After using the gravity of the larger planet Venus to fling it further toward the sun, NASA’s unmanned space probe Mariner 10 zips by the innermost planet, Mercury, less than 500 miles away from its cratered surface. Its cameras capture the first-ever views of the barren planet, whose surface temperatures vary between frigid on the night side and oven-baked on the hemisphere facing the sun. Mariner 10 passes behind the sun, catching up with Mercury again half a year later.
