Juno Perijove 49, March 1, 2023 Options

[volcanopele]

I'm going to choose to be optimistic about PJ49, so with that in mind, I have added previews of JunoCAM's observations of Io for PJ49. Obviously, JunoCAM's real observation plan will likely differ but I added previews for the first and last opportunities to image Io on the pass, a preview of an image nearest closest approach, and one for when Io is near the center of the JIRAM FOV. The observation at closest approach also has the Marduk plume which has a good chance of being observed on this encounter, presuming it is active. The Volund plume might also be visible near the terminator.

The previews use the Voyager/Galileo basemap. The left images were originally projected at the same resolution as JunoCAM but were then enlarged by 5x while the image on the right is the basemap reprojected to 5x the JunoCAM pixel scale.

https://pirlwww.lpl.arizona.edu/~perry/Juno/pj49.htm

[Bjorn Jonsson]

In the PJ48 images, the reddening trend of the JunoCam images greatly accelerated (see the PJ48 thread). Interestingly, the reddening in the PJ49 images apparently has reverted back to the trend before PJ48. The PJ49 images actually seem to be *less* red than the PJ49 images. There are some sources of errors and uncertainty (in particular few images at PJ48 and no northern hemisphere PJ48 images) but this seems pretty certain nevertheless. Below is an updated plot showing the color correction factors I'm currently using for every perijove.



This is different from a plot I uploaded back in 2021. There I was measuring the blue/red ratio in raw images with no processing except for decompanding. Here I am interested in the color correction necessary after decompanding, flat fielding and dark current correction. Actually the flat fielding and dark current correction results in only a tiny change to the blue/red ratio (or in this case the color correction). The color correction is in % with e.g. 275 for blue meaning that I multiply blue with 2.75.

Here the measured multiplier for blue is 4.5934 at PJ48 and 4.3315 at PJ49. These values are averages from several different measurements. Even if I selected the lowest values I got for PJ48 and the highest values I got for PJ49, the PJ49 images are less red (these values are 4.55 for PJ48 and 4.42 for PJ49). In the image above, the PJ48 value is abnormal enough that I didn't include it when computing the Bezier curve.

It is very interesting that this increase in red relative to blue occurred following a JunoCam anomaly at PJ48. Maybe it is even more interesting that the PJ49 images are less red than the PJ48 images; this is very unusual as the graph above shows.

In addition to what's discussed above the data above suggests the following:

(1) The reddening probably didn't start until sometime after PJ20 (possibly at PJ22 or PJ23).
(2) This reddening trend probably accelerated near or following PJ40 (it is not clear exactly when but the trend when looking at several PJs around PJ40 suggests this).

[StargazeInWonder]

Very interesting, Bjorn.

Your comments on the further anomalous details of the reddening (eg, the effect being greater in PJ48 than in PJ 49), as evidenced on the blue line, seem also to appear, to a lesser extent, on the green line. One might try to verify this statistically, and narrow the number of degrees of freedom at work.

This is probably grasping at straws, but I wonder if there is any additional feature in any of the images that might constrain the source of the effect. Eg, do Saturn, Earth, Sirius, etc. ever appear as a background object that could measure the effect on another known reference object? Given that Ganymede was too small to serve in that capacity, I guess anything outside the Jupiter system would also be hopeless in this regard. Io, on the other hand, has now appeared in multiple PJ imagery, but has its own remarkable variations in color that might disqualify it for the purpose, unless the same terrain has appeared several times.