Lost in the glare following the Apollo 11 Moon landing, two intrepid robotic spacecraft flew by Mars in the summer of 1969 and returned photographs and a trove of scientific information.
Launched on February 25 and March 27, respectively, Mariner 6 and 7 arrived at Mars just five days apart despite being launched a month apart. After a flight of 156 days from Earth, Mariner 6 flew within 2,132 miles of Mars on July 31, roughly twice as close as Mariner 4’s flyby in 1965. Controllers lost contact with Mariner 7 for seven hours just five days before its planned flyby, but by August 2, after quick replanning, they restored the spacecraft to full capability as it began its encounter with Mars. Three days later, it passed within 2,130 miles of Mars’ southern hemisphere. Both spacecraft flew behind the planet and a radio occultation experiment measured the surface pressure of the Martian atmosphere to be between 6 and 7 mb, or less than 10% of Earth’s atmosphere at sea level. After their successfully flybys, Mariner 6 and 7 sailed on into solar orbit.