Pluto Atmospheric Observations: NH Post-Encounter Phase, 1 Aug 2015- TBD Options

[scalbers]

A neat paper by Jonathan Fortney shows this ratio to scale (approximately) with sqrt(Rp/H), with Rp being the planet radius and H the scale height. Both indeed decrease this effect for Pluto.

If we assume the scale height of Pluto's atmosphere is 60km and the aerosols have the same height as the gas, then I was able to get a few numbers in the course of comparing various airmass equations. Earth would be about 39 airmasses in the horizontal and Pluto would be 6.4. These numbers would be doubled when looking at grazing incidence from space as in the NH images. I'd still like to come up with a formula for an isothermal atmosphere (exponential density decrease with height) by integrating the thin shell relationship over height and to compare this with the other formulations in Wikipedia. On the other hand, the isothermal case is within just a few percent of the homogeneous (constant density with height) case.

To check the scale height and see why it is much higher than Earth, we might evaluate this expression for Earth and Pluto:

H = kT/mg

H is scale height
T is temperature (a representative value since this varies with height)
k is Boltzmann's constant
m is molecular mass
g is gravitational acceleration

The Wikipedia link above shows this worked example for Earth:

Taking T = 288.15 K, k = 1.3806488x10-13 J/K, m = 28.9644×1.6605×10−27 kg, and g = 9.80665 m/s2 yields H = 8345m

Roughly speaking, if pluto has .07 Earth's gravity and the same T and similar m we'd get about 120km scale height. If the scale height is 60km, then the temperature would still end up being ~140K. So we can check how much the temperature increases with height over the surface value of 44K.

There are other atmosphere posts in the Near Encounter thread as well (e.g. posts #1238 and #1252).

[nprev]

This topic is for discussion of data concerning Pluto's atmosphere (including exospheric phenomena) received after 1 Aug 2015.

[Bill Harris]

As noted earlier:

That has had me doing back-of-envelope scribbling, too. I dunno.

At the Solstices, one pole is 100% in sunlight (with varying sun elevations) for 1/2-year while the other pole is 100% in stygian darkness for 1/2-year. The Equator, OTOH, varies from 1/2-day sunlight _at_ the Equinoxes to 100% sunset (ie, zero Sun elevation, on the horizon) at the Solstices. For arm-waving simplicity, I'm assuming 90 deg polar inclination instead of the 119.xx deg it is. And add to that the variation of solar intensity due to the orbital eccentricity.

The insolation at any point will be the product of the solar intensity (x) a function of the solar elevation (x) a factor of the Sun's time above the horizon (x) whatever I've not thought of. I suspect that we'd need some sort of Calculus to describe that, with sine/cosine wheels to vary things.

Dang. What a can o'worms. Much easier to crank out purty pictures, but less fun.

--Bill

And, as noted:

"Pluto’s insolation history: Latitudinal variations and effects on atmospheric pressure" by Earle and Binzel in April's edition of Icarus is probably the last word on Pluto's insolation history. They've done all the calculus so we don't have to!
For those without access there are various papers on Arxiv which touch on the subject.

The Earle and Binzel article covers a lot, but there has been a wealth of study done on insolation and the atmosphere of Pluto over the past few years. Google "pluto insolation atmosphere" and start digging. The atmosphere of Pluto, which drives the weathering, erosion, transportation, deposition and induration processes of the surface is clearly solar-powered. I've not give much thought to the variations in insolation on a high axial-inclination planetary-body other than imagining that it is out of the ordinary. And the revelations on the structure of the Pluto atmosphere from the post-encounter occultations will drive more research.

--Bill

[lollipop]

I meant to say that Earle and Binzel had sorted out the insolation, in the sense of watts per square metre at various latitudes, and including the orbital eccentricity, polar orientation etc. Of course the in situ measurements of the atmosphere and the images and composition of the surface will tie up theorists for years.
While the insolation is important, any other heat source will have interesting effects on such cold surfaces and such tenuous atmospheres.

[Bill Harris]

Even though the NH encounter increased our knowledge of Pluto and Charon orders of magnitude and many orders of magnitude, respectively, this knowledge is in the form of snapshots of the system. Along with all of the prior data on Pluto the NH data is much like piles of jigsaw puzzle pieces on the table and we'll spend years seeing how the pieces fit together. Three weeks ago we didn't know what the surface of Charon even looked like but now the geomorph people are supposing terrains and processes. Even though Charon is a small airless world, it does have solids that turn to gases and back to solids, seasonally, which is something that the rocky and ice worlds don't have.

Interesting times, these.

--Bill

[Herobrine]

I've previously "unwrapped" the atmosphere/haze from two different sets of LORRI images from SOC.
The second set were nice because they covered the full disk, but this came with substantially lower resolution.
Since the Sun is lighting the haze unevenly around the limb, trying to merge data from around the disk to get a cleaner, higher-resolution profile of scattered light is not a simple task.
Here, I've taken the two LORRI JPEGs and, for each pixel, mapped the value of the sample (0-255) with (the center of) that pixel's distance from my best estimate of the center of the planet. What that gives me is a plot of the combined scattering gradients of all of the different Sun-haze-sensor geometries present in the LORRI frames.

Here are simple plots of that data for both LORRI images.

The vertical axis is sample value (0-255). The horizontal axis is distance (in pixels) from estimated Pluto center. The darkness is an indication of how many pixels are mapped to that spot. Each data point is rendered as a single pixel of black, but with subpixel precision, so the black pixel is distributed across as many as 4 pixels.
Shown in those plots are the mappings of about 32,000 pixels from each image. Specifically, all pixels that have a distance-from-center of between 105 and ~145.65 pixels.

Here is a combination of both images' data, with lor_0299323899's values scaled up slightly to correct for an apparent, small difference in brightness between the two JPEGs.


Pluto center used for lor_0299323899 (pixels): 412.125, 483.75
Pluto center used for lor_0299323929 (pixels): 337.125, 460
^{(center of image's top-left pixel is 0.5, 0.5)}


Edit (2015-08-10): Remade and replaced the "combined" images more carefully, by merging the original data, rather than combining images of both, and using a more precise subpixel render.

I don't have a solid explanation for some of the repeating patterns seen in some parts of the plots. They are not processing artifacts in the sense that they are present in a simple plot without any processing of the data, but given that they have a horizontal spacing of very close to one pixel of distance and occur very close to the mid-point between integer pixels of distance, it seems likely that they are in some way a result of the distribution of pixel distances near certain angles. That isn't to say that they don't represent the actual scattering gradient, but rather probably that near the vertical and horizontal, pixel center distance clusters, horizontally compressing the data in that plot due to a lack of pixels that fall at distances just below and above it near those angles.

[Gennady Ionov]

To be seen the glow of the atmosphere due to Rayleigh scattering need to raise the sensitivity of the image in 8000 times. Then it will look something like this
(old lovely version) (fixed version, really Rayleigh glow is dimmer then Charonshine)
but we does not seen Charonshine on the LORRI frame

Thus the main optical depth falls on the aerosol.
If optical depth of aerosol in 1000 times bigger then for Rayleigh scattering and exponential scale equal to 20 km we obtain a proper image:

[fredk]

Are you saying that, for the geometry of that image, Charonshine on Pluto is very roughly of the same brightness as atmospheric Rayleigh scattering around the limb of Pluto?

