That's not actually the manual exposure mode in planet mode. Manual exposure mode shows two sliders, one for shutter speed, and one for gain. For Jupiter in particular turn the gain down to 5 (no more, no less) and then tweak the shutter speed until you can see banding on Jupiter. You simply cannot get the exposure right using the default exposure mode even with the slider all the way to the left.
As for AF it's hard for the S50 (especially if in the city) to ever see the planet as anything other than a big fuzzy blob, until it changes the focus which will cause the blob to leave the focal plane, the exposure actually drops a little, and you get these sorta crisp lens flares which it thinks are sharper than the object it's trying to focus on, and it gets stuck with the focus far far from where it should be.
That's why.. the stars are relevant. It's easier just to shift the scope a little off the target, set the exposure for the stars, let it AF on the stars (which it will see as crisp little points) and then move it back to the planet and set the exposure as needed.
