New Horizons: Near Encounter Phase |
New Horizons: Near Encounter Phase |
Jul 28 2015, 12:06 AM
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#1246
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SewingMachine Group: Members Posts: 316 Joined: 27-September 05 From: Seattle Member No.: 510 |
This is an improved version of a CGI rendering I posted in another thread utilizing the new map and Bjorn's map of Charon with the high resolution frames added. Colorization is false, bump mapping cloned, and global orientations altered to make a prettier picture, but it does give an idea of what's going to be possible as the extant imagery continues to expand and improve.
Pluto and Charon by Orion Moon, on Flickr Also, a perspective view of the high-resolution images. Pluto Perspective Rendering by Orion Moon, on Flickr -------------------- ...if you don't like my melody, i'll sing it in a major key, i'll sing it very happily. heavens! everybody's all aboard? let's take it back to that minor chord...
Exploitcorporations on Flickr (in progress) : https://www.flickr.com/photos/135024395@N07/ |
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Jul 28 2015, 02:44 AM
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#1247
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Member Group: Members Posts: 244 Joined: 2-March 15 Member No.: 7408 |
That's beautiful, Exploit!
So, I took a first stab at writing a program to unwrap the atmosphere from Pluto, from the 3 LORRI images, and here's the first thing it spit out. That's the atmosphere/haze unwrapped radially from due left to due down (90-degree arc) in the LORRI images. The bottom pixel row is the surface of Pluto, as defined in my post a few posts back. The top row is 127 pixels out from the surface, or about 227 kilometers. It dawned on me, after generating this, that this must be essentially the same thing that haze graphic was showing at the last press conference. In fact, looking at the two, I see all of the same shapes; mine just goes about twice as high. If I knew how to apply a LUT in GIMP, I'd color it the same and compare them. I guess I could write a LUT into my program, but that sounds suspiciously similar to work. I'll probably play with the code for a while and edit this post to update it if I come up with anything new or interesting. Edit: Here's a wider range of angles (100 degrees instead of 90) and half the height (about 114 km or 71 miles) done at a higher sampling for better results. And finally, I got around to applying a LUT of some sort, though I don't have the same kind used in that graphic. That's a blink between the graphic used in the press conference and my own, made from the LORRI images with the little program I wrote. Mine covers more to the right and less to the left, compared to the presentation graphic, so it's offset. Note: I just roughly eyeballed the vertical scaling and alignment of the two for that GIF. |
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Jul 28 2015, 04:04 AM
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#1248
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Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
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Jul 28 2015, 11:03 AM
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#1249
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Member Group: Members Posts: 423 Joined: 13-November 14 From: Norway Member No.: 7310 |
Part of the northmost higher-resolution limb really looks like Venus' surface close up.
The surface there looks relatively young, with few well-preserved craters, but then again, it's also not far from the supposed polar cap. Here's the Venus-looking bit: Really strange-looking terrain. I was wondering why they did not download thumbnails of their observations; maybe they did download some. Heavily eroded crater? I'd also like to know where the full-disk "farewell" image comes from; there are three similar images in SOC that only cover a little more than 1/4 of the disk but nothing in there for the rest of the disk. Also, Nix. The full-ring images are opnavs, taken much later. http://www.planetary.org/blogs/emily-lakda...k-at-pluto.html This post has been edited by Habukaz: Jul 28 2015, 11:36 AM -------------------- |
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Jul 28 2015, 11:08 AM
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#1250
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Senior Member Group: Members Posts: 2997 Joined: 30-October 04 Member No.: 105 |
QUOTE The atmosphere one or two scale heights up would be in "permanent" sunlight And, IIRC, the scale height of the atmosphere is/was given as ~60km, pre-NH. I've not seen the current buzz on that value. One interesting paper I came across the other day: Thermal tides on Pluto - LESIA - Observatoire de Paris in PDF format: http://www.lesia.obspm.fr/perso/bruno-sica..._waves_Ic10.pdf Although Pluto has a thin and cold atmosphere, it is proving to be hardly boring. --Bill -------------------- |
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Jul 28 2015, 11:09 AM
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#1251
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Junior Member Group: Validating Posts: 83 Joined: 14-October 14 Member No.: 7282 |
Here are Pluto images of 7-12 of July, reprocessed to increase resolution. Hope they can be useful for creating a detailed global map.
