Starship Asterisk*

Chris Peterson wrote:

Nitpicker wrote:My simple estimation of the pressure at the core of Mimas is ~14.5 MPa. (Based on <mean density>*<surface gravity>*<mean radius>, which works quite well for Earth's core pressure of ~350 GPa.)

At that pressure in Mimas, the phase diagram for water shows ice/solid phase only below 273 K, much like in my kitchen freezer.

Right. The question is whether ice is fluid at that pressure, though.

Nitpicker wrote:My simple estimation of the pressure at the core of Mimas is ~14.5 MPa. (Based on <mean density>*<surface gravity>*<mean radius>, which works quite well for Earth's core pressure of ~350 GPa.)

At that pressure in Mimas, the phase diagram for water shows ice/solid phase only below 273 K, much like in my kitchen freezer.

Nitpicker wrote:I can't tell if you are saying water can or cannot exist in liquid form at high pressure (is water one of the few materials or not)?

I assume you must be saying that water (and other materials) can only exist in supercritical form (behaving like both a liquid and a gas) beyond a certain temperature and pressure.

But are you still talking about a large body as small as Mimas? I'm fairly confident that at some point in between the surface and the centre of Mimas, the conditions might be right for liquid water to exist.

Chris Peterson wrote:

Nitpicker wrote:My reading of the recent study, is that the possibilities are either a somewhat oblong solid core, or a liquid water ocean beneath the surface (but above a more spherical solid core). The (rocky?) core may have a certain fluidity, but I imagine -- without much evidence to back me up -- that would require more energy than would be necessary for a liquid ocean above it. (To me, "fluid" is a term which includes liquids and gases, where molten rock would be a more viscous liquid than water in liquid phase.)

I wasn't commenting on the interior of Mimas, only pointing out that the work looking at the propagation of impact energy through bodies considers fluid interiors, not simply liquid. In fact, the interior of nearly any large body is going to be some combination of solid and fluid. At the pressures found far below the surface, few materials can exist in liquid form (including water).

Nitpicker wrote:My reading of the recent study, is that the possibilities are either a somewhat oblong solid core, or a liquid water ocean beneath the surface (but above a more spherical solid core). The (rocky?) core may have a certain fluidity, but I imagine -- without much evidence to back me up -- that would require more energy than would be necessary for a liquid ocean above it. (To me, "fluid" is a term which includes liquids and gases, where molten rock would be a more viscous liquid than water in liquid phase.)

Chris Peterson wrote:

dlw wrote:There have been studies of impact on spherical bodies containing liquid, e.g., (US) football players' heads. The bottom line is that a significant impact on one side may cause damage on the far side, directly opposite to the impact. If Mimas does have a liquid interior, it might show damage on the other side.

Not liquid so much as fluid.

Mimas's most distinctive feature is a giant impact crater 130 kilometres (81 mi) across, named Herschel after the discoverer of Mimas. ...<snip>... The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas that may have been created by shock waves from the impact travelling through Mimas's body.

dlw wrote:There have been studies of impact on spherical bodies containing liquid, e.g., (US) football players' heads. The bottom line is that a significant impact on one side may cause damage on the far side, directly opposite to the impact. If Mimas does have a liquid interior, it might show damage on the other side.

BDanielMayfield wrote:I wonder if tidal flexing could be strong enough to keep Mimas' interior partially above the freezing temperature.

BDanielMayfield wrote:
I wonder if tidal flexing could be strong enough to keep Mimas' interior partially above the freezing temperature. Or, could the great impact that created the crator Hershel have knocked Mimas' core off center? Or perhaps the remnants of the impacter itself could be unbalancing this moon?

Nitpicker wrote:

Historian wrote:The wobble, could it not just be the rocky center is off center? Liquid water seems unlikely since Mimas has been there for a very long time, at very low temperatures.

Yes, a somewhat oval core is suggested as another possibility in the recent study. Neither possibility has conclusive evidence at this stage.

Historian wrote:The wobble, could it not just be the rocky center is off center? Liquid water seems unlikely since Mimas has been there for a very long time, at very low temperatures.

Ann wrote:

Nitpicker wrote:

geckzilla wrote:For some reason, only one of Saturn's hemispheres has blue skies. It's also very easy to end up with weird fringes when objects are moving around between exposures. That picture of the thin rings in front of Saturn's limb would have used the rings as the registration point rather than the background Saturn. Maybe it's really like that but there's a good chance that the misalignment between channels is emphasizing it, too.

I found the original image release for that picture.
http://saturn.jpl.nasa.gov/photos/image ... ageId=3444

I was just looking for other examples upon which Supportstorm (the final digital processor of the APOD) might have based the colourisation. I was expecting to find more examples of a blue limb on an otherwise golden Saturn and was surprised to find only one. (And apologies for originally providing questionable links in need of replacement, geck -- my Greek extends no further than knowledge of the alphabet.)

I have never seen a blue limb on Saturn. (And as some people know, I look for blue details quite carefully.)

Titan, on the other hand, really has a blue limb. This blue limb isn't visible in all pictures of Titan, but it is really there. Here is one good picture of it.

On the other hand, as I searched for information about the nature about this blue limb, I came across this site. It says that the blue limb on Titan is a layer of haze, and that its true color is ultraviolet, not actually blue.

Ann

Nitpicker wrote:

geckzilla wrote:For some reason, only one of Saturn's hemispheres has blue skies. It's also very easy to end up with weird fringes when objects are moving around between exposures. That picture of the thin rings in front of Saturn's limb would have used the rings as the registration point rather than the background Saturn. Maybe it's really like that but there's a good chance that the misalignment between channels is emphasizing it, too.

I found the original image release for that picture.
http://saturn.jpl.nasa.gov/photos/image ... ageId=3444

I was just looking for other examples upon which Supportstorm (the final digital processor of the APOD) might have based the colourisation. I was expecting to find more examples of a blue limb on an otherwise golden Saturn and was surprised to find only one. (And apologies for originally providing questionable links in need of replacement, geck -- my Greek extends no further than knowledge of the alphabet.)

geckzilla wrote:For some reason, only one of Saturn's hemispheres has blue skies. It's also very easy to end up with weird fringes when objects are moving around between exposures. That picture of the thin rings in front of Saturn's limb would have used the rings as the registration point rather than the background Saturn. Maybe it's really like that but there's a good chance that the misalignment between channels is emphasizing it, too.

I found the original image release for that picture.
http://saturn.jpl.nasa.gov/photos/image ... ageId=3444

KarelVreeburg wrote:What I don't understand is why the so called huge impact crater on this thiny snowball moon has the form of a Hexagon. On some pictures of Jupiter and other planets on the pole area also Hexagons are present , WHY?"

Beyond wrote:Ahh, the golf ball returns. I like Mimas. It looks so... clean and spiffy.