If we consider presence of the liquid mantle, the surface of Pluto is mobile and stationary equipotential surface.
Thus the pressure on the entire surface of Pluto is the same (if not to take into account weather events) including stationary tidal Charon forces.

Not sure about that.

Earth's oceans are liquid, and mobile, and a gravitationaly equipotential surface. (Always 90' to gravitational lines of force.)
At high tide, gravity pulls 2 metes of water onto the shore, the pressure on the surface of the beach sand increases due to 2 meters of water.

Consider a trampoline as an equipotential surface. Imagine 2 scales on a trampoline.
One has no one standing on it. I reads "o kg".
The other has Andre the Giant standing on it. It reads "ouch, get off". And the reading is 240kg.

They are equipotential, (same surface curvature), but the scalar readings are different.

The key word is 'stationary'.
The ocean and the atmosphere on Earth lag behind rotation because of the nonstationary, so the pressure can vary. Rotation of Pluto is Synchronized with Charon, therefore is stationary equipotential surface, molecules of the atmosphere have identical energies, and according to the Boltzmann law pressure is the same everywhere.

This weekend we got a CGI-generated flyby animation:

http://pluto.jhuapl.edu/Multimedia/Science...mp;image_id=266

http://photojournal.jpl.nasa.gov/catalog/PIA19873

--Bill





(added Photojournal Link)

Ok, it think I understand - with a liquid mantle Pluto's surface would be in gravitational equilibrium, e,g, a prolate spheroid,
and the atmosphere would be in gravitational equilibrium, prolate, so pressure is evenly distributed.

https://en.wikipedia.org/wiki/Spheroid

Fast spinning planets become oblate, tidal distortions prolate.

My mistake making an stated assumption; that Pluto and its atmosphere are different shapes.
If Pluto is a sphere, but the atmosphere is distorted by Charon's gravity into a prolate shape,
then there should be gravitationally induced static high pressure areas.

If when the planet and atmosphere have the same shape, spherical planet with a spherical atmosphere,
prolate planet with a prolate atmosphere, then there are no gravitational effects on the atmosphere.


That question, "is Pluto sphereical?" was asked, at the press conference,

I think a question to be asked is are Pluto or Charon truly spherical - if they are distorted that might be a clue to something going on inside - or if not that that isn't related to the young surface. Now that they measurements are more precise is there a chance of a pole vs equator (and perpendicular to Charon-Pluto vs along C-P) differences...

Has there been an answer to whether Pluto is spherical or not?

I think that Sputnik planum rises above plutoid even (equipotential body very similar to the oblate spheroid), that is a highland, therefore there are several other conditions than the rest part of surface, and this leads to another conditions of sublimation / condensation.

I don't know about any official word from the team, but I've noticed its disc is very nearly circular. I didn't even account for any asphericality (I'll pretend that's a word) when I was unwrapping the atmosphere from LORRI images to look at the gradient, and didn't have any problems so it couldn't be too far off spherical.

I decided to look a little more into how spherical Pluto is, based on LORRI imagery.
Working from code I'd written for unwrapping the atmosphere from Pluto, I wrote some software to "unwrap" the entire planet.
Pulling from all 3 partial-disk backlit LORRI images, here's the surface of Pluto.

Each pixel across the horizontal axis represents 1 degree. Each pixel along the vertical axis equals one pixel's distance from (my best estimate of) the center of the planet. The bottom of the image is the center of the planet. Dark red pixels are where no samples landed (mostly representing areas that were out of frame, but also areas very near the center, where there were few pixels to go around, so, artifacts of the binning close to the center).
From this, I roughly estimate 3 pixels between max and min surface out of about 662 pixels radius.

I applied the same technique to lor_0299123689, by itself (again, with my best estimate of the planet's center), so that a set of backlit images wouldn't be my only sample.

You have a boundary here consisting of both terminator and limb. I've shifted the plot over so that the area bound by the limb is near the middle of the image, with the terminator-bound areas near the edges. The bottom is still the estimated center of the planet. Isolating a 170-degree section of limb, I roughly estimate about 1 pixel between max and min surface out of about 307 pixels of radius.

Edit (2015-09-01): Here's the same process applied to lor_0299147641, the best image in SOC of Charon with limb. My confidence in my estimated center for this one is considerably lower than for the others; Charon isn't nearly as smooth as Pluto. I'm pretty confident I located it within 2 pixels, though.

I horizontally interpolated the gaps near the center (bottom of the above image) this time, rather than painting them red. I identified a 180-degree section as being limb and estimated about 5 pixels between max and min surface out of a radius of about 261.5 pixels.

Optical geometrical distortion will make the image of the disk nonspherical to some extent if it's off axis.

Doesn't LORRI have some magical set of lenses that limits distortion to less than 0.5 pixels at worst? Or am I getting it mixed up with a different imager?

Edit: To clarify, I'm not disagreeing with your statement; it's certainly a correct one. I've been operating under the assumption that this great lens system made it possible for me to ignore distortion, for the most part, as long as I'm just producing rough estimates. Potential error in my estimates of Pluto's center in these images might be more than the maximum distortion, so I wasn't planning to account for distortion until the raw, uncompressed data were published in PDS. Now that you bring it up, however, I guess I should do some reading to make sure I haven't been thinking of a different imager this whole time.

Sputnik Planum does not appear to be a highland because at its southern end it is definitely lower than the Norgay Montes and the highlands of Krun Macula. In this image, due to the low angle of the Sun, sunlight highlights cliffs that rise up in steps from Sputnik Planum to plateaus in Krun Macula. This makes it clear that here Sputnik Planum is at a lower elevation than the surrounding terrain.



This seems a bit of a puzzle, since at the northern end of Sputnik Planum ice is fairly clearly flowing glacially over the landscape which would imply that Sputnik Planum is higher there. Whereas in the south, between Norgay Montes and Krun Macula, the ice looks like it could be flowing down into Sputnik Planum.

Herobrine, FYI the camera projection of a sphere is never a circle (except if located along the optical axis ie in the middle of the image) but an ellipse. And of course, this is true without the need of any distorsion.
With LORRI this should be almost a circle as the fov is small, but still worth to be aware of that point.

Gnomonic projection deviation from the sphere is 0.015 pixels on the edge of the frame of LORRI.

This is not an argument, because I can say that Krun Macula does not appear to be a highland because it is definitely lower than the Sputnik Planum at its southern end.
We do not know absolute heights neither the one nor the other.
The nature of light is different, because the terrain is different and can not be used to assess systematically slowly changing heights in the transition from Sputnik to Krun against the background of a rapidly changing slopes of relief.
For example, I took a picture of a muffin, which put a little yogurt:

In the photo from side it be clearly seen how the yogurt over a "hilly terrain":


The tile arrangement of dark stripes between the 'convective' cells everywhere directed from the center of Sputnik Planum, so that it seems that all is over was directed from the Sputnik Planum to the Krun Macula.

Friday releases seem to be continuing for LORRI raw images:



http://cosmicdiary.org/mshowalter/2015/09/...campaign=buffer

by Mark Showalter