Looks like taken with rather dim lighting, i.e. high-iso. In which case all these dots in the dark area could be explained as hot pixels (pixels that have a tiny bit of leakage that then shows up when massively amplified). Of course, that leakage might be due to comsic rays ;-) but the amount of them doesn't look worse than what you might get on earth (depening upon circumstances).

Also, with really long exposures, this leakage tends to add up, too.