has been going on at Enceladus, there are barely any signs of craters and instead there's lots of grooves and ridges!

Spaceman Spiff · Post #2by **Spaceman Spiff** » 17.01.2005, 19:05

In the third picture, I spy one (1) small, lonely crater! So, Enceladus is a bit Ganymedian, then, Evil Dr? There are two close Enceladus encounters on 9 and 17 March, aren't there?

Spiff.

Dollan · Post #3by **Dollan** » 17.01.2005, 19:06

How smooth! Isn't Enceladus located at a particularily thick ring or some such? There must be some kind of subsurface activity; I wonder if gravitational flexing is enough to account for it. Could we be looking at a mini-Europa?

...John...

Evil Dr Ganymede · Post #4by **Evil Dr Ganymede** » 17.01.2005, 19:11

Spaceman Spiff wrote:In the third picture, I spy one (1) small, lonely crater! So, Enceladus is a bit Ganymedian, then, Evil Dr? There are two close Enceladus encounters on 9 and 17 March, aren't there?

Spiff.

Enceladus is much smaller than Ganymede though - 500 km radius vs 2634 km radius. We know that part of it was resurfaced from the Voyager images, but not to this extent... (as to why it was resurfaced - beats the hell out of me. I'm guessing tidal heating is to blame?). Still, I'd be wary about comparing features on the two satellites, the difference in scale may affect how the resurfacing processes work.

It's pretty awesome though

- can't wait for the closer encounters.

Spaceman Spiff · Post #5by **Spaceman Spiff** » 17.01.2005, 19:39

Evil Dr Ganymede wrote:It's pretty awesome though - can't wait for the closer encounters.

Oh yes, indeedy! But, did you notice from the Voyager piccies the 'clear' evidence of 'plate tectonics' on Enceladus. At least, there was gigantic slip-strike fault (as you commented for Titan) where you could see two parallel rilles were cut in half, and dragged sideways 10's of km apart! (check the Celestia texture for Enceladus (just right of centre)).

That suggests there are commonalinties between Enceladus and Ganymede - and Europa - despite size differences.

What I find more puzzling is the total difference between Mimas and Enceladus - same size, same place, different surfaces... Yum.

Spiff.

Post #6by **chris** » 18.01.2005, 03:26

Thanks for the links to the Enceladus images. The fine grooves and ridges are very striking. My initial reaction was, "Nice bumpmap!" I can't wait for the close flyby on February 17. What an astounding mission Cassini has been so far!

--Chris

Dollan · Post #7by **Dollan** » 18.01.2005, 04:43

Isn't it amazing at how utterly dynamic the Saturnian system is proving to be? I remember when Galileo first arrived at Jupiter, I was thinking how remarkable all of the shots of Io and Europa would be, with their, even then, apparent active geologies. I was pumped about Callisto and Ganymede. I was even excited about those tiny inner moons and the small outer moons that, to my mind, received something of a short stick. Galileo spoiled me.

I'm almost ashamed to say, I was thinking at one point about how *borning* Cassini would be. Saturn and its rings, been there done that. Sure, maybe we'll get to see finer detail in the rings, maybe even some cloud patterns on Saturn itself. But, come on! Aside from some geological oddities, Saturn's moons are ice balls! Titan would be interesting, but it's covered with smog. And the surface... probably it will be just the exact opposite of what everyone thinks. Blah blah blah.

How WRONG I was back then (and, in my defense, those kind of thoughts faded more and more as I actually did some research on the Saturnian system and Cassini drew closer). We have Titan, a moon that might well have an active geology and surface liquid of some sort. An Earth analogue in many ways. Iapetus with its utterly bizarre ridge. Even little Hyperion, sucking matter from the rings like some greedy little school kid trying to finish the soda before his little brother shows up. And now Enceladus, displaying to my eye at least, something possibly akin to an internal activity that is keeping the world in a state of flux.

