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Pluto Atmospheric Observations: NH Post-Encounter Phase, 1 Aug 2015- TBD
remcook
post Aug 12 2015, 06:05 PM
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About the phase functions, here ( http://inspirehep.net/record/1127473/plots , first plot) is a plot of the size of the forward-scattering peak of the phase function as a function of wavelength for different solar system particles. Notice the log scale. Also, the Titan book chapter nicely shows how very much forward-scattering Titan particles are. The forward-scattering peak is much more intense than in the polar plot by Gennady. But we don't know whether that holds for Pluto of course.
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scalbers
post Aug 12 2015, 06:11 PM
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Offhand, the phase function peak is more typically ranging from 20-1000 for various solar system hazes (including Earth). This agrees with the figure in 'remcook's link. The larger the particles, the larger the peak. So Gennady's plot value of 6 might indeed benefit from being increased. If we consider exactly where the sun is behind the disk of Pluto, then the asymmetry of the annular glow may help a bit in determining the phase function if shadowing effects of Pluto on its atmosphere are also considered. LORRI's field of view though is a bit small though for the scattering angle to vary much over the image.


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JRehling
post Aug 12 2015, 06:40 PM
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Meteors may appear over Earth at altitudes where the pressure is less than the maximum surface pressure on Pluto, which suggests that visible meteors could be possible (were there anyone there to see them). However, recall that the velocity of meteors running into Pluto should be much less than the velocity of meteors hitting Earth's upper atmosphere. However: Water ice wouldn't remain ice when it was hot enough to glow, and would soon be a puff of vapor.

So, a visible meteor on Pluto would require an anomalously high velocity, and for the speck to be silicate rather than ice. I'll bet it's happened, but rarely.
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fredk
post Aug 12 2015, 07:41 PM
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QUOTE (scalbers @ Aug 12 2015, 07:11 PM) *
If we consider exactly where the sun is behind the disk of Pluto
If you mean the released LORRI post-encounter images, the sun is not behind Pluto. NH was 360 000 km from Pluto in the closer post-encounter frames, which is much farther than the Pluto-sun occultation distance (very roughly 50 000 km). Conversely, LORRI would only see a small fraction of Pluto during the occultation.

The variation in brightness we see around the limb in those shots is mainly due to the presence of a very slim sunlit crescent, though presumably the haze is somewhat in shadow on the opposite limb.

Edit: this assumes you meant "occulted by Pluto" when you said "behind Pluto".
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nprev
post Aug 13 2015, 04:01 AM
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Copied post from stevesilva over on the 'interesting/boring objects' thread that is relevant here:

QUOTE
New press release today about accounting for Pluto's rate of Nitrogen loss, and how endogenic processes might be the source for it...
http://pluto.jhuapl.edu/News-Center/News-A...p?page=20150812
and this...
https://blogs.nasa.gov/pluto/2015/08/10/atm...lutos-nitrogen/


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Gennady Ionov
post Aug 13 2015, 04:27 AM
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Thank you, Explorer, Bill!
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Explorer1
post Aug 13 2015, 04:44 AM
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They do in the main post; I've copied the link locations:

http://pluto.jhuapl.edu/News-Center/News-A...p?page=20150812

https://blogs.nasa.gov/pluto/2015/08/10/atm...lutos-nitrogen/
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nprev
post Aug 13 2015, 05:05 AM
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Whups! Sorry. Thanks, Explorer. smile.gif


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Bill Harris
post Aug 13 2015, 08:11 AM
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Why not _fix_ the bad links in the earlier post? Leaving them dead, and finding the corrections two posts later, is noisy.

And possibly including a direct link to the PDF might be spiffy:
http://iopscience.iop.org/2041-8205/808/2/...5_808_2_L50.pdf

wink.gif


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Sherbert
post Aug 13 2015, 02:07 PM
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QUOTE (JRehling @ Aug 12 2015, 07:40 PM) *
Meteors may appear over Earth at altitudes where the pressure is less than the maximum surface pressure on Pluto, which suggests that visible meteors could be possible (were there anyone there to see them). However, recall that the velocity of meteors running into Pluto should be much less than the velocity of meteors hitting Earth's upper atmosphere.