What atmospheric parameters did you use for Pluto? And the intensity of Charonshine depends on knowing the absolute albedos of Charon and Pluto - what did you use?

[Gennady Ionov]

Are you saying that, for the geometry of that image, Charonshine on Pluto is very roughly of the same brightness as atmospheric Rayleigh scattering around the limb of Pluto?

What atmospheric parameters did you use for Pluto? And the intensity of Charonshine depends on knowing the absolute albedos of Charon and Pluto - what did you use?

Yes, Charonshine on Pluto is the same brightness as atmospheric Rayleigh scattering.
I used N2 atmosphere with scale 60 km and surface pressure 1.0 Pa.
Albedo of Charon = 0.375, and albedo of Pluto depends from a surface position. Pluto's albedo just is Pluto map.

[fredk]

Sure, Pluto's albedo depends on position, but how did you choose the absolute albedo corresponding to the Pluto map pixel values 1-255? I don't think anyone has made any claim for their map such as that 255 corresponds to albedo = 1 and 128 to 0.5, eg.

Of course, however you chose that shouldn't affect your conclusion that Charonshine is comparable to Rayleigh.

[Gennady Ionov]

Sure, Pluto's albedo depends on position, but how did you choose the absolute albedo corresponding to the Pluto map pixel values 1-255? I don't think anyone has made any claim for their map such as that 255 corresponds to albedo = 1 and 128 to 0.5, eg.

Of course, however you chose that shouldn't affect your conclusion that Charonshine is comparable to Rayleigh.

The resulting LORRI frames in addition to the absolute surface albedo of Pluto is influenced by many factors: the quantum yield of CCD, telescope aperture, mirrors albedo, etc. Consider all this I was not needed, because everything gives approximately linear contribution. Thus, for each of the simulated image, I introduced two parameters - the color of the background and gain. Varying its manually I achieved similarities with LORRI images. By the way, LORRI frames was pretreated and a value of zero and gain different for different images. Therefore, the correlation of the absolute value of the albedo to a pixel value on the map is not required.

By the way, the faint traces of the atmosphere can be seen even daily images of Pluto, if you know what to look for:

Haze brightness in simulated pre-encounter frame is about 2 steps in 256 colours.
On difference (right picture) we can see, that haze glow almost completely compensate glowing on the source frame.

[fredk]

Varying its manually I achieved similarities with LORRI images.

Normalizing to the LORRI sunlit images and taking into account the different exposure times means you can display the Charonshine as it would have appeared in the image (after scaling 8000x, of course). Without knowing the CCD QE etc, you don't know the absolute intensity of Charonshine. But what about the Rayleigh scattering? Is that calculated absolutely given the atmospheric parameters? There are no other images of Rayleigh scattering for reference, unlike the surface of Pluto. How do you decide how bright the scattering will appear on your image? I don't understand how you can compare the intensity of Charonshine and Rayleigh if you calculate the scattering absolutely but not the Charonshine.

By the way, the faint traces of the atmosphere can be seen even daily images of Pluto, if you know what to look for:

That glow around Pluto is probably just scattered light inside the camera. You can see a similar glow in images taken much farther out before closest approach, but the glow's thickness in those images is much thicker relative to the angular (or pixel) size of Pluto. That strongly suggests camera scattered light. The real atmosphere should always appear the same thickness relative to the size of Pluto.

[Gennady Ionov]

But what about the Rayleigh scattering? Is that calculated absolutely given the atmospheric parameters? There are no other images of Rayleigh scattering for reference, unlike the surface of Pluto. How do you decide how bright the scattering will appear on your image? I don't understand how you can compare the intensity of Charonshine and Rayleigh if you calculate the scattering absolutely but not the Charonshine.

I checked my code and found that really I believe that value 255 corresponds to the albedo of 1.0 (in sense all falling light isotropically scatter in half-space). Charonshine light flow is determined relative the Solar light flow from angular size, phase and geometric albedo. Also, the intensity of the Rayleigh emission is determined with respect to the intensity of emission of the white body which isotropically scatter sunlight. Therefore it is possible to compare the Charonshine and Rayleigh glow.

[Bjorn Jonsson]

That glow around Pluto is probably just scattered light inside the camera. You can see a similar glow in images taken much farther out before closest approach, but the glow's thickness in those images is much thicker relative to the angular (or pixel) size of Pluto. That strongly suggests camera scattered light. The real atmosphere should always appear the same thickness relative to the size of Pluto.

There is definitely scattered light around a bright target like Pluto but I wouldn't completely rule out a very faint layer of aerosols/haze in addition to the scattering. Also one problem with the glow around Pluto in the farther-out images days before closest approach is that it may be caused partially by JPG compression artifacts in addition to scattering. Things really do not become completely clear until we see much higher resolution images of Pluto's limb taken before closest approach (i.e. not at high phase angles). Also let's not forget that a haze layer is visible in images of Triton where the phase angle isn't very high.

[Sherbert]

The general conclusion seems to be that Pluto's "sky" would be "space" during the day, but near sunrise and sunset the "haze" of the atmosphere should be discernible. That would be something to see, two "night skies" in one day.

This being the case would "shooting stars" be visible? That is, is the atmosphere "thick" enough to "burn up" incoming debris? Its not very dense, but it is "tall".

Whether visible or not, not all the atmosphere comes from the surface ices. Icy objects entering the atmosphere and "evaporating" could add significantly to Pluto's atmosphere over time. Its not going to replace 500 tonnes per hour thats for sure, but might help maintain the atmosphere's depth and seed ice crystals, via dust and organics, at higher levels of the atmosphere than those materials being transported from the surface reach. Pluto's equivalent of Noctilucent clouds. One might expect atmospheric dynamics would mix the two, but it is very cold and the evidence is that there are distinct layers within the atmosphere.

[fredk]

About the visibility of aerosols/haze in the pre-encounter (low phase angle) images, now that we have observations of that component post-encounter (at high phase angle), could we (Gennady?) do some modelling to estimate their visibility pre-encounter? Of course, we only have observations at high phase angle, and would need to extrapolate to estimate the back-scattered visibility. You'd need to state your assumptions about that, and even better include a range of possibilities as an error estimate.

Even if that turned out to be far too faint to see pre-encouter, you might still find localized bands/clouds of higher density haze.

[Bjorn Jonsson]

I have been attempting to model Pluto's atmosphere to get reasonably good 3D renders at high phase angles. This is a simulation compared to image lor_0299323899_0x630_sci_2.jpg:



The simulated image doesn't have the same orientation as the NH image. I'm using Mie scattering only since Rayleigh scattering is insignificant in Pluto's very thin atmosphere. I suspect that the haze really isn't bluish (my guess is that it's grayish) but MVIC images are needed to know its real color. The corresponding haze brightness in simulated pre-encounter images is ~3 (range 0-255) next to Pluto's limb and this seems plausible but the problem is that I don't know about a possible contrast stretch applied to the JPGs at the NH website. I suspect they are not stretched and one thing implying that they are at least not severely stretched is that there are many intensity levels in the haze in the NH images.

