There's a few dozen nuclear powered RORSATS. When their start leaking (due to micrometeorite strikes or just wear & tear), they leak out globs of coolant that coagulate together. Each satellite has a few hundred points of coolant, which can make a LOT of 1cm across globs (or larger globs, or droplets that are too small to detect). I don't have a paper handy, but IIRC these droplets were the #1 source of space junk up until the 2007 antisatellite weapon test

e: Paper here, https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.27...