Help - Search - Members - Calendar
Full Version: Neptunian System Imaging
Unmanned > Outer Solar System > Uranus and Neptune
Pages: 1, 2
Neptune from Voyager 2. Color is from images with CH4JS, green and orange filter.
Shadows of three moons are visible.
Second image is with possible interpretation.
Yes!!! smile.gif I was hoping you'd focus your imaging magic towards Neptune!
It was only matter of time. smile.gif
Beautiful! I have also worked with these images and interpreted the moon you considered Galatea to be Naiad, but other than that I agree with your interpretation.
Edit: One other question: Which color did you use the CH4JS filter for? It is even redder than the orange filter, but from your listing order it seems like you used it as blue.
CH4JS (with reduced contrast) was used as red color. Another ones: Orange -> green, green -> blue.
So this is false color, but corrected to approximately true color.
That makes good sense. I interpreted too much from the order you listed the filters.
Ian R
Aaaahh... Neptune! I recall taping any mention of the Voyager 2 flyby on TV as a rather eager seven year-old.

Great picture Daniel.
Just so you know Machi, that new image will make its Outreach debut tonight, here in Kendal, in a talk being given to the 10th Kendal Cubs! (all ten of them!) smile.gif
Ian R
Are these the famous shadow-casting cirrus clouds, I wonder?

Click to view attachment
I can't help noticing similarity between clouds on Titan and the ones in that Voyager view of Neptune. In particular the biggest Neptune cloud with its north-south branch does resemble somewhat the big cloud recently seen on Titan. In general, and in both cases, the clouds cover only a small fraction of the globe and are predominantly in the form of long east-west streaks. Of course so much else about the two worlds is so very different. I have no idea whether the morphological similarity signifies anything interesting.

I'm not expert about clouds, so I don't know exactly if it's cirrus, but these are real clouds encircling Neptune's pole.
One of my future image will show this region with higher resolution.
Neptune with cirrus clouds swirling around south pole.
Slightly differences in color are caused by different kinds of filtered images (CH4JS, clear, violet and CH4JS, orange, clear).
Really enjoying this thread Machi.

At the time these images were first released I'd been backpacking through Europe for months and had totally forgotten about the Voyager Neptune encounter. One day on the streets of Paris I saw this incredible blue disk staring back at me from a news stand. I remember just standing there staring at it for ages - I just couldn't believe how compelling and unexpected all that atmospheric structure was!

Now - back to that last image. Can I see a small bright/dark vortex thingy at the pole? Might we be looking at a miniature version of Saturn's 'evil eye'?


"Really enjoying this thread"

I am glad to hear that. tongue.gif

"Can I see a small bright/dark vortex thingy at the pole? Might we be looking at a miniature version of Saturn's 'evil eye'?"

Maybe this little animation (1 frame = 5sec real time) give answer:
Wow, that animation's smooth; had to look hard twice to see that the white clouds were really moving. Nice!!!
Stop that Machi. You're making my eyes hurt blink.gif
Wow! That was neat! It gave the impression of just sitting there watching Neptune silently rotate underneath.
That is so relaxing to watch! Amazing work machi smile.gif
Holy smokes, machi -- that's gorgeous.
That slow motion beauty could make it the opening scene for Stanley Kubrick's grandson's film 2041 A Space Iliad.
Yeah, there's definitely something @ the South Pole...can't tell if it's an innie or an outie, though.

Every planet, especially planets with atmosphere, looks so majestic from close.

"Yeah, there's definitely something @ the South Pole...can't tell if it's an innie or an outie, though."

I see central eye of the south pole "hurricane" and three clouds in him. One cloud is prominent, two clouds are nearly invisible.
I have somewhere article in which authors directly measured wind speed at south pole, perhaps using these clouds.
Partial mosaic of Neptune. Four NAC images over WAC image.
Color from CH4JS, CH4U and violet WAC images.
Another partial mosaic of Neptune. Now at resolution 10.5 km/pix.
Color is added from global images (as uniform color).
Small (10s of km) bright clouds over Neptunian South Pole Region. Narrow angle camera (NAC) image has resolution around 7.4 km/pix.
Details are extremely enhanced (in NAC image), but color (from violet and green wide angle camera images) is very decent.
Subtle shadows under two small clouds are visible.

