Pluto Surface Observations 1: NH Post-Encounter Phase, 1 Aug 2015- 10 Oct 2015 Options

[Nafnlaus]

What I was was trying to copy was a phase diagram for nitrogen showing the triple point at just above 0.1 atmospheres. That seems a remarkably high pressure for the surface of Pluto at any epoch. Maybe the liquid nitrogen flows ocurred subsurface and the evidence was exhumed later.

Correct. I did the calculations a while back - on Pluto as it is today it would take a layer of nitrogen something like 18 meters thick (assuming no pore space) to create the requisite pressure to allow liquids to exist, and the temperature would have to be relatively high by Pluto standards (although the albedo of nitrogen ice would tend to create just the opposite, a cold spot). But between tholin dustings, localized internal heating from a variety of mechanisms, and/or eutectics, it could be possible today. In the past, who knows - clearly the NH team sees evidence of past fluid erosion on the surface, and that's pretty fascinating. It's not hard to picture mechanisms that would temporarily dump massive amounts of nitrogen into the atmosphere (impacts, volcanism, "rapid" crustal overturn, etc) and create the potential for major flash floods.

As for the concept that Sputnik today could be underlain by liquid, note that pore space would be required to loft solid nitrogen atop liquid nitrogen on Pluto, as solid is significantly denser than liquid. But that's probably not a problem, vacuum-frozen nitrogen is very "fluffy" - so long as it didn't wet fully into slush, it should float. Mind you, I doubt that such high levels of porespace would persist over geologically long timeperiods, so periodic subduction of older, denser "crust" could well be a "thing". On the other hand, if it did prove to be prone to wetting fully into slush, leaving insufficient pore space to loft it, you'd have constant overturn until the liquid froze all the way through. I've been unable to locate any research on exactly what scenario is most likely in Pluto conditions. I seem to recall a study on Titan arguing that fluffy methane and ethane ices could persist for relatively long periods on the surfaces of its seas, although that's clearly a different scenario.

All of this said, you don't really actually need liquids to have flows when dealing with nitrogen, solid nitrogen at these temperatures has rather little structural integrity and is quite prone to flowing on its own. Hence the NH's team's original hypothesis that Sputnik's curious appearance is due to solid state convection. Now that they seem to be considering the possibility that Sputnik is a frozen cap atop flowing liquids, this would seem to suggest that the boundaries of the "convection cells" are crust subduction zones. Either way, I can't wait to see more details about what they have to say!

[MarkG]

Well, I guess calling it a "mare" is not so farfetched after all....

So, chemically, is there anything we are likely to see that that dissolves in liquid nitrogen? Is there a substance that could affect the phase diagram, or the density? Would we possibly be looking at the Plutonian analog of "salinity flows"?

[Gladstoner]

So, chemically, is there anything we are likely to see that that dissolves in liquid nitrogen?

The terrain near Krun Macula resembles karst -- to my eyes, at least. If there are similar proceseses within Pluto, where subterranean fluids dissolve bedrock (bed-ice), that would certainly complicate the interpretation of surface features.

[Charles Astro]

Another look at what may be Pluto's biggest beached iceberg (or 'crust-berg') in Bare Montes.

The context of Bare Montes. A larger version of this image.

The form of the 130 km wide island just off shore in Sputnik Planum is difficult to interpret because its surface texture is near the limit of the resolution of the available images and since it is so unfamiliar we have little context for it. Several of the sections of parallel lines are at small angles to each other, yet if they are something like dunes on top of a mesa they should be parallel. In other places the parallel lines follow curves like contour lines. These things suggest that the parallel lines might be due to layering within the structure. With this in mind, reinterpreting the shape does lead to a self-consistent picture which is somewhat more complex than the simple mesa that I suggested in my earlier post (#413 on Sep 24).


The shore-ward half of Bare Montes may have a complex structure of cliffs and canyons. A larger version of this image is also available here.

[ZLD]

The 'dune-like' field is certainly not as tall as your outlining would suggest. That would be enormously high. Take note of the nearby crater to the lower region of that image. The shadow should be just as strong on an uplifted segment of terrain as it is off the rim of a sunken crater. Edit: not a shadow. Still, this structure would be completely unstable and extremely unlikely at such heights.

[Nafnlaus]

Well, I guess calling it a "mare" is not so farfetched after all....

So, chemically, is there anything we are likely to see that that dissolves in liquid nitrogen? Is there a substance that could affect the phase diagram, or the density? Would we possibly be looking at the Plutonian analog of "salinity flows"?

