From NASA's Planetary Photojournal
Mariner 10's first image of Mercury acquired on March 24, 1974 from a distance of 3,340,000 miles (5,380,000 km) from the surface of Mercury. The diameter of Mercury (3,031 miles; 4,878 km) is about 1/3 that of Earth. During its flight, Mariner 10's trajectory brought it behind the lighted hemisphere of Mercury, where this image was taken, to acquire important measurements with other instruments. Mercury looks very similar to the Moon. But its higher gravity means that debris from impacts with the same energy are closer to the main impact (crater) than on the Moon.
Image Title: The Planet Mercury
Catalog #: PIA00437
Target Name: Mercury
Mission: Mariner 10
Last Modified On: Sunday, December 17, 2000