caption: <PERSON>, following <PERSON>'s flyby on July 31, had its closest approach at a distance of 3,524 kilometers, in what was the first dual mission to a planet. By chance, both craft flew over cratered regions and missed both the giant northern volcanoes and the equatorial grand canyon that were discovered by <PERSON>. Their approach pictures did, however, show that the dark surface features long seen from Earth were not canals, as once thought in the 1800s.
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