Pluto Surface Observations 1: NH Post-Encounter Phase, 1 Aug 2015- 10 Oct 2015 |
Pluto Surface Observations 1: NH Post-Encounter Phase, 1 Aug 2015- 10 Oct 2015 |
Aug 1 2015, 05:53 PM
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#1
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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
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Aug 10 2015, 11:38 AM
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#2
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Member Group: Members Posts: 137 Joined: 16-June 15 Member No.: 7507 |
QUOTE If liquid phases of N2 are stable a few meters down That shouldn't be possible. N2 requires a minimum of around 15-20 meters of ice at Pluto's pressure and gravity at an optimal temperature. Eutectics may have a significant impact on the required temperature range, but they're unlikely to lower the pressure requirements, esp. since nitrogen has much lower pressure requirements than CO, Ne, etc. I wouldn't be surprised if there are actual liquids there rather than just flowing solids (though the boundary between liquids and solids is kind of fuzzy in this context). But if so they're going to be a lot deeper than just a couple meters. It'd also mean that temperatures would either have to be a bit warmer than Pluto's average solar equilibrium temperature, or that eutectics would need to lower the triple point temperature. Neither are unrealistic possibilities, but there's no guarantees either - and the high albedo of Tombaugh works against it. I really want to see closeups of the "crack" patterning on Sputnik. I'm really curious as to whether they'll appear to be something filled in by liquid. Too bad there's no radar data to be able to get an idea of surface texture... I'd love to know if there's any "cryolava pillowing" going on if liquids ever reach the surface. Then again, nitrogen may not be able to form a sturdy enough shell to form pillows - we've all seen the videos of how it behaves when it's rapidly evaporatively cooled. |
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Aug 10 2015, 02:38 PM
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#3
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Member Group: Members Posts: 684 Joined: 24-July 15 Member No.: 7619 |
QUOTE If liquid phases of N2 are stable a few meters down That shouldn't be possible. N2 requires a minimum of around 15-20 meters of ice at Pluto's pressure and gravity at an optimal temperature. Eutectics may have a significant impact on the required temperature range, but they're unlikely to lower the pressure requirements, esp. since nitrogen has much lower pressure requirements than CO, Ne, etc. I wouldn't be surprised if there are actual liquids there rather than just flowing solids (though the boundary between liquids and solids is kind of fuzzy in this context). But if so they're going to be a lot deeper than just a couple meters. Correct, it's a few tens of meters, not just a few meters. The Nitrogen ice making up the majority of Pluto's surface, has two allotropes, one with a hexagonal type crystal structure, the other has a cubic structure, the same as diamond. This second form only forms at high pressure. It is reasonable to propose that the rim of the crater and the basin itself, is composed of this "harder" form of Nitrogen ice and is covered in the "softer", "normal" Nitrogen and Carbon Monoxide ice. This softer ice does not have the mechanical strength to sustain the height of the crater rim and so has "slumped" in a more "plastic" flow, over the more solid layer below. One early suggestion was that with a-phase and b-phase ice, you would get "phase change fronts" moving across the surface and into the subsurface in response to changes in heat and sunlight. I suspect that a phase change would result in a volume change, that stress could be an effective mechanism to erode the surface There's a later paper that estimates where each form of N2 ice is stable during each orbit. http://www.lpl.arizona.edu/~yelle/eprints/Stansberry99a.pdf Stansberry & Yelle, “Emissivity and the Fate of Pluto's Atmosphere,” Icarus 141: 299-306, 1999 Interesting that their calculations predict a "phase cliff" about 20 years past perihelion, (roughly now) where the southern hemisphere abruptly switches from B-ice being stable to A-ice being stable. |
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Aug 13 2015, 03:30 PM
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#4
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Member Group: Members Posts: 153 Joined: 20-December 14 From: Eastbourne, UK Member No.: 7372 |
There's a later paper that estimates where each form of N2 ice is stable during each orbit. http://www.lpl.arizona.edu/~yelle/eprints/Stansberry99a.pdf Stansberry & Yelle, “Emissivity and the Fate of Pluto's Atmosphere,” Icarus 141: 299-306, 1999 Very illuminating paper that. The amount of exposed alpha N2 ice would seem to have an effect on the equilibrium of the whole atmosphere. Most interesting is that the two phases can exist as a mixture. This suggests to me, Nitrogen frost build up to levels above a few metres results in a gradual phase transition, first to the denser, alpha ice allotrope and at even greater depths there is the possibility of liquid Nitrogen forming, perhaps in cracks and voids in the ice. A process similar to ice crystals building a glacier. This "liquid aquifer" might one would think, be trapped below the alpha phase Nitrogen ice, similar to oil and natural gas underground on Earth capped by an impervious rock layer, allowing pressure build up. All sorts of interesting possibilities arise if this is the case, especially if some heat is still emanating from the core below, or the "aquifer" is penetrated by an impact. |
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Aug 14 2015, 04:41 PM
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#5
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Member Group: Members Posts: 684 Joined: 24-July 15 Member No.: 7619 |
Very illuminating paper that. The amount of exposed alpha N2 ice would seem to have an effect on the equilibrium of the whole atmosphere. Most interesting is that the two phases can exist as a mixture. ... Well, thats the amazing thing, if Pluto's surface N2 is a solid solution, e.g. it changes from alpha to beta N2-ice and back again, raises some weird possibilities. Phase transitions make great buffering solutions because of latent heat, literally "hidden heat". That is, you can measure the temperature of the system with precision, but you won't know how much energy is stored in the system. Or to paraphrase my old chemistry professor, "burn your fingerprints off pyrex test tubes look like normal pyrex test tubes"... Point is, a feature that is N2 ice at, say 40 kelvin, you won't know whether it's thin coat of frost on frigid H20 mountain, or the last coat of frost on a N2 mud-pot geyster that is about to blow sky high. |
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Aug 15 2015, 02:08 PM
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Member Group: Members Posts: 153 Joined: 20-December 14 From: Eastbourne, UK Member No.: 7372 |
The video below shows liquid Nitrogen freezes initially into an amorphous, "glass" like solid, before assuming the hexagonal Beta phase. There is a possibility, given the right temperature and pressure, of all three phases existing on the surface of Pluto should the postulated liquid Nitrogen from below, flow onto the surface in large volumes.
https://www.youtube.com/watch?v=c0rK2bLTimQ The differing optical properties and grain sizes of crystals of Alpha and Beta N2 ice in a mixture are going to be relevant to its visible appearance. Phil suggested earlier grain sizes and transparency as a possible explanation for the appearance of the Northern Tombaugh "glaciers". Altitude of the terrain is important in determining the ratios of the two phases, which tends to suggest to me that this idea combined with "plastic" flow, possibly of amorphous ice, is along the right lines. Another issue is sintering of surface ices and its effect on its physical and visual properties. On top of all that is contamination of the Nitrogen ice with other molecules. More data definitely required. |
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Aug 16 2015, 12:00 PM
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#7
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Member Group: Members Posts: 101 Joined: 3-May 12 From: Massachusetts, USA Member No.: 6392 |
Fascinating video, thank you for sharing it.
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