[Herobrine]

This being the case would "shooting stars" be visible? That is, is the atmosphere "thick" enough to "burn up" incoming debris? Its not very dense, but it is "tall".

Not having done any calculations, personally, I'd be surprised if you could ever get a visible "shooting star" at Pluto. I suppose it wouldn't be too terribly difficult to calculate approximations of how hot/bright a large, stony meteor would get, crossing through the densest part of Pluto's atmosphere at 100,000 m/s or something. I just can't imagine it's enough to generate the heat required for it to become visible to the human eye, even as sensitive as that is.
I remember reading about a meteor believed to have been imaged by one of the Mars rovers, but while Mars' atmosphere is something like 1/100th as dense as Earth's, Pluto's is like a thousand times less dense than that.
If someone does the math and it suggests it's possible, I'll believe it, but in my mind, Pluto's atmosphere is so thin, you could scoop it away at 1,000 km/s with a nix-sized scoop without generating enough heat to really glow.
^{I'm frequently wrong, though.}

[ngunn]

The simulated image doesn't have the same orientation as the NH image

Which is which?

[scalbers]

I have been attempting to model Pluto's atmosphere to get reasonably good 3D renders at high phase angles.

Looks pretty interesting. Are you making a certain assumption about things like the phase function, and by extension particle sizes? I agree it wouldn't likely be blue especially with this forward scattering, unless it were just the right size distribution.

This relates to fredk's last post, and to the earlier comment about Triton's haze being visible at various phase angles.

[fredk]

The corresponding haze brightness in simulated pre-encounter images is ~3 (range 0-255) next to Pluto's limb

This is interesting - I wouldn't've guessed it might get that high. (I assume you mean ~3/255, not between 0/255 and 255/255.) But of course this will be strongly dependent on the assumptions - particle size distribution, refractive index, etc.

[Gennady Ionov]

There is definitely scattered light around a bright target like Pluto but I wouldn't completely rule out a very faint layer of aerosols/haze in addition to the scattering.

Haze brightness in simulated pre-encounter frame is about 2 steps in 256 gray steps.
On difference we can see, that haze glow almost completely compensate glowing on the source frame.

[Gennady Ionov]

That glow around Pluto is probably just scattered light inside the camera. You can see a similar glow in images taken much farther out before closest approach, but the glow's thickness in those images is much thicker relative to the angular (or pixel) size of Pluto. That strongly suggests camera scattered light. The real atmosphere should always appear the same thickness relative to the size of Pluto.

I made some modelling to estimate haze visibility in pre-encounter stage and post there blinking pair to compare.

About the visibility of aerosols/haze in the pre-encounter (low phase angle) images, now that we have observations of that component post-encounter (at high phase angle), could we (Gennady?) do some modelling to estimate their visibility pre-encounter? Of course, we only have observations at high phase angle, and would need to extrapolate to estimate the back-scattered visibility. You'd need to state your assumptions about that, and even better include a range of possibilities as an error estimate.

I adjust only optical depth of the haze (its about 0.003 in zenith direction) and used scattering with particle phase function (1 + 5 * mu * mu * mu * mu * mu * mu * mu *(3 + 4 * mu))*(9 / 58.0) which obtain in approximation of the light scattering from Chelyabinsk bolide on winter atmospheric haze. (Rayleigh low is (1 + mu*mu)*(3 / 8.0))
Where mu is cosine of scattering angle. So we have equal scattaring in opposite and forward direction in the case of Rayleigh low and have factor 6 in case aerosol scattering.

[Gennady Ionov]

I suspect that the haze really isn't bluish (my guess is that it's grayish) but MVIC images are needed to know its real color.

Yes, I agree. My scattering simulation in colour (colour does not simulated, just was set manually):

[remcook]

Bjorn, Scalbers: why not blue? It will be blue-ish if the particles are small compared to the wavelength. To have grey scattering, you need fairly large particles, which might be tricky to form at such low pressures. Forward-scattering also tends to strongly increase towards shorter wavelengths. My bet would be blue
To Bjorn, Gennady: what did you assume for the particle phase functions (as a function of wavelength), or refractive indices? They look like really cool simulations.

[Gennady Ionov]

Bjorn, Scalbers: why not blue? It will be blue-ish if the particles are small compared to the wavelength. To have grey scattering, you need fairly large particles, which might be tricky to form at such low pressures. Forward-scattering also tends to strongly increase towards shorter wavelengths. My bet would be blue

I believe that the haze color is grayish for two reasons:
1) Scattering by haze particles are not so much shifted into the blue area as Rayleigh scattering.
2) At least 30% of the scattered light flux is reflected from the reddish surface of Pluto.

To Bjorn, Gennady: what did you assume for the particle phase functions (as a function of wavelength), or refractive indices? They look like really cool simulations.

Colour does not simulated, just was set manually.

[remcook]

Thanks! So, the colour from your colour simulation is basically picked manually. Very interesting about the surface contribution. I guess that will depend a lot on how forward-scattering the particles really are. Looking forward to seeing more data from New Horizons when it will be sent.

[HSchirmer]

... Charonshine on Pluto is very roughly of the same brightness as atmospheric Rayleigh scattering around the limb of Pluto?

...And the intensity of Charonshine depends on knowing the absolute albedos of Charon and Pluto ...

Quick question- just how intense IS Charonshine? Enough to make a 1 or 2 kelvin difference?

Triton's geysers may be powered by as little as 4 kelvins difference in temperature.
The area on Pluto that is illuminated/heated by Charonshine does not have an ice cap.
The area opposite Charon that faces deep space and is not illuminated/heated by Charonshine
has the Tombaugh ice cap.

Is that a coincidence? Or, could the heat of reflected light from tidally locked Charon influence the
location of the equatorial ice cap?

[scalbers]

Good discussion of the additional factors about the haze color. We might further consider what we think the Angstrom Exponent is, a number telling how blue the preference is for scattering that becomes more important if the haze particles are smaller than the wavelength of light. A second factor is that the peak of the phase function can be sharper for bluer light (size parameter varies with wavelength), so would make a bluish cast at the small scattering angles. Perhaps there's some analogy with the particle size distribution from Triton and Titan (or even Mars upper atmosphere) that can help with determining the phase function and how it varies with wavelength.

Here is a paper about Titan's aerosols: http://www.ciclops.org/media/sp/2010/6514_15623_0.pdf

[Gennady Ionov]

Quick question- just how intense IS Charonshine? Enough to make a 1 or 2 kelvin difference?

Charon angular radius is about 600 km / 20000 km = 0.03, its square relative sky hemisphere equal pi*0.03*0.03 / (2*pi)=0.00045, and albedo 0.35, and avarage phase is 0.5.
So Charonshine irradiation only 0.00045*0.35*0.5=8e-5 from Solar irradiation. But Solar irradiation we must divide by 2 due to night time.
In total its make relative temperature difference about 0.00008*2*4=0.00064 (factor 4 from derivative of Stephan-Bolzman low).
In absolute value it is about 0.00064*40K=0.0256 K

[remcook]

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.

[scalbers]

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.

[JRehling]

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.

[fredk]

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".

[nprev]

Copied post from stevesilva over on the 'interesting/boring objects' thread that is relevant here:

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/

[Gennady Ionov]

Thank you, Explorer, Bill!

