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Voyager and Galileo Images of Ganymede, The Ganymede images and mosaics thread
Bjorn Jonsson
post May 18 2007, 09:43 PM
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I've been processing some of the high resolution Galileo Ganymede images recently. As far as I know the two mosaics below have not appeared at the official websites (at least not in this form) so in a sense they are 'new'.

The first one was obtained during the G1 flyby in 1996. It covers a part of Memphis Facula which is centered at roughly 15N, 132W. The images were obtained at a distance of approximately 5000 km from Ganymede's center.
Attached Image


The second one was obtained during the G28 flyby in May 2000. It is centered near 14.5S, 319.7W. The images making up the mosaic were obtained at a distance of roughly 4500 km from Ganymede's center.
Attached Image


I will probably post more Ganymede mosaics later this month or next month.
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nprev
post May 19 2007, 03:56 AM
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Bjorn, honored to be the first to complement you on this remarkable work! smile.gif

Interesting that Ganymede seems to have its own 'look' on this scale. The crater rims seem to be quite rounded, almost eroded in appearance...I'm at a loss to explain this, unless they are truly ancient and this is the result of micrometeoroid action over the ages as we see on the Moon. However, this conflicts with the existence of very prominent fracture/faulting features...odd indeed.


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edstrick
post May 19 2007, 08:51 AM
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One of the things that seems to happen on Ganymede and even more so on Callisto is the sublimation of ice by "dirty" regolith. Icy dirt gets hot enough in the afternoon to sublimate ice and darken itself. That accelerates the process. At the same time it can tend to creap downslope, tending to thin and expose more ice on elevations and slopes, lightening those surfaces and slowing the ice evaporation process. That seems to be very important in the highest resolution images, from what I've read (and also speculated myself). Callisto high-rez images show the resulting topography best.
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tedstryk
post May 19 2007, 03:49 PM
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Great work! It really is amazing how many good Galileo mosaics/images never became public release products. Here is one from G-2 (use the link for a higher resolution version).

http://www.strykfoto.org/g2-1a.jpg



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ElkGroveDan
post May 19 2007, 04:26 PM
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Thank you Bjorn. That was a real treat.

Too bad it's such a cliche now, but the term "alien landscape" would be most appropriate here.


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Bjorn Jonsson
post May 20 2007, 01:58 AM
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QUOTE (tedstryk @ May 19 2007, 03:49 PM) *
Great work! It really is amazing how many good Galileo mosaics/images never became public release products. Here is one from G-2 (use the link for a higher resolution version).

From the G2GSPLMPST01 imaging sequence it seems.

QUOTE (nprev @ May 19 2007, 03:56 AM) *
Interesting that Ganymede seems to have its own 'look' on this scale. The crater rims seem to be quite rounded, almost eroded in appearance...

I have noticed this too. Sublimation is probably significant. However, in some cases the very high contrast between the bright and dark material plays tricks on one's eyes and makes the relief appear greater than it really is.

Finally, here's a new one. This is a mosaic of 16 images from the Ganymede 2 G2GSLTDKBD01 imaging sequence obtained on September 6, 1996. The images show an area at ~61N, ~170W and were obtained at a distance of ~4300 km from Ganymede's center. North is up and a bit to the left. Many of the images were heavily compressed aboard the spacecraft (several by a factor of more than 20) so compression artifacts are clearly visible. This also significantly reduces the resolution (by a factor of roughly 2-4). This is also apparent in Ted's mosaic above.

Attached Image
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nprev
post May 20 2007, 05:38 AM
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Wow! huh.gif Thanks yet again, Bjorn! smile.gif

Temperature-dependent selective erosion aside as Ed correctly mentioned...this is odd. The 'hummocks' clearly are more recent than the craters, and actually seem to be destroying them over geologically recent time scales. Ganymede seems to be far more active than I thought....


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Exploitcorporati...
post May 20 2007, 09:40 AM
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Can't help but toss my hat in the ring with this obscure observation from the E12 orbit in December 1997. Galileo passed within 20,000km of Ganymede and took this hard-to-decipher oblique pan across the floor of the giant Gilgamesh basin. The fractures scale all the way down to the limit of resolution in the right-hand portion of the mosaic.

Attached Image


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edstrick
post May 20 2007, 09:43 AM
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Apparently we're seeing similar temp controlled sublimation at Iapetus and Hyperion. There's very un-intuitive feedbacks going on in the processes, I suspect, and quick-and-dirty arm-waving analysis can only go so far. These terrains will look *STRANGE* when we finally get some hard lander down on these objects. The fractured and faulted ice terrains of Europa and volcanic terrains of Io (not the S02/Sulfer etched terrains and the like) will look positively familiar, I suspect.
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MarcF
post May 20 2007, 12:15 PM
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Thanks a lot to all of you for these great mosaics !
These pictures were taken 10 years ago, and there is still a lot to do with them.
Did anybody try to assemble the very high resolution pictures taken during G1 over Xibalba Sulcus ?
Due to their "bad" quality, it might be difficult. I even don't know if they really overlap !
I also did not find any mention about the G29 images.
What about the regional and color polar cap boundary mosaic near Perrine Regio ?
Finally, there were these pictures taken when Ganymede was in Jupiter shadow in order to look for aurora events :
http://pdsimg.jpl.nasa.gov/outdir/4846r.img.gif
I never heard about them in any publication.

As you can see, my "frustration" is still quiet high ten years later, and that's why I really enjoy your posts.

Marc.
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tedstryk
post May 20 2007, 06:57 PM
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Well, I have this color mosaic I put together a few years ago from G29. I will say that because I made it years ago, I used relatively crude methods compared with what I use now, but at any rate, here it is.

Attached Image


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volcanopele
post May 20 2007, 07:02 PM
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smile.gif I might as well join the fray too:

Both of these are from a non-targeted encounter during orbit C9.



C9GSSULCUS01
Distance to planet center: 84379 km
This four-image mosaic covers portions of Xibalba Sulcus (roughly N-S set of grooves and ridges at the center of the mosaic) and Nineveh Sulcus (the roughly E-W set of grooves and ridges on the right-hand side of mosaic). This mosaic is roughly centered near 28 N, 82 W. Xibalba Sulcus seperates Galileo Regio on the left and Perrine Regio on the right.


C9GSGLOBAL01
Distance to planet center: 201468 km
This seven-image global mosaic is centered on Ganymede's leading hemisphere, with Galileo Region on the limb at upper left, Perrine Regio near the terminator at upper right. The bright ray crater Cisti can be seen near the bottom.


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tedstryk
post May 20 2007, 09:01 PM
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Here is a montage of Galileo Callisto and Ganymede views I did. I could swear I have a version of the Ganymede image somewhere without the horribly saturated whites, but I am not sure (it was a victim of my crash a few years ago, but I could swear it was backed up). In both cases, the color data is filled in from other orbits and Voyager.

Click the link for full resolution (keep in mind that full resolution is keyed to the Callisto image, which is much smaller).

http://www.strykfoto.org/calgan.jpg



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ElkGroveDan
post May 20 2007, 11:16 PM
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QUOTE (tedstryk @ May 20 2007, 10:57 AM) *
I will say that because I made it years ago, I used relatively crude methods compared with what I use now


Me too. Since the advent of Photoshop I have saved a fortune on tape and razor blades. You can hardly see the scars on my fingertips any more.


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tedstryk
post May 21 2007, 03:11 AM
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I have now completed my earlier post with an improved Ganymede and added Europa and Io.

http://www.strykfoto.org/calgalileans.jpg



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