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Pluto Surface Observations 1: NH Post-Encounter Phase, 1 Aug 2015- 10 Oct 2015
Bjorn Jonsson
post Aug 7 2015, 11:41 PM
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QUOTE (alan @ Aug 6 2015, 09:06 PM) *
I believe these are the MVIC and LORRI Charonshine images listed in the New Horizon's Full Activity List

QUOTE
July 14 08:08:13 EDT New Horizons is taking an image of Pluto with MVIC from 20323.226 km away at est. resolution 0.40 km/pix.

July 14 21:47:42 EDT New Horizons is taking 180 images of Pluto with LORRI 4x4 from 692198.32 km away at est. resolution 14 km/pix.



Assuming that the information above is correct, the illumination for the two observations listed above would be like this:

Attached Image

Attached Image


The upper image (the one simulating the MVIC geometry) has a FOV of 10 degrees and the lower one a FOV of 0.2907 degrees (the LORRI FOV).

I made no attempts to make the brightness of the Charonshine areas correct relative to the bright sunlit limb. These test renders are primarily intended to approximate which areas are in Charonshine. Charon is modeled as a point source but that doesn't make a big difference (in reality the illuminated area should be slightly bigger).
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Gennady Ionov
post Aug 8 2015, 09:29 AM
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With the use of map
http://www.unmannedspaceflight.com/uploads...19373_thumb.png
I simulate the frame
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x632_sci_3.jpg
and got a picture
Attached Image
Attached Image
Attached Image

(To comparision the original frame are placed in the last right and difference between the original and the simulated image can be seen on an middle picture)
There is some distortion of the image is apparently due to the different definitions of the rotation axis and the longitude, as well as slight map distortion.

QUOTE (Phil Stooke @ Aug 8 2015, 01:42 AM) *
As for the range of longitudes, as the system rotates the illuminated night half will sometimes be better placed for viewing, sometimes less so. Light bleed from the sunlit crescent will be a problem, so when the Charonshine region is adjacent to the sunlit crescent we should have better viewing geometry but worse light pollution. When it's opposite the sunlit crescent it will be foreshortened but less contaminated. So a lot depends on the timing of imaging. I would like to see some simulations of this.


Also I plan to simulate other LORRI and MVIC frames (include Charonshine frames)...
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Bjorn Jonsson
post Aug 8 2015, 12:17 PM
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I have been experimenting with generating DEMs of Pluto from stereo imagery, mainly to see if there are any large scale elevation differences (e.g. from subtle impact basins). The images available so far aren't exactly optimal for this and also my stereo match software is very sensitive to compression artifacts.

So far I have tried two stereo pairs:
lor_0299174713_0x632_sci_5.jpg and lor_0299148167_0x632_sci_3.jpg
lor_0299175145_0x632_sci_7.jpg and lor_0299148167_0x632_sci_3.jpg (again)

These pairs are far fram optimal since the resolution of lor_0299148167_0x632_sci_3.jpg isn't high and the resolution difference between the images is large (differs by a factor of ~6). Sputnik Planum is also almost featureless in the lower-res image, making it difficult to find matching features. The resulting DEM is noisy and too ugly to post here but at least there is one possible result: Sputnik Planum is *probably* not a depression, its elevation is *probably* comparable to the elevation of the surrounding, dark terrain (if Sputnik Planum is despite this really a depression it would probably be a very gentle depression, much more so than big craters and basins on e.g. Rhea). But I want to emphasize the word "probably" in everything here - the DEM is noisy and of low quality.

I also experimented with the lor_0299148167_0x632_sci_3.jpg / lor_0299124574_0x632_sci_1.jpg pair but without any useful results. The resolution is too low and compression artifacts mess things up.

By the way, one of the most interesting features I noticed when I was doing the DEM work was this in image lor_0299174713_0x632_sci_5.jpg, slightly sharpened here:

Attached Image


Here the stuff in Sputnik Planum has apparently been flowing into a crater. This reminds me of terrestrial glaciers - seeing higher-res images of Sputnik Planum's edge is going to be really interesting.

Of course the vast majority of the really interesting (i.e. hi-res) images are still aboard the spacecraft. As interesting and exciting as everything has been so far, the real fun really doesn't start until September when downlinking of the imaging data starts.


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HSchirmer
post Aug 8 2015, 07:04 PM
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QUOTE (Bjorn Jonsson @ Aug 8 2015, 12:17 PM) *
...
Here the stuff in Sputnik Planum has apparently been flowing into a crater. This reminds me of terrestrial glaciers - seeing higher-res images of Sputnik Planum's edge is going to be really interesting.


Can't wait to see the topgraphy!

Does it appear to anybody else that the hill-ice field boundary appears like the N2 ice is dissolving the rough terrain, not flowing over it?
E.g., the dark swirls look like chocolate terrain dissolving into the milky N2 ices?

The flow patters seem more like dark material being drawn into the lighter colored ice field, not like white ice advancing over a dark terrain.
If liquid phases of N2 are stable a few meters down, you'd have a glacier that "skated" on the liquid layer and also dissolved the surrounding terrain.