[Explorer1]

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/

[nprev]

Whups! Sorry. Thanks, Explorer.

[Bill Harris]

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

[Sherbert]

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

[Bill Harris]

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!

[Gennady Ionov]

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.

[scalbers]

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.

[Bjorn Jonsson]

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.

[Sherbert]

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.

[scalbers]

Pretty dramatic flyby from Bjorn 2 posts back. Interesting to see the asymmetry in the atmospheric ring start to increase near the end as the sun pulls away. I was able to turn up my monitor brightness enough to see the Charonshine.

[Gennady Ionov]

Here is an animation I did of the New Horizons flyby that includes atmospheric effects:
https://vimeo.com/136223988
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.

Nice video!
If you make time of Charon pass more slowly, it will look spectacular.
I'm probably wrong somewhere, but I have obtained similar to NH haze images at a scale of less than 30 km...
Yes! My mistake has a copy/paste nature. Haze scale variable does not used at all. Instead Rayleigh scale variable are used.
Its fit value is 48 km:

[Bjorn Jonsson]

I'm probably wrong somewhere, but I have obtained similar to NH haze images at a scale of less than 30 km...

I should mention that my NH image measurements were rather crude and other things in the atmospheric models might be different (and I also cannot completely rule out subtle bugs in my code ). Also the haze/aerosols probably do not decrease uniformly with height, there could be one or more discrete layers of haze and the horizontal distribution of the haze could be non-uniform.

[ZLD]

Bravo Bjorn! The animation is really great and helps put some things in a better perspective, namely the later shots.

[fredk]

Here is an animation I did of the New Horizons flyby that includes atmospheric effects

Beautiful.

You say Charonshine is exaggerated - by what factor? And is the (far) post-encounter Mie scattered light intensity correct relative to the pre-encounter directly sunlit surface of Pluto? Ie, does the simulation use a constant "exposure" for each frame?

I had the impression that the scattered light must be much fainter than the sunlit surface, but now that I look at the LORRI exposures I see that they are comparable, so that means that the scattered light is remarkably bright.

Anyway, this leads me to wonder what the sky would look like from the surface (as others have speculated here already). But what I'm thinking about is the sky near the sun, which would correspond to Mie scattering at large phase angles, where we have a good handle on the phase function from LORRI. We now know that the sky near the sun would be quite bright - in particular, near sunrise/set (optical depth half what LORRI saw) the sky intensity would be comparable to that of the sunlit surface.

Of course our large uncertainty in phase function at smaller phase angles means we wouldn't be very certain how large the glow around the sun would be, and how faint it would get at large angles (eg 90 deg) from the sun. But pick a phase function out of the blue and you could render it...

[Herobrine]

I took the code I wrote to get the value vs radius combined plots of the 2 full-disk backlit LORRI shots and applied it to the 3 partial-disk backlit LORRI shots (lor_029920671, lor_0299206715, lor_0299206716). These are much closer but also much lower quality.
Data from 550,016 pixels across the three images are plotted here. This covers 8.6 times the number of pixels from the other one I posted, and at a much better spatial resolution, so the plot is much richer.

The horizontal axis is the pixel's distance from Pluto's center (left edge is 600 pixels; right edge is 740 pixels).
The vertical axis is the pixel's sample value (bottom edge is 88; top edge is (just below) 256). The sample values of the first two LORRI shots were scaled to match the brightness scaling of lor_0299206716.
All apparent large-scale contours/concentrations apparent here were also apparent in each frame's data individually; they were very consistent.
Artefacts near the bottom are from value-stepping in the original low-quality JPEG data.

Here's the same data plotted the same way, but with each point rendered with a hue based on the pixel's angle from the center of Pluto.

I had to write a different program to make this, and didn't bother with subpixel rendering. Instead, each pixel's data was written into a 560x256 array of lists (2-D binned, in other words) and each list of data was averaged to yield the pixel value. It was then scaled to 280x256 and cropped.

While I was at it, I took some of my new code and rewrote a much better atmosphere unwrapper that's binned and processes each pixel in the images exactly once and so isn't susceptible to a lot of the artefacts that turn up with resampling. I also applied an array column-averaged correction to the sample values of the radius vs angle data before rendering to compensate for the uneven lighting around the disk.

The bottom edge is the surface of the planet; the top edge is 78 pixels above the surface.
The left edge is an angle of 178 degrees; the right edge is an angle of 288 degrees (I might have that backwards...and you might need to subtract them from 360...)
The above version has been contrast-enhanced. The original output is below.

[Bjorn Jonsson]

Beautiful. You say Charonshine is exaggerated - by what factor?

I don't know . I simply added a light source with brightness=0.25 (typically the brightness of light sources is between 0 and 1). If I remember correctly, Gennady worked out the approximate true brightness of Charonshine a few days ago.

And is the (far) post-encounter Mie scattered light intensity correct relative to the pre-encounter directly sunlit surface of Pluto? Ie, does the simulation use a constant "exposure" for each frame?

Yes, I'm using the same set of parameters for almost everything throughout the animation. The only "cheat" is that I altered Pluto's phase function to make it brighter at high phase angles.

I had the impression that the scattered light must be much fainter than the sunlit surface, but now that I look at the LORRI exposures I see that they are comparable, so that means that the scattered light is remarkably bright.

This is true if the JPGs are not contrast stretched (and I don't think they are but I'm not 100% sure). The scattered light is remarkably bright.

Anyway, this leads me to wonder what the sky would look like from the surface (as others have speculated here already).

Here is a quick and dirty test render using the parameters used in the animation. The altitude above Pluto's surface is 200 meters and the field of view is 60 degrees. This should give a very crude idea of what Pluto's sky might look like.

[fredk]

Cool, thanks for that!

About the stretching, you can see clear signs of stretching in some images, eg this Charon image:
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x632_sci_3.jpg
Not only is banding visible by eye and the black regions quite bright, but the histogram shows discrete pixel values, indicating a stretch of about 4:1:

For this post-enc image:
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x632_sci_3.jpg
The histogram also indicates stretching, though not as severe (about 3:1):

But for this post-enc image:
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_2.jpg
There is no sign of stretching:

(Though of course jpegging post-stretch could reduce the signs somewhat.)

[Gennady Ionov]

This is true if the JPGs are not contrast stretched (and I don't think they are but I'm not 100% sure). The scattered light is remarkably bright.

We can preliminary estimate stretching with assessment of the background stars magnitude, if they identify ...
I can evaluate the equatorial grid and put it into the frames...
By the way! We can try to measure the parallax of stars in comparison with images from the Earth. But only for stars closer than 50 pc

[Gennady Ionov]

About the stretching, you can see clear signs of stretching in some images, eg this Charon image:
lor_0299175721_0x632_sci_3
Not only is banding visible by eye and the black regions quite bright, but the histogram shows discrete pixel values, indicating a stretch of about 4:1:
For this post-enc image:
lor_0299206714_0x632_sci_3
The histogram also indicates stretching, though not as severe (about 3:1):
But for this post-enc image:
lor_0299323899_0x630_sci_2
There is no sign of stretching:
(Though of course jpegging post-stretch could reduce the signs somewhat.)

