Pluto System Speculation Options

[HSchirmer]

Sputnik Planum cannot melt into a "sea" because Pluto's atmospheric pressure is far too low to support the liquid phase of N2:


http://astrocampschool.org/wp-content/uplo...ase-diagram.gif

Phase diagram is from a recent (~2014) paper " The surface compositions of Pluto and Charon"
http://www.boulder.swri.edu/~buie/biblio/pub095.pdf

Article doesn't specify pressure, they are dealing with the surface of Pluto, I'd be surprised if they forgot about pressure!
So, N2 on pluto is kinda like H2O on earth, you never find it pure, it usually has something dissolved in it.

But, let's assume surface N2 (actually a mixture) must be solid, or gas.
That means any transient bodies of liquid N2 would "ice over"
not because of cold temperature, but because of lowpressure. Weird eh?

Attached thumbnail(s)

 

[Julius]

I believe they were talking about subsurface liquid nitrogen where temperatures and pressures are higher.

[HSchirmer]

I believe they were talking about subsurface liquid nitrogen where temperatures and pressures are higher.

Perhaps, except the paper is about infrared spectroscopy.
Since they're talking about telescope observations of the spectra Pluto,
I figure they know enough to look at figures for the surface of Pluto...

[HSchirmer]

Sputnik Planum cannot melt into a "sea" because Pluto's atmospheric pressure is far too low to support the liquid phase of N2:

Interesting idea. You need about .1 bar of atmosphere to allow N2 to flow like a liquid on pluto.
Basically, if Pluto had a transient warming event, either procession or perhaps a collision,
the surface temperature would rise to 63 Kelvin, then you'd start melting N2 into atmosphere,
and once you have .1 bar of N2, you could get liquid.

A recent paper calculated that noted the the 10 microbar atmosphere of Pluto would freeze or condense
out into a layer under 1 millimeter thick across Pluto.
Recent numbers suggest Sputnik is about 3 Km deep and appears to be filled with N2 ice.
Some back of the envelope calculations suggest that the amount of N2 ice in Sputnik is just about
the same as the amount of N2 for a thick transient atmosphere where N2 could flow.

Say, current atmosphere now is 10 millionths of a bar, to allow liquid N2 you need .1 bar or 100,000 millionths.
So, you need about 10,000 times more N2.
Based on the 1 millimeter ice gives 10 bar atmosphere, you'd need roughly 10,000 millimeters,
or about 10 meters of N2 ice across pluto vaporized to create a .1 bar atmosphere.

Ok, sputnik appears to be 3,000 meters of N2 ice in one place. Quick size estimate, take 3 great circles
and you get 8 quadrants for a globe, each quadrant is three 90 degree angles draped on the globe.
So, roughly, about 10 sputnik sized areas to cover each quadrant- think of it like stacking balls,
inside the triangular area, bottom row of 4, next row 3, next row 2, top row 1.

And oddly, images of pluto divide pluto into six 60' longitude lines, not 90s, but you get the idea



So, a quadrant is 1/8 or 12.5%, of the surace, at about 10% of a quadrant sputnik covers roughly 1.25% of Pluto.
Call it 1% to keep the math easy. Then 3,000 meters of ice divided into 100 pieces would each be 30 meters thick.

Rather interesting actually - if Pluto does have the occasional runaway green house, (or impact)
it might get to 63 Kelvin with a transient one-tenth bar atmosphere and have liquid N2 for a while.

And it seems like the volume of ice in sputnik is just about what you would see if that entire transient
atmosphere froze out into one polar deposit.

[Gladstoner]

A couple thoughts about liquid nitrogen in/on Sputnik....

As we all have seen, water ice is less dense than liquid H2O, so it floats on the surface. I'm not sure if I'm able to work out all the thermodynamics at this point, but I believe the surface ice serves to insulate the liquid body beneath it. This is why fish can continue to live beneath ponds and lakes in some of the coldest climates.

Solid nitrogen, on the other hand, is denser than its liquid (I'm pretty sure about this). Any N2 ice that forms at the surface would tend to sink to the bottom. As heat convects upward and radiates into space, the whole mass should freeze and remain that way. However, if more liquid is being drawn from another source, or if an internal heat source is melting the deeper nitrogen (as both could be the case with a magma chamber beneath a volcano), then all bets are off.