Not really new, but a nice article about Neptune spin time !

The article uses the puzzling phrase "we thought we knew" to suggest that the radio-based measures of the big planets are somehow invalid, but does not explain why any combination of atmospheric features, observed for any length of time, should give a better estimate of the rotation time of the planetary core. He makes a convincing case that different atmospheric strata, at different latitudes, rotate at different speeds. It is remarkable that he finds as much consistency among multiple features as he does, but why should these supplant the radio-based measures?

Some more informations can be found here:

"So based on those radio signals, we thought we knew the rotation periods of those planets"
But when the Cassini probe arrived at Saturn 15 years later, its sensors detected its radio period had changed by about 1 percent. Karkoschka explained that because of its large mass, it was impossible for Saturn to incur that much change in its rotation over such a short time...

Even more puzzling was Cassini's later discovery that Saturn's northern and southern hemispheres appear to be rotating at different speeds.
"That's when we realized the magnetic field is not like clockwork but slipping," Karkoschka said. "The interior is rotating and drags the magnetic field along, but because of the solar wind or other, unknown influences, the magnetic field cannot keep up with respect to the planet's core and lags behind."
Hey thanks MarcF. That sounds like a clear reason to reject the radio signal-based measure. Earth's field also meanders around and it originates in the liquid regions of the interior IIRC, so no reason to think it works differently on other planets. But I still have to doubt that any number of observations of the visible atmospheric strata are likely to conclusively match Neptune's core rate. Maybe that doesn't matter as long as you have something stable to point to. (At Saturn I suppose it might be harder to find a stable constellation of spots to observe because the seasonal broadening and narrowing of the ring shadows probably influences the rotation rate by thermally by inducing changes in the radius.)
I found even a nicer movie:
Best regards,
New Neptunian moon discovered
I was wondering: being so close to the planet, any chances that it was already present in Voyager imagery?
The article says the discoverer couldn't find it in them.
QUOTE (Explorer1 @ Jul 15 2013, 08:56 PM) *
The article says the discoverer couldn't find it in them.

they seem to have updated it since I posted my comment...
I had the same question and asked Mark. He replied:
I did extrapolate the orbit back to the Voyager era and search the images that were supposed to have captured it. Apparently it is just too small for the Voyager cameras. I seem to recall that their quoted detection limit was comparable to the size of Naiad, the smallest moon that they did find. This object is quite a bit smaller than Naiad.

By the way, the Uranian moon Cupid, discovered in Hubble images in 2003, was also too small for Voyager to detect.
Ian R
Is my memory deceiving me, or has Naiad eluded all attempts at its recovery since the Voyager encounter?
AFAIK, that's correct.
And on that topic, Naiad has now been recovered.
Bjorn Jonsson
A few hours from now, on August 25, 2014 at 03:56 UTC, there are exactly 25 years from Voyager 2's closest approach to Neptune.

I have noticed that mosaics of Neptune are rare, the only mosaics I remember seeing are two global cylindrical maps that first appeared in Science back in 1989 and also the mosaics posted by machi earlier in this thread. So I decided to do some anniversary mosaics. The goal was a global (or near-global) color mosaic and the higher the resolution the better. This resulted in the highest resolution global mosaics of Neptune I have seen (but see the processing description below - maybe it can be argued that these images are in the gray area between mosaics and computer generated images/simulations):

Click to view attachmentClick to view attachment

Click to view attachmentClick to view attachment

There are two versions of each mosaic, an approximately true color/contrast version and a version where contrast has been greatly exaggerated and the effects of global illumintaion removed.

