Mariner 10The first unmanned space probe to use a gravity assist maneuver to get from one planet to another in a reduced amount of time, Mariner 10 is lauched on a course for the planet Venus, where a carefully planned trajectory allows it to take pictures and measurements at that planet before using Venus’ gravity to fling Mariner 10 inward toward Mercury, allowing it to reach two planets in under two months. It will be the first space probe to visit Mercury.