In my simulation I used the next gains table (stretching):
lor_0298996664_0x630_sci_2 = 1.5 ....... lor_0298996694_0x630_sci_2 = 1.5 ....... lor_0298996724_0x630_sci_1 = 1.5
lor_0298996974_0x630_sci_1 = 1.0 ....... lor_0298997004_0x630_sci_1 = 1.0 ....... lor_0299075349_0x632_sci_1 = 1.0
lor_0299123689_0x632_sci_3 = 0.85 ...... lor_0299124574_0x632_sci_1 = 0.95 ...... lor_0299135299_0x632_sci_3 = 1.0
lor_0299135484_0x632_sci_3 = 1.0 ....... lor_0299147641_0x632_sci_3 = 1.0 ....... lor_0299148119_0x632_sci_3 = 0.8
lor_0299148167_0x632_sci_3 = 1.0 ....... lor_0299148215_0x632_sci_3 = 0.75 ...... lor_0299148263_0x632_sci_3 = 0.7
lor_0299165499_0x632_sci_3 = 1.0 ....... lor_0299165548_0x632_sci_3 = 1.0 ....... lor_0299165597_0x632_sci_3 = 1.0
lor_0299165646_0x632_sci_3 = 1.0 ....... lor_0299165695_0x632_sci_3 = 1.0 ....... lor_0299165744_0x632_sci_3 = 1.0
lor_0299174665_0x632_sci_3 = 1.0 ....... lor_0299174713_0x632_sci_5 = 0.8 ....... lor_0299174857_0x632_sci_3 = 0.8
lor_0299174905_0x632_sci_8 = 1.0 ....... lor_0299174953_0x632_sci_3 = 1.7 ....... lor_0299175097_0x632_sci_3 = 1.8
lor_0299175145_0x632_sci_7 = 1.3 ....... lor_0299175604_0x632_sci_3 = 4.0 ....... lor_0299175721_0x632_sci_3 = 4.0
lor_0299175838_0x632_sci_3 = 4.0 ....... lor_0299206714_0x632_sci_3 = 3.0 ....... lor_0299206715_0x632_sci_3 = 3.0
lor_0299206716_0x632_sci_3 = 3.0 ....... lor_0299323619_0x630_sci_2 = 1.0 ....... lor_0299323649_0x630_sci_2 = 1.0
lor_0299323899_0x630_sci_2 = 10 ........ lor_0299323929_0x630_sci_2 = 10 ........ lor_0299324179_0x630_sci_2 = 1.0

In the case of lor_0299323899_0x630_sci_2 stretching may have been produced in 12-bit representation, so no effect on the histogram. (Possible there is stretching in 16 times, so 4 bit were cut)
High background noise and at least 7 visible stars favor this supposition.

[Gennady Ionov]

I calculate the average over the angle values of haze brightness in dependance on the height above the Pluto surface on lit side limb (on the illuminated side the haze glow is practically independent from angle).
Such calculation I made for the original LORRI images and for simulated pictures. Also I estimate PSF of LORRI from far Pluto snapshots (it can be verified from the images of Charon and other satellites).
Now I take PSF as radial function exp(-r*r/1.44)+0.0008*exp(-r*r/100) divaded by norm.

You can get the results in
ftp://gionov:NG@46.45.15.20/_Data/_LORRI/Haze/

For example:



For simulate of haze I used scale 48 km, Rayleigh scale is 60 km.

There is definitely scattered light around a bright target like Pluto but I wouldn't completely rule out a very faint layer of aerosols/haze in addition to the scattering. Also one problem with the glow around Pluto in the farther-out images days before closest approach is that it may be caused partially by JPG compression artifacts in addition to scattering. Things really do not become completely clear until we see much higher resolution images of Pluto's limb taken before closest approach (i.e. not at high phase angles). Also let's not forget that a haze layer is visible in images of Triton where the phase angle isn't very high.

It can be seen that only on the distant image lor_0298996664_0x630_sci_2 haze glowing a little less than light scattering inside the optics.
The picture lor_0299148263_0x632_sci_3_Haze shows appear as the effect of scattering near the limb, and haze glowing far away from the limb.

[fredk]

It's not clear that a psf measured from distant images would capture well the actual scattered light in the optical system in the near shots. Which far shots did you use?

Generally, there's going to be a strong degeneracy between optical system scattered light and atmosphere, so I think it would be very hard to reliably distinguish the atmosphere.

[Gennady Ionov]

It's not clear that a psf measured from distant images would capture well the actual scattered light in the optical system in the near shots. Which far shots did you use?

Mainly I used lor_0298996664_0x630_sci_2 and lor_0299148263_0x632_sci_3, and visual compare a bluring effect with original images.

Generally, there's going to be a strong degeneracy between optical system scattered light and atmosphere, so I think it would be very hard to reliably distinguish the atmosphere.

On *714-716, *899, *929 frames optical system scattered light is negligible, so we can get haze scale and optical depth from this images.
Atmospheric effects on the day lit images remains ambiguous only due to the particle phase function.

[fredk]

Yes, absolutely, I meant it will be hard to distinguish the atmosphere on the pre-encounter images.

[Gennady Ionov]

New simulation shows New Horizons as it went into orbit around Pluto https://youtu.be/zB4Ypa3-T_E
Glowing of the atmosphere too much to make it difficult the observation of the Pluto surface at Charonshine...

[scalbers]

Most remarkable simulations with the atmospheric scattering and all. Is it that the atmosphere is actually "glowing" right at the location of the Charonshine, or simply bright nearby with concerns about scattering in the camera optics?

Is the bright spot on the dark side signifying anything or some type of ghost image effect?

[Gennady Ionov]

Is it that the atmosphere is actually "glowing" right at the location of the Charonshine, or simply bright nearby with concerns about scattering in the camera optics?

I think that here we have not yet seen the Charonshine - it will be seen well on the next turn virtual NH around Pluto (I try increase gain parameter when NH will be opposite to Sun). Scattering by optics plays an important role, but there all the same basically own atmospheric glow.
At the end animation moment about half of the Pluto disc are illuminated by Sun from right side.
Spot on the top is Nix.

Is the bright spot on the dark side signifying anything or some type of ghost image effect?

This is simulation bug at the southern pole point.
I'm fixed it just now!

[scalbers]

Thanks for the update - I now can see the mini-moon at the very end. With the atmospheric glow on the night side, I wonder if/how multiple scattering is being considered, as that would extend the nighttime area of glow.

[Gennady Ionov]

It's the same bug. At one point, I added a small constant 1e-6 to avoid scratch. But she was not so small, and led to diffuse faint glow of the night-side, thickening to the pole.
Multiple scattering does not considired.
New version:
https://youtu.be/8d9hR22SdZo
Version 2: https://youtu.be/Fs9qq3gnAew
Charonshine:


CharonSet:

[Habukaz]

In case anyone missed it, the 29 June stellar occultation by Pluto yielded an atmospheric pressure of 22 microbars; more than 4 times the 5 microbar pressure found by NH.

This suggests that the atmosphere of Pluto was still growing when NH flew past, although, evidently, some model somewhere is wonky.

