US Spacecraft 1st visited Mercury on this day
'Mariner 10' became the first spacecraft to visit the planet Mercury on March 29, 1974. It was an unmanned US space probe, launched by NASA in November 1973. Further, Mariner 10 is the only spacecraft to have visited Mercury till date. It flew past Mercury three times; second time on September 21, 1974 and third time on March 16, 1975.