They're already tsalking about follow up missions to Jupiter and, more specifically, its moons. I certainly hope that they follow suit with Saturn. Imagine what we could learn from a rover, designed to operate on Titan's surface? Or mini-landers on Iapetus, Enceladus, even cracked Dione!

Whew... what an exciting time to be alive.

...John...

Ynjevi · Post #8by **Ynjevi** » 18.01.2005, 07:05

Evil Dr Ganymede wrote:Enceladus is much smaller than Ganymede though - 500 km radius vs 2634 km radius.

Actually it is ~ 250 km radius vs. 2634 radius. Ganymede is over ten times larger than Enceladus.

Evil Dr Ganymede · Post #9by **Evil Dr Ganymede** » 18.01.2005, 07:37

Ynjevi wrote:
Evil Dr Ganymede wrote:Enceladus is much smaller than Ganymede though - 500 km radius vs 2634 km radius.

Actually it is ~ 250 km radius vs. 2634 radius. Ganymede is over ten times larger than Enceladus.

D'oh. I had a brain fart and got my radii and diameters confused

. Sorry.

Michael Kilderry · Post #10by **Michael Kilderry** » 18.01.2005, 09:54

What would we talk about on this forum without Cassini? I think a probe to Uranus and it's moons should be planned next, after the moons of Saturn proved not to be such boring ice balls, who knows what we'll find there.

Michael Kilderry

Evil Dr Ganymede · Post #11by **Evil Dr Ganymede** » 18.01.2005, 17:31

Michael Kilderry wrote:What would we talk about on this forum without Cassini? I think a probe to Uranus and it's moons should be planned next, after the moons of Saturn proved not to be such boring ice balls, who knows what we'll find there.

Well, there are these rovers still trundling around on Mars...

Problem with a Uranus mission is that it is damn near impossible to get something in an equatorial orbit around it - you'd have to send a probe out along the ecliptic, and then when it gets there (a) slow it down enough to get it into orbit and (b) change its orbit by 90 degrees to align with Uranus' equatorial plane get it to fly-by as many satellites as possible for maximum imaging potential. That sort of thing requires a LOT of fuel.

Also, it'd take forever to get there, especially if NASA insisted on sending it on another of its 'send it past every other planet at least six times but not the Earth because some idiots are paranoid about nuclear contamination' trajectory.

Evil Dr Ganymede · Post #12by **Evil Dr Ganymede** » 19.01.2005, 00:38

lostfisherman · Post #13by **lostfisherman** » 19.01.2005, 01:02

I did some red/green/blue filter composites with the appropriate raw images, where I was pretty sure the images had the same exposure time (not all of them seem to). Just playing really. They are in what I take to mean 'natural colour', and might be of some interest to look at.

You guessed it, grey as a winter sermon

Rhea, note the very straight line at the bottom

Mimas, getting more and more oval shaped the more I look at it

Enceladus, very interesting white snooker ball

Dollan · Post #14by **Dollan** » 19.01.2005, 01:11

I'm getting more and more anxious for this February fly-by.

...John...

Michael Kilderry · Post #15by **Michael Kilderry** » 19.01.2005, 02:07

Evil Dr Ganymede wrote:
Michael Kilderry wrote:What would we talk about on this forum without Cassini? I think a probe to Uranus and it's moons should be planned next, after the moons of Saturn proved not to be such boring ice balls, who knows what we'll find there.

Well, there are these rovers still trundling around on Mars...

Problem with a Uranus mission is that it is damn near impossible to get something in an equatorial orbit around it - you'd have to send a probe out along the ecliptic, and then when it gets there (a) slow it down enough to get it into orbit and (b) change its orbit by 90 degrees to align with Uranus' equatorial plane get it to fly-by as many satellites as possible for maximum imaging potential. That sort of thing requires a LOT of fuel.

Also, it'd take forever to get there, especially if NASA insisted on sending it on another of its 'send it past every other planet at least six times but not the Earth because some idiots are paranoid about nuclear contamination' trajectory.

Getting a bit OT, but never mind.

