Pluto Atmospheric Observations: NH Post-Encounter Phase, 1 Aug 2015- TBD |
Pluto Atmospheric Observations: NH Post-Encounter Phase, 1 Aug 2015- TBD |
Aug 12 2015, 06:05 PM
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#31
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Rover Driver Group: Members Posts: 1015 Joined: 4-March 04 Member No.: 47 |
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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Aug 12 2015, 06:11 PM
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#32
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Senior Member Group: Members Posts: 1670 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
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.
-------------------- Steve [ my home page and planetary maps page ]
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Aug 12 2015, 06:40 PM
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#33
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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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Aug 12 2015, 07:41 PM
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#34
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Senior Member Group: Members Posts: 4260 Joined: 17-January 05 Member No.: 152 |
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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Aug 13 2015, 04:01 AM
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#35
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Merciless Robot Group: Admin Posts: 8789 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
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/ -------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Aug 13 2015, 04:27 AM
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#36
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Junior Member Group: Members Posts: 82 Joined: 13-July 15 Member No.: 7579 |
Thank you, Explorer, Bill!
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Aug 13 2015, 04:44 AM
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#37
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Senior Member Group: Members Posts: 2113 Joined: 13-February 10 From: Ontario Member No.: 5221 |
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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Aug 13 2015, 05:05 AM
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#38
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Merciless Robot Group: Admin Posts: 8789 Joined: 8-December 05 From: Los Angeles Member No.: 602 |
Whups! Sorry. Thanks, Explorer.
-------------------- A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Aug 13 2015, 08:11 AM
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#39
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Senior Member Group: Members Posts: 3009 Joined: 30-October 04 Member No.: 105 |
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 -------------------- |
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Aug 13 2015, 02:07 PM
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#40
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Member Group: Members Posts: 153 Joined: 20-December 14 From: Eastbourne, UK Member No.: 7372 |
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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Aug 13 2015, 02:37 PM
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#41
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Senior Member Group: Members Posts: 3009 Joined: 30-October 04 Member No.: 105 |
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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Aug 13 2015, 03:30 PM
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#42
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Junior Member Group: Members Posts: 82 Joined: 13-July 15 Member No.: 7579 |
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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Aug 13 2015, 04:37 PM
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#43
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Senior Member Group: Members Posts: 1670 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
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. -------------------- Steve [ my home page and planetary maps page ]
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Aug 13 2015, 05:39 PM
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#44
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IMG to PNG GOD Group: Moderator Posts: 2256 Joined: 19-February 04 From: Near fire and ice Member No.: 38 |
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°): 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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Aug 13 2015, 05:47 PM
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#45
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Member Group: Members Posts: 153 Joined: 20-December 14 From: Eastbourne, UK Member No.: 7372 |
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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