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On This Day in History - July 14, 1965

Mariner 4 space probe. Credit: NASA

The Mariner 4 space probe was one of a series of ten space probes designed to gather information about the planets within our Solar System, most specifically Earth's closest neighbor Mars. The Mariner 4 mission was the seventh attempt to send a spacecraft to Mars. Between 1960 and 1964 the Soviet Union had tried and failed five times. NASA launched Mariner 3, also intended for Mars, four weeks before Mariner 4 but it failed to separate from the Atlas-Agena rocket upon lift off. Mariner 4 was launched from Cape Canaveral, Florida, on November 28, 1964 carrying technical instruments including a magnetometer, dust detector, cosmic ray telescope, trapped radiation detector, solar plasma probe, Geiger counter and, most importantly, a television camera.

Technicians working on the Mariner 4 before launch. Credit: NASA

After traveling for 228 days Mariner 4 flew within 10,000 km of Mars, and on July 14, 1965 captured the first images of another planet ever taken in space. The images were radioed back to Earth as digital data. Mariner 4 could transmit information through its high-gain antenna at a speed of 33.3 bits per second and its low-gain antenna at 8.3 bits per second. Sending a whole image (200 by 200 pixels) took about 10 hours. Over a few hours Mariner 4 took a grand total of 21 complete pictures of Mars. With each photo covering an area of about 200 square km, the fuzzy black and white images collectively captured just 1% of the Martian surface.

Various collages of images taken by Mariner 4 on July 14, 1965. Credit: NASA

Mariner 4’s mission put an end to centuries of fantasies about Mars. It showed the Red Planet to be a battered, crater-pocked world, more like the Moon than Earth, with no signs of water or other necessary conditions for life. It also collected data about the planet crucial to the success of subsequent exploration missions. One of the most important observations was the unexpected finding that Mars has very low atmospheric pressure, a fraction of what is found on Earth. Scientists thus knew that successfully landing a module on the surface would require retro rockets as well as parachutes.

Mariner 4 continues to be regarded as one of NASA’s most successful missions, well worth its estimated $83 million cost. After its Mars flyby, the spacecraft coasted into solar orbit, continuing to return data to Earth for another three years. Final contact was lost on December 21, 1967.”

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