Not everything that we see in the sky is a natural object. The Earth is surrounded by thousands of artifical satellites, and the bits and pieces left behind by launching those satellites. Sometimes it can be tricky to tell the difference between asteroids and satellites, at least with a single image. Once multiple images are available, it becomes possible to determine the orbit, which usually clears up any ambiguity.
See also my report on the CONTOUR Mission, and ill-fated probe intended to study several comets.
Click on images to enlarge.