Some notes on the image processing: Voyager 2 usually had to transmit everything to Earth in real time. At the low bit rates possible from Neptune's distance from Earth this meant a long time between successive images. This makes assembling mosaics of Neptune difficult since the images that must be used are obtained over a period of many hours (or even a few tens of hours for big mosaics) and Neptune rotates fast. The best way for assembling big Neptune mosaics is to reproject the images to simple cylindrical projection as I typically do when doing mosaics of Jupiter or Saturn. But in addition I had to remove the effects of global illumination using an inverse photometric function when reprojecting the images, otherwise seams in the map can't be removed with acceptable result. In contrast, this is not the case when dealing with Jupiter or Saturn. I then assembled a mosaic in simple cylindrical projection and then rendered images of Neptune using the appropriate photometric function. This results in some photometric innaccuracies (the photometric function isn't 100% accurate) but despite this the resulting global images are much better than what one gets by using the source images directly since the illumination conditions change fast due to Neptune's fast rotation. All of this was done in grayscale as only green and clear filter images were available. I used mainly green images since they had better contrast than the clear filter images.

In addition to the complications mentioned above, some of Neptune's atmospheric features change very fast (especially the bright clouds) and also the rotation period (or zonal winds) varies a lot with latitude. Major features can drift over 60° in longitude during one rotation of the planet. Because of this the relative longitudinal positions of the cloud features are only approximate in the mosaics above.

The final step was to colorize the grayscale renders. For that I used an earlier global true color image I assembled back in 2009 - it can be seen here.

With all of the caveats above, the result is the highest resolution global mosaics of Neptune that I have seen.

Most of the source images I used were obtained about 2 to 3 days before closest approach when Voyager 2 was 3 to 4 million km from Neptune. I used the calibrated and geometrically rectified images available at the PDS Planetary Rings Node. I used about 20 images.
Ian R
Bjorn, I am in awe of what you've achieved here. Simply magnificent: a real masterclass in working with old yet valuable data. ohmy.gif
Excellent as always Björn!
I think that those images are the best global mosaics of Neptune ever made.
Amazing. Just amazing.
The other day I found an image of Despina's shadow transiting across Neptune in Voyager 2 images taken on August 17. I've seen the wonderful pictures that Ted Stryk and Daniel Macháček have made with moon shadows transiting, but I wasn't sure how much searching they had done for those. So I decided to do a thorough, systematic search through Voyager 2's approach images to see what turned up.

My first step was to download all of the c112xx images taken through Voyager's narrow-angle camera, and search visually through the images for potential moon shadows. Despina's shadows were easy to find, but I also came across some smaller spots that were only about 1 px across, but appeared to be features I could follow from image to image. I kept a spreadsheet of all potential shadows and the images they were found in, then cross-checked them with the PDS Neptune Viewer to see if any of the moons were in positions where they could cast shadows on the planet. Sure enough, a few of those iffy identifications coincided with Naiad and Thalassa approaching the limb of the planet.

Once I had identified a few shadow transits of Despina, Thalassa, and Naiad, I generated a table to predict the times that their shadows might fall on the planet. To do this I simply found an image where the moon's shadow was close to 2nd or 3rd contact, then multiplied by the moon's orbital period. Table in hand, I went through and checked those times against what Voyager was taking pictures of to see if the camera was pointed at the planet during a transit period, and if so, if it got a picture of the moons' shadows tracking across Neptune. I expanded this second pass through the data to include wide-angle camera images starting on the 16th. During this second pass I turned up a few more transits.

Here's a sampling of what I turned up:

Despina's shadow, followed about 10 minutes later by Thalassa's shadow. The gif is enlarged by 2x for better visibility. Here I've applied a 3px unsharp mask to increase contrast and bring out some subtle detail in the clouds:

Click to view attachment

Thalassa and its shadow on the planet at the same time. The inset is 2x the original resolution. I just stretched the histogram here, unsharp masking didn't really bring out any additional detail:

Click to view attachment

Naiad's shadow on August 24 through the wide-angle camera. The inset is also at 2x, and has had a 3px unsharp mask applied to increase contrast between the shadow and the clouds.

Click to view attachment

In addition I was able to identify the spots on Daniel Macháček's photo in the OP as the shadows of Despina and Thalassa, with a guest appearance by Thalassa itself.

My final tally:

18 transits of Despina, with the first observable on August 8. There were 6 more transit events between August 7 and August 24 where Voyager was observing Neptune when Despina's shadow was crossing the disk, but the images were either blurry or the shadow wasn't detectable. I may have seen a shadow in two of these events, but it was only present in a couple of images and may just be noise. The image sequence that Ted Stryk discovered, c1138023-56, appears to be the only set that captured Despina or its shadow through the narrow-angle camera within a day before Voyager 2's closest approach.

