Original: It was launched approximately 2 years after Mariner 9 and was the last spacecraft in the Mariner program ( Mariner 11 and 12 were purposed to the Voyager program and redesignated Voyager 1 and Voyager 2 ) .
Simplified: Mariner 10 was a robotic space probe launched on November 3 , 1973 , to fly by the planets Mercury and Venus .