“I feel pretty secure that Pluto isn’t starting to freeze out,” says Eliot Young, a planetary scientist at the Southwest Research Institute (SwRI) in Boulder, Colorado.

[...]

“How we link the two, we’re still working on,” says Cathy Olkin, a deputy project scientist for New Horizons at SwRI.

Part of the discrepancy between the spacecraft’s observation and past estimates could be due to the indirect way that astronomers derive the value from Earth-based observations. These studies measure pressure some 50–75 kilo­metres above the dwarf planet’s surface, and researchers use assumptions about the atmosphere’s structure to calculate what that number translates to at the ground.

http://www.nature.com/news/pluto-snow-fore...nundrum-1.18274

[fredk]

The press release caption for PIA19880 says we may be seeing crepuscular rays in the terminator region. I've done a very quick and dirty attempt to enhance that detail. Here's the original frame with gamma tweak:

I created a simple circularly symmetric template to subtract from the image, followed by stretching, to bring out the detail in question:

Some of that detail, eg the brightening at the innermost part of the terminator region, is due to processing - a mismatch between the radial profile of the template and the actual image. I'm sure you could do much better with a better template (in particular one that has an elliptical inner boundary).

But the horizontal streaks should be really on the frame. The question is are they on Pluto or not. If you look closely at the lor jpegs, you can see faint striping more or less parallel to these features, apparently due to CCD noise/dark current. This is a stack of those four frames, and shows those CCD streaks running horizontally across the dark disk:

If you compare this image with the enhanced one, you can see that some of the terminator streaks may be due to these CCD streaks - they line up - but not all. So I suspect we really are seeing crepuscular rays. Another bit of evidence is that the streaking is not visible at the outermost radius of the atmosphere.

It's bad luck that the CCD streaks lined up with the solar direction. Perhaps there will be more frames where that's not the case.

[fred_76]

Hello!

Yesterday night I tried to surimpose a view of the "day" side of Pluto with a composite stacking of the 4 images of atmosphere's view taken the 15th july. Here is the result:


This image is "just for fun" indeed...


The correct image is the following one. It is made from the 4 full disk atmo images. The processing is as follows :
- registration on one star
- registration of the whole dwarf planet
- stacking with min/max rejection
- richardson-lucy deconvolution
- log view



The multiple layers structure of the atmosphere is quite intrigating. The dynamic of that structure should be very interesting to understand.

Fred

[scalbers]

That would be interesting to see if a good enough shape model can be developed to simulate these crepuscular rays. It seems that obvious rays would need the mountain height to be somewhat approaching the scale height of the haze, otherwise the contrast would be low.

I have simulated these with my software geared for Earth - I wonder if this could retooled for Pluto...

[Ian R]

My attempt to 'unwrap' the hi-phase angle images, with a hint of color added for artistic purposes:

http://s8.postimg.org/qbg9kqhmb/Pluto_Rays_COLOR.png

[Herobrine]

Looks like ninjas are nearby, but here's an unwrapping of lor_0299236719, lor_0299236749, lor_0299236779, and lor_0299236809. No correction for distortion was performed. A minor level adjustment was performed on some frames to make the brightness curve consistent across all frames. According to the metadata, there was a 0.16% difference in distance-to-target between the first and last frames, amounting to over a pixel of difference in Pluto's diameter, so each image was scaled based on the distance-to-target value in the metadata to correct for this. Alignment was manual, done at 4x scale to allow for some sub-pixel precision. Dimensions scaled-to were 4096, 4098, 4100, and 4103, from nearest to farthest. After alignment, Pluto center was estimated with reasonable confidence that the estimate was within 1 pixel of center at the original scale. The scaled frames were cropped to the region they all shared, yielding a set of 3829x4032 images, which were lightly sharpened with a simple unsharp masking algorithm with radius 6 (1.5 at the original scale) in lieu of deconvolution (because I'm lazy), after which each pixel from each of the four resulting frames (61,754,112 samples in all) was measured for distance from estimated Pluto center and angle from +X relative to Pluto center, and then 2-dimensionally binned in 1 pixel scaled radius x 0.1 degree angle bins (lists of integer sample values, actually, which were later averaged to a floating-point value). The 4000(only 2914 used)x3600 bins were rendered to a 3600x4000 image, which was then cropped to 3600x1748 (to remove incomplete radius space high above the planet), horizontally shifted 25% to place the limb-bound section near the center, gamma-adjusted, and finally scaled to half size (1800x874) to be small enough to upload here.

The horizontal axis spans 360 degrees around the center of the planet, with each horizontal pixel equaling 0.2 degrees. The vertical axis is image-space distance from the center of the planet, with each vertical pixel equaling 0.5 pixels at the scale of lor_0299236719. The bottom of the image is the estimated center of Pluto. Artefacts near the bottom are the result of a shortage of pixels for binning at different angles very near the center. Pluto average radius appears to be about 618 pixels (314 pixels at the scale of lor_0299236719).

Here's a sharpened, level-adjusted, cropped, shifted, and scaled version, including just the limb/terminator and surrounding bright areas.

[HSchirmer]

Quick question- just how intense IS Charonshine? Enough to make a 1 or 2 kelvin difference?

...
In total its make relative temperature difference about 0.00008*2*4=0.00064 ...
In absolute value it is about 0.00064*40K=0.0256 K

Just occurred to me that tiny temperature differences on Pluto that might be enought to drive weather
Those amazing terminator images may have caught "sideways thunderstorms" convecting heat from the days side to the night side.

First bizzare concept - Pluto's N2 ices and N2 atmosphere create a planet-wide equal temperature/pressure bath.
Think of a giant pitcher of ice water, melting or freezing water in a pitcher of ice water does not change the system temperature until all the water is in one phase. N2 ice and N2 atmosphere should be a solid-fluid constant pressure/temperature system.
I've read papers that say Pluto's N2 atmospher and N2 ices should form a contant temperature system, or a constant pressure system , but that idea just sunk in- you literally can not heat up local patches of N2 ice on pluto, it just moves somewhere else, so that all N2 ice on Pluto should be at the same temperature. Instead, you end up heaing up or cooling down ALL surface N2 ice of Pluto. It's sort of a thermodynamic verision of "sea level" on earth.

Second bizzare concept- Tiny variations in heating/sublimation might drive amazing storms in Pluto's atmosphere.
On Earth, a 1% difference in atmospheric pressure creates a high or low pressure system. A 5% difference is a hurricane, a 10% difference is a tornado. Estimates for Pluto are a 1K temp increase doubles the N2 vapor pressure. Wow, a 1K temperature increase creates a 100% pressure difference. So, something as tiny as a .025 K increase in temperature due to relflected light from Charon, might create a 2.5% atmospheric pressure difference- that percentage difference on earth is sufficient to drive a tropical storm.

[alan]

Some topography o the limb visible in these

http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_4.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg

[Gennady Ionov]

Just occurred to me that tiny temperature differences on Pluto that might be enought to drive weather
Those amazing terminator images may have caught "sideways thunderstorms" convecting heat from the days side to the night side.

