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Björn Jónsson • Sep 14, 2016

A deep dive into the highest-resolution Voyager Jupiter data

A few weeks before the first Juno high-resolution imaging, I decided to take a look at Voyager color images at various resolutions, with particular attention to high-resolution mosaics. The idea was to get at least some idea of what might be expected from Juno. This resulted in several mosaics, which I will show in order of their resolution, starting with the lowest resolution mosaic.

With the exception of one mosaic (the white oval mosaic), the source images are in all cases green- and violet-filtered images. Most of the hi-res Voyager color observations were performed using this filter combination. This is not optimal for constructing true-color images, but I think I managed to get reasonably realistic color. Here is a quick and dirty global image I used as a test -- the two source images are orange and violet filtered.

Voyager 1 global mosaic of Jupiter
Voyager 1 global mosaic of Jupiter This approximately true color view of Jupiter was created using orange and violet filter images as Voyager 1 flew by in March of 1979.Image: NASA / JPL-Caltech / Björn Jónsson

Not bad, but I suspect the color could be improved a bit. The color processing I used for the hi-res mosaics is comparable to what I did in this global view. The features shown in the mosaics are semi-randomly selected -- I simply selected images where mosaics could be constructed, color was available and the images looked interesting in some way.

I processed the color of each mosaic in two ways, making one version with approximately true color/contrast version and another where the color and contrast has been exaggerated and the image sharpened to better show various details. Some of the images below are shown in both versions; for both versions of all images, visit this forum thread. The contrast stretch varies for the different mosaics and depends on things like scene brightness and contrast. North is up in all cases. The mosaics are 10-15% bigger than the original data, i.e. they are slightly oversampled to avoid losing details. In all cases the indicated resolution applies to the original data. As usual I reprojected the images to simple cylindrical projection, did all of the mosaicking and color processing there and then rendered an image using the viewing geometry close to the mid-time of the mosaic's imaging sequence.

Jupiter's North Equatorial Belt and North Tropical Zone
Jupiter's North Equatorial Belt and North Tropical Zone This is a nine frame Voyager 1 mosaic focusing primarily on Jupiter's North Equatorial Belt (NEB), the North Tropical Zone (NTrZ) and their turbulent boundary. A jet stream is visible in central NTrZ, and examples of the NEB plumes are also visible. Gravity waves can be seen below and to the right of center. The images in this mosaic were acquired from a range of ~2.4 million kilometers from Jupiter's center at a resolution of ~24 km/pixel. Color, contrast, and sharpness have been enhanced to better show various details.Image: NASA / JPL-Caltech / Björn Jónsson
Jupiter's North Tropical Zone
Jupiter's North Tropical Zone This Voyager 1 mosaic shows the southern edge of the North Tropical Zone near the top of the image, and the NTrZ/NEB boundary in the lower portion. The images comprising this mosaic were acquired at a distance of ~1.4 million kilometers from Jupiter's center at a resolution of ~14 km/pixel.Image: NASA / JPL-Caltech / Björn Jónsson
Wide angle context view
Wide angle context view The white boxes denote the location of the mosaic above.Image: NASA / JPL-Caltech / Björn Jónsson
Barge on Jupiter
Barge on Jupiter This high resolution Voyager 2 mosaic shows the area near a brown barge in Jupiter's northern hemisphere. The barge is partially visible at upper right. These barges usually appear at the northern edge of the North Equatorial Belt (or sometimes within the North Equatorial Belt) near 16°N. The images in this mosaic were acquired from a distance of ~1.3 million kilometers from Jupiter's center at a resolution of ~13 km/pixel. Color, contrast, and sharpness have been enhanced to better show various details.Image: NASA / JPL-Caltech / Björn Jónsson
’Cross sequence’ of the Great Red Spot (exaggerated color)
’Cross sequence’ of the Great Red Spot (exaggerated color) About 20 hours before closest approach, Voyager 1 took a 'cross sequence' of images across Jupiter's Great Red Spot (GRS). This was for—among other things—supporting an observation for the IRIS instrument, which was observing the GRS at the same time. The images in this mosaic were acquired from a distance of ~1.25 million kilometers from the center of Jupiter at a resolution of ~12.5 km/pixel. Color, contrast, and sharpness have been enhanced to better show various details.Image: NASA / JPL-Caltech / Björn Jónsson
Global context map for GRS cross sequence mosaic
Global context map for GRS cross sequence mosaic Image: NASA / JPL-Caltech / Björn Jónsson
Southern oval on Jupiter
Southern oval on Jupiter Voyager 1 obtained this mosaic of a southern oval about 12 hours before closest approach. In addition, two color frames obtained almost one hour earlier were used for the rightmost part of the image to get complete coverage of the easternmost part of the reddish oval that is conspicuous in this mosaic. The oval is located near latitude 60°S and is about 5000 km across. Like the Great Red Spot. it is anticyclonic.

