8h 6min, may 30, 1971 y - Mariner 9
Successful Mars orbiter (NASA)
Mariner 9 was the first spacecraft to go into orbit around another planet. However, excitement for its arrival was subdued by a dark cloud -- literally. A Martian dust storm, which had started in late September 1971, had grown to cover the entire planet. When Mariner 9 arrived in November, the only surface features visible were the summit of Olympus Mons and the three volcanoes of Tharsis Ridge. Mission scientists had to wait about a month and a half until the dust settled before they could begin the science portion of the mission. When the spacecraft ran out of fuel almost a year later (on October 27, 1972), Mariner 9 had taken a total of 7,329 images of Mars, studied the atmospheric and surface composition of the planet, the density and pressure of its atmosphere as well as the planet's gravity and topography. The spacecraft also provided scientists with the first close-up views of Phobos and Deimos, the two moons of Mars.
Added to timeline:
the videos are in the parts of Mars Exploration Rover Spirit...