Image credit: NASA
On 14 November 1971, the NASA Mariner 9 became the first spacecraft to orbit a planet other than Earth!
The Mariner 9 was launched on 30 May 1971.
Image credit: PD-USGov-Military-Air Force
Its 2 missions were to build on the atmospheric research gathered by the Mariner 6 & 7 missions and to map out the planet's surface.
On arrival, scientists found that a massive storm was raging on Mars' surface, something that continued for the next couple of months.
NASA computer engineers were able to delay the image reconnaissance until mid-January 1972, after the dust had settled.
The Mars 2 & 3 probes, which also arrived during that storm weren't able to remotely update the software, resulting in a limited supply of valuable data.
From January to October 1972 Mariner 9 orbited Mars at 1,500 km altitude. It sent back 7329 images back to Earth, covering about 85% of Mars' surface.
This detailed mapping resulted in a number of big discoveries: the existence of the high-altitude volcanos in the Tharsis plateau like Olympus Mons, extensive canyon network and evidence of wind and water erosion.
Olympus Mons is the tallest planetary mountain in the Solar System over 21 km or almost 70k feet.
Here is a picture that Mariner 9 took on 27 November 1971:
Image Credit: NASA/JPL
At first it was thought to be Olympus Mons, but later study showed that the volcano in the picture above actually is Ascraeus Mons, the 18 kilometer, second tallest mountain on Mars.
Not a lot of Mars' surface is visible because of the dust storms. This gives an idea of the scales of the dust storms.
Another discover was a canyon system of over 3,000 km. It became known as the Valles Marineris, in honor of Mariner 9.
You can see the massive valley in the middle of the image below, which was taken by a later Viking mission.
Image credit: Viking, USGS, NASA