There should be some very interesting "geology" err, "iceology" here, solid solutions, eutectic solutions might create icy analogs of sedimentary or igneous rocks.
Grains of different ices held together in a matrix of another ice or mixture of ice.
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Phil Stooke
post Aug 8 2015, 07:19 PM
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The dark swirls may be due to grain size changes, or areas of transparent ice. When we are looking at nitrogen ice, carbon monoxide ice and so on, it's very difficult to know what would dissolve in what, so I prefer a physical explanation at the moment.

Phil


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nprev
post Aug 8 2015, 08:11 PM
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Agreed, Phil. These wide-view images don't provide nearly enough detail to understand what's going on at the process/mechanism level yet. Hopefully there will be clues worthy of hypothesis formation found in the most detailed pics yet to come.


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Bjorn Jonsson
post Aug 8 2015, 09:20 PM
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Speaking of ices, glaciers, flow patterns etc., a lot of examples of how terrestrial glaciers can appear can be seen in a big mosaic I did a few years ago of southern Greenland from Landsat 7 images: http://www.planetary.org/blogs/guest-blogs...nd-jonsson.html

There appear to be some superficial similarities but it must be kept in mind that the resolution of the Pluto images is much lower (the resolution of the Landsat mosaic is ~30 m/pixel).
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ngunn
post Aug 8 2015, 09:25 PM
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I'm not yet convinced there is flowing ice here. Light and dark dust being wafted around in the thin air seems more likely.
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Bjorn Jonsson
post Aug 8 2015, 09:32 PM
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I'm not either - as I mentioned above, the resolution of the Pluto images really isn't very high yet. The highest-res images will be really interesting, plus surface composition measurements (LEISA data).
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HSchirmer
post Aug 9 2015, 04:32 PM
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QUOTE (Bjorn Jonsson @ Aug 8 2015, 10:32 PM) *
I'm not either - as I mentioned above, the resolution of the Pluto images really isn't very high yet. The highest-res images will be really interesting, plus surface composition measurements (LEISA data).


Has anybody done a montage of similar scale / resolution images of ice features?
Say, Tombaugh with 20 mile size bar, then Enceledaus, then Europa, then Martian chaos terrain, then Earth arctic?

Idea being, even with physical chemistry that is fundamentally different, Titan has features which are recognizable,
presumably because the materials are different, but the math and the patterns remain the same.
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Nafnlaus
post Aug 10 2015, 11:38 AM
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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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Sherbert
post Aug 10 2015, 01:38 PM
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Since the older surface and the "glaciers" are suggested to be both made of mainly N2 ice, might it not be better to think in terms of "lava" flow rather than "Glacial" flow. Glacial flow requires lubrication, which could be possible under the main icecap, but towards the edges the lubrication would freeze and the "glacier" analogue looks less applicable.

The Northern part of Tombaugh Regio seems to be a large impact basin, one that has been largely filled in with Carbon Monoxide ice. 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 might guess the "diamond" form of Nitrogen ice might be close to transparent too. Not sure if the Ralph or Alice data could differentiate between the two forms of Nitrogen ice, it could be very informative if they can.

The shock wave travelling through the surrounding ice could also create "ridges" of harder Nitrogen ice. G.I.'s image suggests this possibility in the area to the North West of Tombaugh (5 O'Clock in the image).
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HSchirmer
post Aug 10 2015, 02:38 PM
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QUOTE (Nafnlaus @ Aug 10 2015, 12:38 PM) *
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.

QUOTE (Sherbert @ Aug 10 2015, 02:38 PM) *
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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Gennady Ionov
post Aug 10 2015, 07:00 PM
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With the use of metadata of LORRI frames I clarify trajectory of New Horizons (error is about 0.000002 on distancies to Pluto at snapshots momens). After that it made possible to simulate all frames with subpixel accuracy. Here for example, two of these frames:
Attached Image
Attached Image

As a bonus Pluto radius was determined: R=240.89 km * u, where 'u' is LORRI pixel size in microradians.
If we assume that the under-Charon avarage point has longitude 0, then the map of Pluto (for example http://www.unmannedspaceflight.com/index.p...t&id=37374) is offset by 1.6 to the east. So I had to make such correction to map, that the image consistent with LORRI frames.
Nevertheless, clear to see that there are still quite a strong distortion in the map.
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Bjorn Jonsson
post Aug 10 2015, 07:25 PM
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QUOTE (Gennady Ionov @ Aug 10 2015, 07:00 PM) *
With the use of metadata of LORRI frames I clarify trajectory of New Horizons (error is about 0.000002 on the current distance to Pluto). After that it made possible to simulate all frames with subpixel accuracy. Here for example, one of these frames:

As a bonus Pluto radius was determined: R=240.89 km * u, where 'u' is LORRI pixel size in microradians.


This translates to 1193.6 km, consistent with the 1185 +/- km measured by the NH team a day before the flyby (interestingly, I got a value of 1194 km km back then).

Regarding NH's trajectory, if I remember correctly the flyby didn't occur at exactly the planned time (off by some seconds but well within the required accuracy) and this makes it more tricky to use the metadata to accurately determine the viewing geometry (especially in the hi-res images) until an updated trajectory (SPICE kernels) becomes avvailable.



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