Date: 24 Mar 1974
This is Mariner 10's first image of the planet Mercury. It was acquired on 24 March 1974. During its flight, Mariner 10's trajectory brought it behind the lighted hemisphere of Mercury, where this image was taken, in order to acquire important measurements with other instruments.
This picture was acquired from a distance of 5,380,000 km (3,340,000 miles) from the surface of Mercury. The diameter of Mercury (4,878 km; 3,031 miles) is about 1/3 that of the Earth.
Images of Mercury were acquired in two steps, an inbound leg (images acquired before passing into Mercury's shadow) and an outbound leg (after exiting from Mercury's shadow). More than 2,300 useful images of Mercury were taken, both moderate resolution (3-20 km/pixel) color and high resolution (better than 1 km/pixel) black and white coverage.