In the past I've run into papers describing N2 eutectics with methane, carbon monoxide, and neon - the former two whose spectrums have been seen with the nitrogen in Sputnik (AFAIK neon hasn't been detected on Pluto). Neon significantly lowers the triple point temperature (as its triple point is lower), while one of the former two (I forget which one) allows one to have liquids at a mildly colder than pure N2 when a small amount is mixed in (although the triple point is still rather warm by Pluto standards). I'm sure if you google you'll find the papers yourself.

Really, though, it wouldn't take too much internal heat at all to boost the temperature 10-20 degrees; you've got an insulating ice cap, and radiative heat loss is proportional to T^4, so it drops to extremely low rates at cryogenic temperatures. If the heat is there then there should be liquids dozens of meters under the surface at Sputnik - you have your heat, you have your pressure... it's what should happen. But whether said heat is actually there and whether there actually are liquids, I'm not going to speculate.

[ZLD]

Exposed water ice related to brightest red patches on Pluto.



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Here's a modification I made to the crop_p_color2 image a while back that I haven't posted yet.



This expands the separation of colors more to show more contrast between areas. The brightest orange areas are apparently related to exposed water ice. Just some light speculation but possibly if there is any active tectonics going on here and the water rock-ice has previously been mixed with organics in a more active past, insolation could still interact with them creating the tholins.

A few strange features of this bright orange/red water rock ice seem to reside exposed in the northern area. I can't even begin to imagine how those sort of features could come to exist if they are made of water ices.

[alan]

Well that's a change from their repeated discoveries of water on Mars.

ETA: on a more serious note, some of the brighter red areas are on slopes like the fracture and some of the 'mountains on the boundaries of Sputnik Planum so the ice could be exposed by landslides. But what about the flatter areas?

Then there is the chaos terrain at SP's NW corner (not covered in the latest release) where the brighter red fills most of the area between the large chunks, if this is exposed water ice, could that be a sign that the pieces have shifted location in the recent geological past?

[Julius]

It would look like the bedrock on pluto is made up of water ice and mostly represents the heavily cratered 'old' terrain. The newer areas are covered with other ices methane, carbon monoxide and nitrogen presumably over an underlying water ice bedrock.

[Nafnlaus]

It would look like the bedrock on pluto is made up of water ice and mostly represents the heavily cratered 'old' terrain. The newer areas are covered with other ices methane, carbon monoxide and nitrogen presumably over an underlying water ice bedrock.

My take exactly. Also, we don't know whether the red is "embedded in" the ice or just a thin dusting over it that's not otherwise messing with its spectral signature. Either way, I totally agree that it makes sense that we simply see water ice on the crust wherever other ices haven't condensed atop it.

[Req]

My take exactly. Also, we don't know whether the red is "embedded in" the ice or just a thin dusting over it that's not otherwise messing with its spectral signature. Either way, I totally agree that it makes sense that we simply see water ice on the crust wherever other ices haven't condensed atop it.

Even in a perfect vacuum with no type of volatile transport at all, wouldn't one expect exposed water ice to sublimate away until a sufficient insulating layer of it's impurities to prevent sublimation covers the surface?

[ZLD]

In a simple correlation using the average color of the announced exposed ice, I've color-replaced all similarly colored areas on Pluto in the image below:



This definitely couldn't be considered conclusive. The chaos terrain is especially puzzling though unless Pluto has or had much more internal energy than would ever be expected. The area the north, I would chalk up to being erroneous due to lighting conditions and the strong stretch of the color layer but who knows...

[alan]

If there is a correlation then the water ice is exposed in a band at ~30 degrees latitude but primarily west of Sputnik Planum. Recently exposed by the sublimation of nitrogen as the seasons change perhaps. The frost may permeate the soil and disturb it enough when it vaporizes to leave patches of exposed water ice mixed with the tholin dust.

[Julius]

If there is a correlation then the water ice is exposed in a band at ~30 degrees latitude but primarily west of Sputnik Planum. Recently exposed by the sublimation of nitrogen as the seasons change perhaps. The frost may permeate the soil and disturb it enough when it vaporizes to leave patches of exposed water ice mixed with the tholin dust.

This would mean that what we see on pluto is simply ice sublimation and deposition together with tholin dust modification of the surface. What about the role of tectonic forces if any are present?

[alan]

ZLD: I see an shift in color that follows a straight line, a bug somewhere?