In the past half-century, mankind has lifted itself from the surface of its world and thrown messages into the black of space. Space is big - impossibly so - and our spacecraft pass in the night without even knowing it.
Sometimes, though, these little packages from Earth get a chance to see each other. These are those pictures - those little waves across the void.
(This is not a full catalogue of such images - primarily because the Mars Reconnaissance Orbiter seems to delight in taking ultra-long-distance shots of various landers, most of which don't look all that different from each other)