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Juno Perijove 22, September 12, 2019
mcaplinger
post Sep 13 2019, 12:37 AM
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Images have started appearing on missionjuno.


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Disclaimer: This post is based on public information only. Any opinions are my own.
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Kevin Gill
post Sep 13 2019, 03:55 AM
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Thanks for letting us know!

First composite image using the PJ22 data

JNCE_2019255_22C00017_V01
JNCE_2019255_22C00018_V01
JNCE_2019255_22C00019_V01
JNCE_2019255_22C00020_V01
JNCE_2019255_22C00021_V01
JNCE_2019255_22C00022_V01

Reprojected to the perspective of '22.



Jupiter - Fisheye Composite - Perijove 22
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Kevin Gill
post Sep 13 2019, 11:41 PM
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Shadow of Io starts appearing in PJ22-25!


Jupiter - Shadow of Io - PJ22-26
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fredk
post Sep 14 2019, 01:13 AM
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Spectacular - very cool how the projection from close up makes Io's shadow look crazy big.
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Explorer1
post Sep 14 2019, 01:27 AM
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Reminds me of a classic science fiction movie involving Jupiter...
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Bjorn Jonsson
post Sep 14 2019, 03:21 PM
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Approximately true color/contrast detail from image PJ22_26 showing Io's shadow:

Attached Image


This image is enlarged by a factor of 2 compared to the original data. This makes Jupiter's bluish sky at the limb more obvious.
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fredk
post Sep 14 2019, 06:28 PM
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Stunning, Bjorn. I always appreciate the attempt at true colour.

I suppose you've done some masking of the sky - the pixel values are zero in the sky, but small though nonzero in the shadow, as a gamma-tweak illustrates:
Attached Image

Is that just a nonzero black level in the shadow? Another idea would be real scattered illumination from the illuminated atmosphere outside the shadow, or illumination from partially sunlit moons (other than Io). Both those seem unlikely.
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fredk
post Sep 14 2019, 07:52 PM
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A related point: knowing the geometry we should be able to plot the edge of the umbra on the image, and then measure how much scattered light is visible inside the umbra - perhaps interesting from the atmospheric science point of view?
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mcaplinger
post Sep 14 2019, 08:55 PM
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QUOTE (fredk @ Sep 14 2019, 10:28 AM) *
Is that just a nonzero black level in the shadow?

I don't see any signal in the shadow in the raw images that is any brighter than the stray light from the instrument.

Stay tuned, the later images show the shadow even better.


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Kevin Gill
post Sep 14 2019, 11:58 PM
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Two more composite views:



Perijove 22 - Composite - #3


Perijove 22 - Composite
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JohnVV
post Sep 15 2019, 05:22 AM
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QUOTE (Kevin Gill @ Sep 13 2019, 07:41 PM) *
Shadow of Io starts appearing in PJ22-25!


Jupiter - Shadow of Io - PJ22-26



for those fallowing this using Celestia , there is a spice ssc file on Celestialmatters
http://forum.celestialmatters.org/viewtopi...start=15#p15441

and some screen shots
http://forum.celestialmatters.org/viewtopi...start=15#p15437
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JRehling
post Sep 15 2019, 08:03 AM
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I have distorted the image to circularize the shadow, and I don't see any obvious Io plumes, but then the noise of Jupiter's variation makes that a difficult search.

If there is any discernible movement of Io's shadow while ≥2 images were made of it, then it would be possible to divide an image of its penumbra by the same area of Jupiter in sunlight and search for relatively faint plume shadows.
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Bjorn Jonsson
post Sep 16 2019, 10:53 PM
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QUOTE (fredk @ Sep 14 2019, 06:28 PM) *
Stunning, Bjorn. I always appreciate the attempt at true colour.

I suppose you've done some masking of the sky - the pixel values are zero in the sky, but small though nonzero in the shadow, as a gamma-tweak illustrates:

Yes, I did some feathered masking in Photoshop near the limb. Otherwise I'd get a sharp, unrealistic cutoff in the dark (but not totally black) area a bit outside of Jupiter's limb. This is because I reprojected the raw framelets to simple cylindrical projection and added 200 km to Jupiter's radius when reprojecting to avoid losing Jupiter's sky (which usually happens if I use the cloudtop radius value).

QUOTE (fredk @ Sep 14 2019, 07:52 PM) *
A related point: knowing the geometry we should be able to plot the edge of the umbra on the image, and then measure how much scattered light is visible inside the umbra - perhaps interesting from the atmospheric science point of view?

This would be difficult because the shadow contains stray light from the instrument as pointed out in an earlier post. This scattered light varies in non-trivial fashion depending on the viewing geometry, the sun direction etc. I haven't attempted to model these effects and correct for them.

However, if memory serves there are some Galileo images where a big satellite shadow is visible. These images might have less stray light and/or be easier to calibrate if measurements of the umbra brightness are desired - I suspect compression artifacts in the Galileo images might make this impossible to measure properly though.
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Bjorn Jonsson
post Sep 16 2019, 11:17 PM
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This is processed from image PJ22_23. Approximately true color/contrast and enhanced versions:

Attached Image
Attached Image
Attached Image


Attached Image

Attached Image
Attached Image
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JRehling
post Sep 17 2019, 03:05 AM
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HST images might have less of a stray light issue than Juno or Galileo, and resolve the moon shadows fairly well?

https://hubblesite.org/contents/news-releas...ws-2015-05.html

In all cases, I guess an operational constraint in measuring the brightness inside an umbra would be image depth. If you're calibrated to show the surface of Jupiter, I would guess that the brightness in the center of a moon shadow would be far below the quantum of sensitivity. Eg, JunoCam images are returned at 8 bits, so < 1/256 is essentially zero?

FWIW, when Io, Europa, or Ganymede is casting a shadow on Jupiter, the other two of that trio must either be on the far side of Jupiter or present as a razor-thin crescent. Callisto, however, is potentially a spoiler, and a crescent/gibbous Callisto could potentially be shining onto the scene.
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