1971 Planet-Encircling Dust Storm

The 1971 global dust storm was the first planet-encircling storm observed from orbit by NASA's Mariner 9 and the Soviet Mars 2/3 orbiters. When Mariner 9 arrived on November 13, 1971, it found the entire Martian disk obscured; only the summits of Olympus Mons and the three Tharsis Montes protruded above the dust. Mariner 9's controllers placed the spacecraft in a holding orbit for roughly three months before the atmosphere cleared sufficiently for systematic mapping to begin. The storm almost certainly contributed to the 20-second failure of the Mars 3 lander on December 2, 1971.