Ganymede Flyby - PJ35 Options

[Steve G]

In the earlier posts of the extended mission, there was listed a second Ganymede flyby at a more distant 50,000 km, also for mid 2021. Is this still happening, and what kind of science can we expect?

[tolis]

I think that flyby is happening tomorrow July 20th. Whether there are any science observations scheduled to take place is another matter.

[TrappistPlanets]

would we be able to image more night shine than?
it would be interesting what that tashmetum looks like up close

[JRehling]

would we be able to image more night shine than?
it would be interesting what that tashmetum looks like up close

FYI, we have had global maps of Ganymede at better than 31 km/pixel for decades now. We're not seeing it for the first time.

https://astrogeology.usgs.gov/maps/ganymede...-global-mosaics

New images may present a unique phase angle or simply be pretty, but if you're deeply curious about what Ganymede looks like up close, the good news is, that data is already here.

[mcaplinger]

Ganymede is only about 120 pixels across at this distance in Junocam images. We're taking some, but they're not going to be comparable to PJ34's images.

[MarcF]

Whar about JIRAM ? Anybody knows what kind of data have been taken and when some get public ?

[TrappistPlanets]

Whar about JIRAM ? Anybody knows what kind of data have been taken and when some get public ?

yeah, i am wandering where the images are, and why there was no news about it like there was during flyby 1
was it like forgotten or something...
like by now there should already be at least 1 images released
because the flyby times (during noon (or afternoon) were very similar
so i assumed we also should receive transmissions at around the same time too?

[Bjorn Jonsson]

Patience, patience. Also you cannot assume that the data downlink times are identical (or even very similar) to the PJ34 times. The same is true for the image release times. Also this Ganymede flyby isn't of any particular interest, unlike PJ34. As mentioned earlier, all of this terrain has been covered at much higher resolution by earlier spacecraft.

[TrappistPlanets]

my friend antdoghalo found the flyby 2 data on Mission Juno


i compiled 3 images from that image strip above
to get


i added the above to my Juno Ganymede (2021 data only) mosaic

[Brian Swift]

I see PJ35 has two TDI=16 Exposure=51.2ms images of Ganymede (PJ35_02 and PJ35_10).
I wonder what those are trying to observe (geysers, atmosphere, something else)?

[mcaplinger]

I see PJ35 has two TDI=16 Exposure=51.2ms images of Ganymede (PJ35_02 and PJ35_10).
I wonder what those are trying to observe (geysers, atmosphere, something else)?

Jupitershine? We were just trying it out since we had the available data volume.

[Phil Stooke]

Here is the Jupitershine greatly exaggerated. The near-terminator area is brightened as well.

Phil

[TrappistPlanets]

Here is the Jupitershine greatly exaggerated. The near-terminator area is brightened as well.

Phil

wow, how did you pull that jupitershine from the images
i tried myself, and kept failing

[JRehling]

I love the jupitershine result, Phil. Playing around with it in Photoshop, I find that if I gaussian blur it with a radius of about 8 pixels, then crank up the brightness, I can see some details that match up with existing maps – a couple of small rayed craters and the brightening to the northeast of Melotte Regio. (Melotte Regio is the name of the darker region in this image; from the way maps are labelled, it seems that the official boundaries may extend east of the place where my eye thinks it should; the boundary between darker and lighter terrain here is fragmented and it's a judgment call as to where one might put a boundary.)

I'd say that the sharpening you used here produces artifacts in the jupitershine areas and that by blurring it (or downsampling) by about 8x, and cranking up the signal about 64x eliminates the artifacts. Alternately, an exposure about 64 times longer might have given us sharp detail in the night areas, but that presupposes that such an exposure would have been practical, which is likely not the case. In general, low exposure brings to mind techniques that one uses in astrophotography of dim deep sky objects, which we usually don't have to think about with solar system images taken with sunlight.

[Phil Stooke]

Of course you are right about the atrocious artifacts. I had to do such terrible violence to the images to see the night side that nothing in that area is a real feature. It's only the limb that is significant.

Phil