http://s1.sendimage.me/7SoVqwBD.png http://s1.sendimage.me/K6OfQwBE.png http://s1.sendimage.me/xlkRjwBF.png http://s1.sendimage.me/i40SkwBG.png http://s1.sendimage.me/prGX1wBH.png http://s1.sendimage.me/5dGqawBI.png |
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Jul 28 2015, 02:55 PM
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#1252
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Rover Driver Group: Members Posts: 1015 Joined: 4-March 04 Member No.: 47 |
I wonder if the gaseous component would have been visible to the camera if haze wasn't present. Rayleigh scattering at microbar levels is very small. Also, the fact that Rayleigh scattering is pretty uniform (light is scattered to all directions equally), making that in the direction of the Sun, it will block most of the sunlight, instead of enhancing it (why the sun becomes redder, not bluer during sunset). Methane gas will make it worse, since it absorbs at red wavelengths. I think we might be helped here by enhanced scattering in the forward direction, as is seen in Titan haze. I once did the calculation of how much more air an observer standing on Earth looks through when looking at the Sun at sunrise/sunset versus looking at the zenith, and the answer was about 16x. Therefore, someone in space looking at the sunset would be looking through 32x as much air as the ground-bound observer looking up at the zenith. For Pluto, however, this ratio will be lower because the scale height is much higher – about 60 km for Pluto versus 8 km for Earth. All of that said, the question is what is visible in the first place – 32 times zero is still zero. It seems to me that Pluto's atmosphere when backlit would not be visible to an observer because it is so much thinner than Earth's. But this gets into issues of camera (or eye) sensitivity. 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. Indeed most of the light we are seeing is aerosols as the team stated. I'm simply wondering what the gas alone (and combined with the aerosols) would have looked like, both to the camera and to a human observer at various times of day and vantage points. The solar declination is now at about 51.5 degrees, so anywhere north of 38.5N has a midnight sun. I think you wouldn't really see anything of the atmosphere in the gas-only case in either case. If Titan-like, you might see a red glow (it is a bit more absorbing at blue wavelengths). |
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Jul 28 2015, 04:32 PM
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#1253
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Senior Member Group: Members Posts: 1620 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
Rayleigh scattering is indeed pretty uniform (within a factor of 2 at different angles), though there isn't enough atmosphere present to noticeably block the sunlight. While we've heard about the pressure in microbars it might be interesting to characterize what the optical depth is with the density and scale height factored in.
Based on my back of my envelope so far I agree you wouldn't see the gas only atmosphere on Pluto. However if the Sun had Earth's intensity I think it would probably be faintly visible. With the aerosols, it would be interesting to quantify how bright the halo is the LORRI images. If future images are available at various phase angles it would tell a lot more about these aerosols. Thanks for mentioning the sqrt(Rp/H) relationship. It is consistent with a related formula I've seen for a optical thickness of a thin layer above an observer. -------------------- Steve [ my home page and planetary maps page ]
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Jul 28 2015, 05:07 PM
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#1254
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Director of Galilean Photography Group: Members Posts: 896 Joined: 15-July 04 From: Austin, TX Member No.: 93 |
I dunno. The human eye is actually a pretty decent optical system. Fully night-adapted, it can detect sources with as little as 30 photons per second. (taken from http://www.astr.ua.edu/keel/techniques/eye.html) I would bet that if a human astronaut was orbiting Pluto and fully dark adapted, she would be able to see the diamond ring around the planet - or at least a slight brightening around the no-stars circle. With all our constant light pollution here on Earth, and our tendency to go directly from brightly lit spaces to dark areas, we don't really appreciate how capable our eyes are. The LORRI image is 1/7s, so a rough comparison would be to take a digital camera and set the F stop to 12.5 (LORRI's f-stop, human eye is about f/3.2 fully dark adapted, taken from http://www.boulder.swri.edu/pkb/ssr/ssr-lorri.pdf), and take an 1/8 of a second shot. The LORRI shot shows ~102 in the "dark" areas, and about 200 in the "light" areas, so take a shot of a dark sky with part of it covered up so that it is "black", and compare the average noise on the black half to the signal on the uncovered half. If you can find a feature (such as milky way clouds or more likely, light pollution) about 2x the noise floor, see if you can detect that feature visually after full dark adaption (45 minutes). Make sure your camera is set to RAW mode, and no white balance or other shenanigans. LORRI does get a better noise floor due to being in the cold of deep space.
