Early planetary probes showed the planets to be largely boring places. Mariner 4 showed Martian craters and no canals or vegetation. Venus didn’t show us a darn thing. In fact the first probe, Mariner 2, didn’t even carry a camera or other imaging device.
Mariner 10 snapped some mostly unremarkable images in the mid-70’s from its three fly-bys of Mercury. “Just like the moon,” some said.
Earlier this month, Messenger’s imaging systems showed lots of those craters again, yes, but some subtle differences and a few surprises. Today’s mission status report is here. And here’s an image of what the mission scientists have nicknamed “the Spider.”
Nothing on the moon is like this network of graben features.