MarsMariner 4 successfully passes by Mars at a distance of just over 6,000 miles, and transmits the first direct measurements of the Martian environment to Earth, along with the first pictures ever taken of another planet from a nearby spacecraft. Mariner 4’s onboard instruments detect a thin atmosphere – thin enough that any future landing attempts will need to descend on retro rockets, but thick enough that a heat shield is still necessary. These findings have a ripple effect on NASA’s plans for a robotic Mars lander. After its flyby of Mars, Mariner 4 continues on into deep space.

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