Looking at it another way, the eye at night integrates at about 1/30th of a second vs LORRI's 1/8, but if I understand the difference between the eye f-ratio and LORRI's f-ratio I think the eye gets an advantage there. However, LORRI's QE peaks at about 45%@700nm (http://www.npk-photonica.ru/images/ccd47-20fi_aimo.pdf), while the human eye's night vision peaks at 507nm (http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html), so it is possible the haze is outside our eye's spectral window. I couldn't find any articles on the visible spectrum of Titan's high altitude haze layer for comparison, but I did see a couple of estimates of 1,000nm particle sizes. Maybe Pluto's lower pressure and less UV counteracts the lower gravity, allowing larger particles to fall out leaving the smaller ones. If we get Ralph spectral data we should know better the color of the haze (and by Mie scattering the particle sizes). If my math is right, the sun is just below 1 LORRI pixel wide from Pluto. With accurate SPICE kernels it should be possible to place that pixel on the images. I'm at work right now and can't check against Eyes on the Solar System. And now the back of my envelope is well and truly full. -------------------- Space Enthusiast Richard Hendricks
-- "The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke Mother Nature is the final inspector of all quality. |
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Jul 28 2015, 06:27 PM
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#1255
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Rover Driver Group: Members Posts: 1015 Joined: 4-March 04 Member No.: 47 |
Some quick calculation with spherical shells with hydrostatic equilibrium, R=1185km, N2 atmosphere, uniform 44K temperature, surface gravity of 0.6 m/s2, but with Rayleigh scattering parameters for a H2 atmosphere (won't make a big difference), I get about 2e-9 slant optical thickness at a microbar level at visible wavelengths.
So, indeed very little. With blocking the sun I meant all the light that is scattered (which is very little), extrapolating the case that it IS caused by Rayliegh scattering, and then arguing against it " If future images are available at various phase angles it would tell a lot more about these aerosols." There is even solar occultation data, which should get you the spectral slope, giving an indication of particle size. |
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Jul 28 2015, 06:48 PM
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#1256
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Senior Member Group: Members Posts: 1620 Joined: 5-March 05 From: Boulder, CO Member No.: 184 |
Good envelope thoughts to ponder there. I agree with the aerosols one could probably see the glow as long as the sun is blocked behind something and you're looking right next to the sun (as in the LORRI images or from the surface). If you're standing on the surface it might be best to be with the sun right below the horizon, so sunlit terrain wouldn't interfere with your dark adaptation.
Note the phase function of aerosols can change quite a bit depending on size distribution. Typically the brightness right next to the sun would be around a couple orders of magnitude more than in other parts of the sky for an observer on the surface. Perhaps the Charonshine images will give another reference on how LORRI responds to faint extended objects. We'll need another envelope perhaps for that Incidentally noctilucent clouds on Earth might be another case to consider, occurring at roughly similar pressures, except here we have condensation of water vapor. -------------------- Steve [ my home page and planetary maps page ]
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Jul 28 2015, 07:59 PM
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#1257
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Junior Member Group: Members Posts: 31 Joined: 8-October 12 Member No.: 6692 |
Does anyone know how often there is a Charon-eclipse by Pluto, if there are any ?
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Jul 28 2015, 08:02 PM
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#1258
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Senior Member Group: Members Posts: 1729 Joined: 3-August 06 From: 43° 35' 53" N 1° 26' 35" E Member No.: 1004 |
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Jul 28 2015, 08:47 PM
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#1259
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Member Group: Members Posts: 807 Joined: 3-June 04 From: Brittany, France Member No.: 79 |
Here is my take on the LORRI mosaic, rotated and very slightly sharpened. I colorized it with the 2x2 color picture of Pluto. Since this color low resolution picture and the B&W LORRI mosaic didn't overlap correctly with simple rotation, translation or shearing, I cut the color picture into 50 segments. Then I warped each segment to match the LORRI mosaic. It took me hours of work on Gimp but the result is worth it
Edit: Herobrine pointed out that a small band of terrain was missing in my mosaic. I improved the stitching to correct it and updated the mosaics. -------------------- |
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Jul 28 2015, 09:59 PM
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#1260
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Member Group: Members Posts: 223 Joined: 13-October 09 From: Olympus Mons Member No.: 4972 |
Thanks Antdoghalo. Incidentally I'm still getting better displays of the 16K version (thanks Herobrine for posting your included mosaic) using Firefox compared with another browser. Good idea with the FOC map. I've seen another effort to do this type of combination, and I can try using the FOC map as a background instead of the July 7 NH map. With Science On A Sphere we're also working on an animation that shows the history of the maps over the decades. Unfortunately I am unable to view images as large as 16K. Are you working on a map of Charon too? The animation sounds like it will be awesome to see when it's done. -------------------- "Thats no moon... IT'S A TRAP!"
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