This view of the volcanic plains of Neptune's moon Triton was produced using topographic maps derived from the images acquired by NASA's Voyager spacecraft during its August 1989 flyby

Triton was the last solid object visited by NASA's Voyager 2 spacecraft as it headed toward the edges of our solar system.

Triton, Neptune's largest moon, is one of the "coolest" objects in the solar system, literally, with a surface temperature of minus 235 degrees Celsius (minus 391 degrees Fahrenheit). Voyager 2 discovered that Triton has active geysers.

The images and a movie show the moon's sparsely cratered surface with smooth volcanic plains, mounds and round pits formed by icy lava flows.
The Voyagers are the farthest human-made objects in the solar system.
Voyager 1 is 16.6 billion kilometers (10.3 billion miles) or about 111 Astronomical Units from the Sun. Voyager 2 is 13.5 billion kilometers
(8.4 billion miles) or about 90 Astronomical Units from the Sun. Both are expected to reach interstellar space in five to eight years (2014 - 2017).

More information on the Voyagers is available at: http://voyager.jpl.nasa.gov/index.html