A dust storm that began on 22 September 1971 in the Noachis region eventually encircled the planet. When Mariner 9 arrived in November Olympus Mons and the three Tharsis volcanoes were the only features visible above the haze. By 30 December 1971 the orbit had been adjusted to have a periapsis of 1650 km and orbital period to 11:59:28 hr so that synchronous data transmissions could be made to the Goldstone 64-m DSN antenna. The dust storm had abated by then and the Mariner 9 spacecraft operated until 27 October 1972 when the attitude control gas was depleted.
Mariner 9 mapped 70% of the Martian surface and obtained views of Deimos and Phobos. It provided data to begin our understanding of temporal variability of the surface and atmosphere of the planet.