You have captured an image of a star-seed, giant interstellar creature that come in to star systems to give birth and then use the principle of solar sailing to escape. This one is getting an extra gravity boost from Jupiter
An Outsider ship is sure to follow. (Larry Niven's Known Space Universe).
Seriously now:
Some funky internal reflection. The rectangular shape suggests a reflection off the front glass window onto the back of the lens. Maybe even a double reflection or off the next lens element in as suggested by rectangle within rectangle. I expect rectangular part to be always diagonally opposite Jupiter across center.
The semi-circular swipe looks like a reflection off the barrel ...