And as for Earth's Moon, I wonder if they could search for Surveyor 4, which some say crashed just seconds after losing contact with Earth right before landing in 1967, while others think it may have landed fine but just could never relay any data to Earth.

An orbiting camera might solve that mystery - and certainly another lander. We could also justify it on scientific grounds, as Surveyor 4 obviously never got to relay back any data about the landing site.

As for the Soviet Mars landers of the early 1970s, Mars 2 and 6 need to be found to see if they did indeed crash or had something else happen to end their missions prematurely. As for Mars 3, perhaps we could learn why it stopped transmitting so abruptly, and if its little tethered rover did its job despite being unable to call home.