Second bizzare concept- Tiny variations in heating/sublimation might drive amazing storms in Pluto's atmosphere.
On Earth, a 1% difference in atmospheric pressure creates a high or low pressure system. A 5% difference is a hurricane, a 10% difference is a tornado. Estimates for Pluto are a 1K temp increase doubles the N2 vapor pressure. Wow, a 1K temperature increase creates a 100% pressure difference. So, something as tiny as a .025 K increase in temperature due to relflected light from Charon, might create a 2.5% atmospheric pressure difference- that percentage difference on earth is sufficient to drive a tropical storm.

That was my calculation for the case when there is no atmosphere. Pluto atmosphere is the thermostat and it is necessary find a flow of nitrogen which compensate the additional heat from Charon. The heat flux is 5.67e-8 * 0.0256 * 4 * 40 * 40 * 40 = 0.37 mW / m^2. At nitrogen evaporation heat 200 kJ / kg, this gives 1.9e-9 kg / s / m^2. If the heated area have radius of 300 km we get 530 kg / s. At the same time across the cylindrical surface nitrogen flow was 0.3 g / sec / m. At a pressure of 1 Pa it is about 1.7 kg per square meter of nitrogen accounted, so the speed of the wind caused by light of Charon be only about 0.2 mm / s. It is negligible!

[Herobrine]

The weekly SOC release was about 90 minutes ago. 8 LORRI images were released.
Below is the full list of new images. They are all part of "P_MULTI_DEP_LONG_1_L1" and show a backlit Pluto with atmosphere/haze illuminated.
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_3.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_4.jpg
http://pluto.jhuapl.edu/soc/Pluto-Encounte...0x630_sci_4.jpg

[Nafnlaus]

Tried stacking them to see if I could bring out any detail that wasn't immediately near the limb. No luck.

[alan]

Quote from a recent NASA article

In these unwrapped images, the hazes appear brighter in the evening sky than in the morning sky, possibly suggesting that the hazes and their distribution are controlled by diurnal processes, becoming more concentrated over the course of Pluto’s long day and depleting during Pluto’s long night. Perhaps the haze particles gently rain down onto the surface through the night, staining Pluto with a distinctive reddish cast, or perhaps other atmospheric processes act to move and concentrate the haze.

https://blogs.nasa.gov/pluto/2015/09/25/pluto-at-twilight/

[stevesliva]

Those hazes are *blue*
http://pluto.jhuapl.edu/News-Center/News-A...p?page=20151008

[Nafnlaus]

And how blue they are

Such a simple image - there's not really much to comment about it from a scientific standpoint. But it really packs an emotive punch. Each time I look at that picture it makes me think, "why the heck haven't we visited this world sooner" and "wow, what else is out there in the kuiper belt?"

[ngunn]

And it vindicates the wonderful coloured version of the looking back landscape posted here earlier.

http://www.unmannedspaceflight.com/index.p...st&id=37888
I'm so relieved - I so much wanted to believe that scene was real but couldn't for sure till now.

[Bjorn Jonsson]

The blue color is interesting because it *may* mean that Mie scattering isn't as dominant as would have been case had the atmosphere been grayish (or not blue). Which in turn may mean that the atmosphere might be easier to see in low-phase views of Pluto. If I remember correctly, someone (Gennady maybe) had noticed what could be atmosheric limb hazes in low-phase LORRI images but it could also be due to scattered light - what's really needed are higher resolution low-phase images of Pluto's limb to distinguish possible hazes from scattering in LORRI's optics.

[scalbers]

Those hazes are *blue*
http://pluto.jhuapl.edu/News-Center/News-A...p?page=20151008

Interesting about the blue color. We can consider this in quantitative terms as to what the Angstrom Exponent would be. Typical aerosols on Earth range from 0-2 (gray to light blue). Air molecules are a value of 4 (more blue). What Bjorn is mentioning would be consistent as the smaller aerosols, having the higher Angstrom Exponent, would also have a flatter phase function with less brightness difference between forward and backward scattering. Thus the color can be correlated with both the size and with the phase function.

[remcook]

Though note that that fractal particles, such as found on Titan, can have a pretty high Angstrom coefficient AND are pretty forward-scattering.

[Ian R]

And it vindicates the wonderful coloured version of the looking back landscape posted here earlier.

http://www.unmannedspaceflight.com/index.p...st&id=37888
I'm so relieved - I so much wanted to believe that scene was real but couldn't for sure till now.

If anything, I was *too* conservative with the saturation of the blue hazes!

[scalbers]

Yes perhaps it should be bluer. I suppose we can sample the released RGB image and consider the color ratios, color space, tristimulus functions, gamma correction, and wavelengths of interest and even calculate the Angstrom Exponent.

[Bjorn Jonsson]

In hindsight this test render I posted 2 months ago is interesting:

http://www.unmannedspaceflight.com/index.p...st&p=225265

Not quite saturated enough since judging from the description I've seen of how the MVIC image was processed it should be very close to the true color and contrast of Pluto's atmosphere.

[Gennady Ionov]

Which in turn may mean that the atmosphere might be easier to see in low-phase views of Pluto. If I remember correctly, someone (Gennady maybe) had noticed what could be atmosheric limb hazes in low-phase LORRI images but it could also be due to scattered light - what's really needed are higher resolution low-phase images of Pluto's limb to distinguish possible hazes from scattering in LORRI's optics.

Yes, and I used "flat" phase function with forward/backward ratio equal to 6.
With regard to the published picture, I was confused by the fact that the color of a narrow crescent of reddish surface of Pluto are also blue.
Slightly corrected the color and get this:

[ngunn]

I think you both (Ian and Bjorn) were absolutely spot on with the colour. Colour saturation is a subjective physiological thing. When you look at the NH image the blue atmosphere occupies a very small fraction of your field of view. It looks strikingly blue, but if you actually went there so your whole sky in the direction of the sun was filled with it it would seem less so.

[fredk]

I was confused by the fact that the color of a narrow crescent of reddish surface of Pluto are also blue.

How narrow? Is the sunlit surface actually resolved, or are we just seeing mainly the brightest part of the sky (ie the largest phase angle part)? We may not expect to see any red if the sunlit surface is very narrow. Knowing the time the image was taken, it should be easy to simulate the view from NH and determine how many pixels (or what fraction of a pixel) the sunlit suface is wide.

Also, there will be some atmosphere "on top of" the sunlit surface adding blue light to the surface's reddish light (as much as half the optical depth of the pure-atmosphere lines of sight). Distant mountains on earth tend to look blue for this reason.

[Gennady Ionov]

I can simulate what portion of pixel crescent is sunlight reflected from the surface from the total brightness of the pixel, if it is known shooting time. But using previous experience of modeling LORRI images I can say that it is about 90%.

However, it is possible to analyze other more simple and reliable way without simulation of light tracing.
Unfold the image relative to the horizon

and find the dependence of the maximum brightness for each color channel from the position angle

blue channel overexposed in crescent region, but it does not hurt much to our analysis.
Night side takes an angle of approximately 155 to 335 degrees.
At this angles atmospheric glow reaches its maximum value and almost no change in the crescent. Thus the excess glow is associated with reflection from the surface of Pluto.
On the night side of the weakening of glow due to the fact that we see illuminated the higher layers of haze. Multiply colors on the night side by constant factors, so that at the border with crescent values in channels about the same.