The evidence from military satellites is that numerous bolide airbursts, many probably from icy comet debris, occur tens of kilometres high in the atmosphere of Earth, where densities are comparable to those in Pluto's atmosphere. Some of these "explosions" are in the megatons of TNT range and at first were suspected as being atomic bombs. The well known Tunguska Event is thought to be the result of such an airburst a few kilometres above the surface. This paper and article by Gasperini et al on the possibility of the impactor being a comet and the morphology of a possible impact crater, suggests there are some applicable numerical models out there which could be used.

http://onlinelibrary.wiley.com/store/10.11...da53l2w8da6b86d

http://www.geotimes.org/feb08/article.html?id=nn_crater.html

The key here, as you suggest, is the inertia of the impactor. A sufficiently large icy object from the Oort Cloud travelling at interplanetary velocities impacting Pluto's atmosphere could be postulated to result in an atmospheric "airburst", one which, intuitively, would be a lot closer to the surface of Pluto given the very low atmospheric density.

If the Tombaugh Regio is the result of such a cometary impact, should we be looking for evidence of an accompanying "airburst"? This image by G.I. suggests there may be some visible along the South Western side of Tombaugh, (top right in the image). Together with the "snow cone" shape of the Western half of Tombaugh Regio, the depression at the base of the "cone" and the flattened terrain surrounding it, it seems worth further investigation when more topographic data is available.

http://www.unmannedspaceflight.com/index.p...st&id=37400
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Bill Harris
post Aug 13 2015, 02:37 PM
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At Earth solar distances, we are not going to find icy debris particles. Fluffy refractory chunks are likely.

And watch out making too many Earth-analogies. Although cosmic uniformitarianism is a valid principle, Pluto is an strange alien world.

--Bill



AND, quite welcome Gennady!


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Gennady Ionov
post Aug 13 2015, 03:30 PM
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QUOTE (Sherbert @ Aug 13 2015, 07:07 PM) *
This image by G.I. suggests there may be some visible along the South Western side of Tombaugh, (top right in the image). Together with the "snow cone" shape of the Western half of Tombaugh Regio, the depression at the base of the "cone" and the flattened terrain surrounding it, it seems worth further investigation when more topographic data is available.

Hmm, unexpected use my picture :-)
As for the Tombaugh Regio and of the equatorial darkening I have my own hypothesis, which appeared in early July. Too crazy to her voice.
I'm afraid that the moderator would not welcome her appearance here. At least I have encountered this in Russian forum.
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scalbers
post Aug 13 2015, 04:37 PM
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QUOTE (fredk @ Aug 12 2015, 07:41 PM) *
The variation in brightness we see around the limb in those shots is mainly due to the presence of a very slim sunlit crescent, though presumably the haze is somewhat in shadow on the opposite limb.

Thanks for pointing this out. The blue enhancement may be less then due to the difference in the sharpness of the phase function peaks related to the size parameter. What is the scattering angle? We still have the Angstrom exponent caused blueness as a factor.

Surface reflectance and roughness properties then become of interest in determining how bright the crescent would be.


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Bjorn Jonsson
post Aug 13 2015, 05:39 PM
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Here is an animation I did of the New Horizons flyby that includes atmospheric effects:

https://vimeo.com/136223988

I changed the atmospheric model to make the haze/aerosols gray. I'm using Mie scattering only and assuming that there is no wavelength dependence. The particles are gray which could easily be an incorrect assumption. The phase function I used is Cornette's improved version of the Henyey-Greenstein function. The parameters I used result in values ranging from 0.1 (phase angle 0) to 27.2 (phase angle 180):

Attached Image


The phase function is simply a guess and it works fairly well for terrestrial scenes but parameters almost certainly have to be adjusted once we see images of the haze/aerosols at a greater range of phase angles.

The scale height of Pluto's atmosphere is ~60 km according to pre-NH measurements. I'm using a scale height of 55 km for the aerosols which may or may not be correct. I tested other values; 30 km was visually different from the NH high-phase images and it was also not possible to increase the values to much more than 60 km without getting bad results.
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Sherbert
post Aug 13 2015, 05:47 PM
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QUOTE (Bill Harris @ Aug 13 2015, 03:37 PM) *
And watch out making too many Earth-analogies. Although cosmic uniformitarianism is a valid principle, Pluto is an strange alien world.

Quite true Bill and I hesitate to hypothesise further without better evidence or access to the required models. I could be adding 2 and 2 to get 5.

I would add that chunks of icy material do cross the orbit of Earth on a regular basis in the form of comets and their debris, some detectable and some not.
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