9 transits of Thalassa, with the first observable on August 16. There were 4 additional events between August 15 and August 24 where Voyager was looking at the right time, but 3 of these were taken through the wide-field camera on August 22-23 and I wasn't able to see Thalassa's shadow in any of the images taken during this time. No Thalassa transits are visible through the narrow-angle imager within a day before Voyager 2's closest approach, but frustratingly a narrow-angle image, c1136125, would have captured a high resolution image of a Thalassa shadow transit had it been taken about 10 minutes later.

9 transits of Naiad, with the first observable on August 17. There were 4 additional events between August 15 and August 24 with Voyager looking at the right place at the right time. It appears that Naiad's shadow was just below the detection limit in three of these, and the fourth was only visible when Voyager was taking UV images, which have a really low S/N ratio. No Naiad transits are visible through the narrow-angle imager within a day before Voyager 2's closest approach, although it does appear twice in wide-angle images taken on the 24th. The highest resolution views may be the last narrow-angle images to see Naiad's shadow, c1124332-58, back on August 20.

Finally, I was unable to find any shadow transits of Galatea visually, and without that I was unable to generate table where there were windows of opportunity for Voyager to see its shadow. I did search around in Neptune Viewer time periods between August 15 and 18 when Galatea was approaching the limb of the planet and was in position to cast its shadow, but didn't turn up anything. It seems that the shadow either grazed the northern limb of the planet and lasted less time than the gap between images (usually 9 minutes) or missed the planet entirely. No ring shadows were seen, and as Ted Stryk suggested in his conference paper, they are likely well below Voyager's resolution limits.

Not sure where to take this from here. The shadows are much too small and fuzzy to really do much to improve the shape model of these moons, although I suppose they might be usable in refining the moons' orbits if they had some precise astrometry done. Mostly just enjoyed the challenge of finding these things as far back in Voyager's encounter as possible.
Ian R
Fantastic work!
I worked through these images with Mark Showalter after finding the intitial set. The images are certainly interesting, although given the long baseline with Hubble, they unfortunately didn't prove very useful.

Nice work with the images.
It's a shame to hear they're not too useful, but I'm not surprised given the somewhat spotty quality of the images.
this was my attempt 20 years ago to cobble together a complete mosaic of the Neptune ring system. by coincidence, none of the arcs was in view in any of the shots taken during this long sequence. reminds me i should redo this and try to get rid of some of the artifacts . . .
QUOTE (DrShank @ Mar 31 2015, 01:52 PM) *
this was my attempt 20 years ago to cobble together a complete mosaic of the Neptune ring system. by coincidence, none of the arcs was in view in any of the shots taken during this long sequence. reminds me i should redo this and try to get rid of some of the artifacts . . .

Wow ! What a nice image ! Thanks a lot smile.gif
Nice new pictures of Neptune by Hubble, confirming a new Dark Spot with its bright companion in the southern hemisphere !
Reminds me the great time of Voyager 2 flyby. Even if these Hubble images do not have the Voyager 2 resolution, they are quite good and confirm that great science could be made from Earth orbit !
Can't wait the first planetary views from JWST... and from a Neptune-dedicated mission (?)
A few recent Neptune projects:

Here's a narrow angle frame from August 20, I think there's a JPL version floating around. However, it still has the scanline artifacts, and is so deeply saturated that it looks like a monochrome image that's been painted a single tone of blue.

Narrow angle frame of the Great Dark Spot rotating into view on late on August 23. I did some blending of narrow angle clear and green filter images to get more of the limb in view while retaining some of the sharpness of the cirrus clouds. Color is taken from wide-angle images taken simultaneously. Some of the color noise has been suppressed using the Deep Sky Colors HLVG plug-in. Not super happy with the results but I think it's the best I'm going to get considering the available data.

Finally a departing shot of Neptune and Triton on August 31. Dark Spot Jr. is near the cusp on the left, as well as a cluster of cirrus clouds that often popped up over the spot. Dark cloud bands around the south pole are also unusually clear in this image. Not sure why.
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.
Invision Power Board © 2001-2018 Invision Power Services, Inc.