Either the color of haze becomes more blue with height or the image have shifted zero at blue channel.
The color of the reflective surface is obtained as on the left side of picture, in the middle is avarage color of pluto surface:

[Gennady Ionov]

If we multiply the green channel by 0.9, and blue channel by 0.8, we get the color of the surface of Pluto as on the right part of picture:

RGB graph:

And corrected image in comparing to original:

[scalbers]

I thought it would be interesting to compare simulated blue skies on Earth using my ray tracing software to what we see on Pluto. In a rather clean atmosphere case, I show Earth skies to have a G/B ratio of about .71. This is after converting the radiances to an RGB image for display. Meanwhile the released image has a somewhat variable G/B ratio from roughly 0.68 to 0.81. I wonder why this ratio should vary with the intensity if all of the color balancing is done correctly? Nonetheless if we take a "typical" value in the released image of .76 this would work out to an Angstrom Exponent of about 3.3. This is on a par with the bluest of hazes we see on Earth though not quite a pure Rayleigh scattering value of 4.

If the vertical color gradient in the released image is real, then we might surmise the Angstrom Exponent increases with altitude and the aerosol particle size also decreases with altitude.

[fredk]

At this angles atmospheric glow reaches its maximum value and almost no change in the crescent. Thus the excess glow is associated with reflection from the surface of Pluto.

It's completely unclear what you're saying here. On the night side, as I think you say, we're seeing pure atmosphere and no sunlit crescent. On the day side we're seeing atmosphere plus thin sunlit crescent.

But, as I think you also say, the atmosphere we see on the night side is typically higher than the atmosphere we see on the day side. The low-elevation atmosphere is in the shadow of Pluto on the night side. But on the day side we can see the atmosphere right down to the surface of Pluto. This means that, even if the suface of Pluto was perfectly black, we'd expect the day side atmospheric glow to appear brighter than the night side glow!

Of course Pluto is not black and there will also be a contribution to the day side from the thin sunlit crescent. But here's the key point: in the absence of modeling, we don't know how much of the excess brightness between night and day is due to the fact that we see lower atmosphere on the dayside, and how much is due to the fact that we also see sunlit crescent on the dayside! In other words, we don't know how much the sunlit surface contributes to the day side brightness, so we can't set colours according to the average surface colour!

In addition, as scalbers pointed out, the day-night colour differences you're seeing may simply be due to the atmosphere being bluer higher up, which is consistent with small particles clumping into larger particles as they fall, as we'd expect. Or they may be due to nonlinearity of the RGB levels, due maybe to gamma adjustment.

To sum up, we have no reason to mistrust the image we've been given and nothing upon which to base a quantitative adjustment of it.

[scalbers]

That's largely true though I'd be interested to refine the assessment of the maximum blueness in the upper atmosphere. The image drops to a G/B ratio of around 0.6 in the top and faint part. In theory it should stay above about 0.70 at least from my various assumptions.

[Gennady Ionov]

It's completely unclear what you're saying here. On the night side, as I think you say, we're seeing pure atmosphere and no sunlit crescent. On the day side we're seeing atmosphere plus thin sunlit crescent.

But, as I think you also say, the atmosphere we see on the night side is typically higher than the atmosphere we see on the day side. The low-elevation atmosphere is in the shadow of Pluto on the night side. But on the day side we can see the atmosphere right down to the surface of Pluto. This means that, even if the suface of Pluto was perfectly black, we'd expect the day side atmospheric glow to appear brighter than the night side glow!

Yes, it is obvious that the night side is darker than day side. I tryed to say that in the case of the black surface of Pluto on the day side will be almost constant brightness. And the deviation from a constant glow is caused by the surface, which is due to the optical blur mixed to atmospheric glow. So it can be used of caliberate of color chanels.

[Gennady Ionov]

That's largely true though I'd be interested to refine the assessment of the maximum blueness in the upper atmosphere. The image drops to a G/B ratio of around 0.6 in the top and faint part. In theory it should stay above about 0.70 at least from my various assumptions.

Yes, if we multiply blue channel by 0.8 than the result will be more consistent with the theory.

[fredk]

I tryed to say that in the case of the black surface of Pluto on the day side will be almost constant brightness.

Do you mean constant brightness as a function of position angle around the disk, on the day side? I don't see why that should be constant. The phase function should peak at the largest phase angles, so the atmosphere should be fainter towards the ends of the day side. (Of course the important question is how fast the phase function drops, which is model-dependent.)

This could be easily checked by rendering the atmosphere with a black surface, keeping in mind that we don't know the phase function so a range of possibilities should be considered.

[Gennady Ionov]

Do you mean constant brightness as a function of position angle around the disk, on the day side?

Yes! Exactly!

I don't see why that should be constant. The phase function should peak at the largest phase angles, so the atmosphere should be fainter towards the ends of the day side. (Of course the important question is how fast the phase function drops, which is model-dependent.)

If distance at the shooting time was about 50,000 km, the change in the scattering angle was about 1 degrees with an angle value about 15 degrees. The reason I say that is ALMOST constant.

This could be easily checked by rendering the atmosphere with a black surface, keeping in mind that we don't know the phase function so a range of possibilities should be considered.

I try to do it for MVIC:

Distance to Pluto is 175000 km. Take image time is 15:21:30 UTC July 14 if original image does not scaled.

If we turn on surface with map http://laps.noaa.gov/albers/sos/pluto/pluto_rgb_cyl_16k.png
we obtain

To comparing original MVIC image and with multiplied blue by 0.8 and green by 0.9:

[remcook]

A tweet from the Pluto session at the DPS meeting: Hayley Williamson ‏@hayleynw92 :

"Pluto haze is probably aggregate particles to allow for blue color (small particles) and forward scattering (large particles). #DPS15"
Basically follows the discussion here.

[alan]

Other results from the conference showed that Pluto’s tenuous atmosphere — its surface pressure is only ten millionths that of the Earth’s atmosphere — is colder and more compact than initially expected. That suggests that far less of the atmosphere is escaping to space than expected.

“This changes our thinking of the long-term evolution of Pluto and its atmosphere,” said Leslie Young of the Southwest Research Institute. That includes losing far less of the ice on Pluto’s surface than originally thought. “The atmosphere has some huge implications for the history of the geology of Pluto.”

http://spacenews.com/new-horizons-reveals-...es-about-pluto/

[scalbers]

On an AGU poster I recall something like a .0045 optical thickness (tau) for the haze with a scale height of ~50km. It's interesting to note this tau is similar to what we see on Earth for stratospheric aerosols when they are enhanced somewhat due to volcanic emissions (such as presently). This relates to the brightness of twilight on Earth about 25-30 minutes after sunset.

When we're talking about "strong" forward scattering, I wonder what the peak of the phase function is for a scattering angle of zero degrees (180 phase angle)? The phase function is a quantity that integrates to 1 over the sphere. For the analogous atmosphere of Titan, this function is shown in figures 12.20 and 12.21 here: http://www.ciclops.org/media/sp/2010/6514_15623_0.pdf. Scaling factors are used in the figures to help separate the individual plots. The peak is thus nearly 1000. This indeed is what we'd see on Earth for pretty large particles in the haze, as would happen in a dusty day with a condensed bright aureole around the sun with around half of the scattered light contained in just a few degrees of radius.