Farther south, the south polar hood/haze is obvious. Its northern edge is usually near 66°S. It is bluish in the enhanced image here, both due to the stronger blue color (relative to red/green) in the polar hood and also because of Rayleigh scattering near the limb. Observations have shown that the top of the main cloud layer is lower in the polar regions than elsewhere.

When Voyager 1 obtained these images it was less than 1 degree south of Jupiter's equatorial plane, while the oval is located near latitude 60°S. This makes the oval highly foreshortened; in reality it is much closer to a circular shape than the images above suggest. These images were acquired at a distance of ~930,000 kilometers from Jupiter's center at a resolution of ~9 km/pixel. Color, contrast, and sharpness have been enhanced to better show various details.Image: NASA / JPL-Caltech / Björn Jónsson
Southern oval on Jupiter (viewed from directly above)
Southern oval on Jupiter (viewed from directly above) Image: NASA / JPL-Caltech / Björn Jónsson
White Oval DE, Jupiter
White Oval DE, Jupiter About 10 hours before closest approach to Jupiter, Voyager 1 acquired three 1x3 narrow angle green filtered mosaics of one of the three big, white ovals that were present in the South Temperate Zone at latitude 33°S during the Voyager flybys. These ovals formed in 1939–1941 and had been shrinking since then. They were named oval BC, oval DE and oval FA. In 1998, ovals DE and BC merged into a single oval that was named oval BE. In 2000, oval BE absorbed oval FA to form what was named oval BA. In 2006, the color of oval BA changed from white to red, similar to the Great Red Spot. It still has a strong, orange color. This mosaic shows white oval DE. This oval is visible at lower right in this global mosaic of Jupiter. The images in this mosaic were acquired at a distance of ~800,000 km from Jupiter's center at a resolution of ~8 km/pixel. Color, contrast, and sharpness have been enhanced to better show various details.Image: NASA / JPL-Caltech / Björn Jónsson
Wide angle context view (approximately true color/contrast)
Wide angle context view (approximately true color/contrast) Image: NASA / JPL-Caltech / Björn Jónsson
Southern boundary of White Oval DE
Southern boundary of White Oval DE Image: NASA / JPL-Caltech / Björn Jónsson
Limb of Jupiter from Voyager 2 (approximate true color version)
Limb of Jupiter from Voyager 2 (approximate true color version) Note how hints of Jupiter's blue sky are visible above Jupiter's limb.Image: NASA / JPL-Caltech / Björn Jónsson
Limb of Jupiter from Voyager 2
Limb of Jupiter from Voyager 2 This Voyager 2 mosaic shows Jupiter's limb. The images comprising the mosaic were acquired at a distance of ~745,000 km from Jupiter's center at a resolution of ~7 km/pixel. Color, contrast, and sharpness have been enhanced to better show various details.Image: NASA / JPL-Caltech / Björn Jónsson
Highest resolution Voyager 1 color view of the Great Red Spot
Highest resolution Voyager 1 color view of the Great Red Spot Less than 8 hours before closest approach, Voyager 1 obtained a green and violet filter mosaic with its narrow angle camera (NAC) covering most of the Great Red Spot (GRS)—a total of 28 images. Here the effects of the varying illumination across the mosaic have been removed. At ~6 km/pixel, this is the highest resolution pre-Juno color data for Jupiter (all of the higher resolution Voyager images are clear filter images). Lower resolution orange, green and violet images from Voyager 1's wide angle camera (WAC) are also used to show the GRS periphery and surrounding areas. Color, contrast, and sharpness have been enhanced to better show various details.Image: NASA / JPL-Caltech / Björn Jónsson

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