To get the spacecraft into an equatorial orbit, you could use the help of the gravity of the moons to cut down on fuel, and you can't let timeput you off a flyby of a remote planet, Cassini took more than a few years to get where it is today, and flybys of Jupiter and Saturn could be used to speed the craft up with the gravity of the gas giants, as well as something interesting to look at along the way.

For Neptune, I wonder if New Horizons could be extended to include a flyby of it and it's moons?

Michael Kilderry

Dollan · Post #16by **Dollan** » 19.01.2005, 04:57

As far as I know, New Horizons will perform a fly by of Jupiter, but until Pluto other planetary encounters are not in the cards -- or the planetary alignments.

I hadn't realized that it was slated for launch in 2006

Michael Kilderry · Post #17by **Michael Kilderry** » 19.01.2005, 06:58

lostfisherman wrote:You guessed it, grey as a winter sermon

I don't quite think so, I have brung out the colours in the three images and equalised contrast for Rhea and look at what they look like now, although these are not how they would truly look to the human eye, or any other eye in fact:

Wow

, Rhea really does have a red-pinkish colour to it. Does that bright frosty feature have a bit of a purple tinge to it?

Enceladus, in predictable colours, also with a purpley tinge to the south.

Mimas is greenish in colour (strange) also wiith a bit of a pink tinge. The moon is beginning to look like something out of Dr. Seuss' book "Green Eggs And Ham"

Evil Dr Ganymede · Post #18by **Evil Dr Ganymede** » 19.01.2005, 07:26

Michael Kilderry wrote:
lostfisherman wrote:You guessed it, grey as a winter sermon

I don't quite think so, I have brung out the colours in the three images and equalised contrast for Rhea and look at what they look like now:

What you see in your "enhanced" images aren't the "true colour" of these bodies. For one thing, the original images are raw images that haven't been radiometrically calibrated (which basically means that they haven't been corrected for camera/CCD characteristics, so there may be dark or brighter regions in the image that are there due to the camera's response).

Second, I would guess that your image manipulations aren't exactly conserving data. Did you adjust the histogram levels for each RGB image channel? If so, how? And how did you know when to stop adjusting them to get what you claim is the colour that they really look like?

If anything, all you've done is adjusted the contrast to bring out some of the features. But you certainly haven't demonstrated that these bodies would look anything but grey to the human eye (or at least very close to it).

Michael Kilderry · Post #19by **Michael Kilderry** » 19.01.2005, 08:07

Yes, but I never said that these are what they would truly look like. The fact that I was saying that I brung out the colours (I did it by adjusting the saturation) would give you the clue that they aren't true colour, and the post quoted on the page before would also give a hint. But very well, I will label them false colour if you think that this is misleading.

And what I mean by "I don't quite think so" was that the moon weren't totally grey after all.

What do you think of Mimas having a slight greenish tint?

Michael Kilderry

Evil Dr Ganymede · Post #20by **Evil Dr Ganymede** » 19.01.2005, 08:54

Michael Kilderry wrote:Yes, but I never said that these are what they would truly look like. The fact that I was saying that I brung out the colours

Agh, english is your first language and you drop a clanger like that....

You brought out the colours. Or enhanced them. But not "brung out", please. Ack.

And what I mean by "I don't quite think so" was that the moon weren't totally grey after all.

There does appear to be some very slight difference in colouration on Rhea. There seem to be interlinking tongues of grey material and slightly more reddish material in the enhanced image, which don't appear to correlate with visible surface features. I'm not sure which images lostfisherman used to make those though or what (if anything) he did with them, but if this colour difference is real then it is rather intriguing.

That said, on closer examination when I tweak the image that lostfisherman posted, the colour boundaries do follow the image compression blocks. I'll have to look at the original raw data.

But it's really not a case of "Rhea really does have a red-pinkish colour to it" as you claimed. If it does, it's imperceptible to the human eye.

What do you think of Mimas having a slight greenish tint?

I don't think it does. The green channel histogram isn't significantly different to the blue or red channels.