Jupiter 03.07 and unidentified shadow

[riklaunim]

I've been playing with capturing/processing Jupiter at f/20 and f/15. The images aren't super good, but I noticed I got a "shadow" on the planet, but I can't see any moon that could cast it - both Io and Calisto on the left, "sunny" side are emerging from beneath Jupiter not transiting in front of him - so what is making the shadow that is on f/20 and f/15 shots?

f/20:

mysterious shadow:

f/15:

DMK21 with filter threaded focal reducer and shor nosepiece - all moons:

[DarkerSky]

Nice images.

The shadow isn't a moon as far as im aware - although I think Io's shadow was going across the disk earlier.

The shadow is in the EZ - not somewhere you would normally see a dark spot.

You could have something there !

CM of system I at your obs time was 85 degrees approx.

Could be good to see if it is still there when that CM comes round again, or if it has changed

[riklaunim]

I've noticed that there is something white and rather round before the dark spot: http://i48.tinypic.com/2czeb9t.jpg

So it can be a small moon or flyby of something. F/20 big image was stacked from bit underexposed frames to freeze the seeing better so overexposed image isn't likely.