This Globe Holds Some Of The First Detailed Photographs Of Mars

How do you organize photographs of an alien world in the era before computers? By printing them out and sticking them to a globe of the planet!

Mariner 6 (top two rows) and Mariner 7 (center to down right and south pole) pictures printed and assembled on a Mars globe on March 20, 1970. Image credit: JPL

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The Mariner flybys past Mars were our first up close and personal view of the red planet. After the quick glance of the planet provided by Mariner 4 in 1965, Mariner 6 and 7 arrived in 1969 for a more extensive survey of Mars.

Mars experienced its first dual flyby with the arrival of Mariner 6 and Mariner 7 in 1969. Image credit: NASA/JPL

Mariner 6 and Mariner 7 were a matched set of identical spacecraft, sent to fly past Mars as the first dual encounter with the planet in 1969. Mariner 6 made the first flyby with Mariner 7 tagging along just five days later. The experience of manoeuvring the first probe was used to improve instructions for the flyby for the second probe, programming the 11.8-kilogram Control Computer and Sequencer for autonomous control during the flyby.

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Artist’s concept of the Mariner 6 and 7 spacecraft. Image credit: NASA/JPL

They carried identical payloads with both near and far resolution cameras, infrared and ultraviolet spectrometers, an infrared radiometer, a celestial mechanics experiment, and an S-band occultation experiment.

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Both probes carried identical television cameras: Camera A, a wide-area lens covering 1,000 kilometers x 1,000 kilometers with a 3 kilometer resolution, and Camera B, a telephoto lens covering 100 kilometers x 100 kilometers with a 300 meter resolution. The cameras alternated taking pictures so a new photo was taken every 42 seconds. Mariner 6 sent home a total of 75 images during its flyby (49 far, 26 near) and Mariner 7 sent home another 126 images (93 far, 33 near), a massive improvement over the measly 21 images returned by Mariner 4 five years earlier. The probe pair sent home 800 million bits of data during the two flybys.

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Narrow angle images from Mariner 6. Image credit: NASA/JPL reprocessed by Ted Stryk

Fifty hours before closest approach to Mars on July 29th, 1969, Mariner 6 flipped on its scientific instruments and started scanning the planet. A cooling system failure knocked the infrared spectrometer out of service, but otherwise the mission succeeded as planned. Based on the mission findings, Mariner 7 was rerouted farther south than originally intended, prioritizing near-encounter photographs on the light side of the planet. In the global model of the planet, Mariner 6 took the two two rows of photographs, while photographs from Mariner 7 extend from the center to the bottom right and across the Martian pole.

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Global view of Mars as seen by Mariner 7 during its approach. Image credit: NASA/JPL

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While the photographs finally cleared up that the long dark features were not canals, both probes managed to find entirely cratered regions. Despite photographing 20% of the planet’s surface, both probes missed the epic volcanoes and canyons that fascinate us today. In addition, the probes identified a predominantly carbon dioxide atmosphere (98%!) with a surface pressure of 6 to 7 millibars, about the same as about 30.5 kilometers altitude on Earth. The probes also found a polar icecap composed of frozen carbon dioxide, and nocturnal surface temperatures as low as -73°C at the equator and -125°C at the south pole. The spacecraft also further refined estimates of the mass, radius, and shape of Mars.

When Mariner 9 arrived at Mars in 1972, they quickly acquired far too many images for this technique to work. Instead, Mariner 9 was all about the Mars mosaics. ...assembled the hard way by hand-trimming photographs with scissors.

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Read more about the Mariner 6 and Mariner 7 spacecraft or about early Martian image processing. Check out an interview with Don Davis, the airbrush artist who worked on the original Mariner Mars globes, here.

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