NASA’s unmanned space probe Mariner 10 makes its second pass of the planet Mercury, six months after its first flyby. This time Mariner passes under the planet’s south pole, getting the first views of that part of Mercury, but barely flying within 30,000 miles of the surface. Once again, following its encounter with Mercury, Mariner 10 slipped into a solar orbit that would bring it back to Mercury several months later.
