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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Merciless Robot Group: Admin Posts: 8785 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
This topic will contain images & discussion of same as they arrive during the extended download period. Similar threads will be opened in coming months as required as acquired data & discussion proceeds.
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Aug 10 2015, 11:38 AM
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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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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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