These objects provide functionality for manipulating data from the Mariner missions. From 1962 to 1973, ten planetary spacecraft were launched under the name Mariner, targeting our neighbors, the inner planets Mercury, Venus, and Mars. There were six missions, most missions launching a pair of Mariner spacecrafts a few months apart. Of the ten launched Magellan spacecrafts, seven were successful in their missions, and three were lost due to launch vehicle failures.

USGS Astrogeology: http://astrogeology.usgs.gov/Missions/Mariner/