[Gladstoner]

Question:

Would water ice, as it would exist at the surface and at depth on Pluto, be soluble in liquids (N2, CO, and/or CH4) that could potentially be present in the subsurface? If so, that could go a long way in helping explain some observed surface features.

[HSchirmer]

Question:

Would water ice, as it would exist at the surface and at depth on Pluto, be soluble in liquids (N2, CO, and/or CH4) that could potentially be present in the subsurface? If so, that could go a long way in helping explain some observed surface features.

Well, vice versa for clathrates.
There are some conference papers that consider internal structures with a clathrate layer (N2 or CO or CH4, encased in a soccerball of H2O) along with silicates, interior oceans and ices.

[Gladstoner]

Well, vice versa for clathrates.
There are some conference papers that consider internal structures with a clathrate layer (N2 or CO or CH4, encased in a soccerball of H2O) along with silicates, interior oceans and ices.

Would that also be the case under various other conditions? As it turns out, water ice apparently can dissolve in liquid nitrogen, but can be done only on a small scale under difficult conditions in the laboratory. Imagine how complex the interactions are in the vast scale and intricacies of Pluto's crust and mantle, not to mention all the unknowns (and unknowables). It may be centuries before we have a solid grasp of what makes Pluto tick.

[Juramike]

Liquid nitrogen is a lousy solvent. Especially for polar materials like water ice.

IDK about dissolution of clathrates. Clathrates are extended cage structures of water ice (or other molecules) surrounding a caged molecule in a capped off host-guest interaction. Unclear if one can "dissolve" an intact clathrate. True dissolution would need to break up clathrate structure.

What is largest clathrated structure that could be intimately dissolved by liquid nitrogen?
What is smallest clathrate structure that could still be considered a structurally stable clathrate?

[Gladstoner]

Liquid nitrogen is a lousy solvent. Especially for polar materials like water ice.

Thank you. That would put constraints on possible processes.

[alan]

Would mixing in carbon monoxide with the nitrogen affect the solubility of water?

[HSchirmer]

Would mixing in carbon monoxide with the nitrogen affect the solubility of water?

Probably.

Actually, in real life, all the volatile ices are mixtures, N2 and CH4 and CO all appear to be miscible in each other.

Carbon monoxide, CO, is an interesting suggestion for modifying H2O solubility.
Both are polar, and both contain oxygen, so the molecules are at least somewhat comparable in size.

So, while oil and water don't mix, adding soap allows them to.
Similarly, N2 and water might not mix well, (still not sure about measurements at Pluto temp & pressure)
but adding carbon monoxide might allow more miscibility.

[Gladstoner]

The surface age of Sputnik Planum, Pluto, must be less than 10 million years

Thanks for the link. Interesting stuff.

A few more questions to add to the pile....

- Couldn't sublimation of nitrogen (et al.) at the surface also erase features such as craters?
- If so, would it occur so slowly that its effects would be superceded by other processes (i.e. one or more of the three mentioned in the article)?
- If the sublimation did occur fairly rapidly, how then could the age of the surface be determined.... or even defined?
- Could meteor impacts influence the arrangement of the (eventual) patterns of the surface pits? If so, older impacts potentially could be identified.

Come to think of it.... It is fascinating to think about the effects of impacts into nitrogen ice. I'm not sure that I can accurately imagine such a thing....

[Bill Harris]

...Unclear if one can "dissolve" an intact clathrate. True dissolution would need to break up clathrate structure.

What is largest clathrated structure that could be intimately dissolved by liquid nitrogen?
What is smallest clathrate structure that could still be considered a structurally stable clathrate?

That has occurred to me, too. A clathrate couldn't dissolve and still be a clathrate. But could it weather (physically break down) into a minimum clathrate "cell" or structure? I tend to think of clathrates as being akin to silicates at these temperatures, but that is not a strict analogy since the SiO4 and H2O bonds are way different. What would clathrate nanoparticles behave like?

'Tis truly an alien world.

--Bill

[Gladstoner]

The nut-cluster'-like texture of the rolling hills around Wright Mons is interesting, particularly in the lower left:



This knobby texture appears to be present in various forms in many other areas on Pluto, including in the ancient terrain of Krun Macula (center of image):



And in the linear, fingerprint-like texture in areas north of Sputnik:



And the Zebra herd mountains:



Joint patterns in the water-ice crust come to mind, but it may be more to it than that.

FWIW, it could indicate that Wright Mons itself is made up of water ice.