Mariner 7, following Mariner 6's flyby on July
31, has its closest approach at a distance of 3,524 kilometers (2,190
miles). This mission is the first dual mission to a planet.
By chance, both craft fly over cratered regions and miss both the
giant northern volcanoes and the equatorial grand canyon that are
discovered later. Their approach pictures do, however, show that
the dark features on the surface long seen from Earth are not canals,
as once interpreted in the 1800s.