Goals: Mariner 6 was designed to study the surface and atmosphere of Mars during a close flyby.

Accomplishments: The spacecraft transmitted 49 far- and 26 near-encounter images, showing heavily cratered and chaotic areas similar to parts of Earth's moon, and a southern polar region with an intriguingly irregular border. Spectrometry of the polar cap indicated solid carbon dioxide. Surface pressure was calculated to be equal to about 30.5 km above Earth's surface. Atmospheric composition was found to be about 98 percent carbon dioxide (at the time of Mariner 4's flyby, it was assumed to be mostly nitrogen). Nighttime surface temperature was recorded as -73°C at the equator, dropping to -125°C at the south pole.