Simplify the following text for a Grade 8 native English-speaking person.
Original: On February 10 , 1975 , the US Post Office issued a commemorative stamp featuring the Mariner 10 space probe .
Simplified: Mariner 10 was a robotic space probe launched on November 3 , 1973 , to fly by the planets Mercury and Venus . Mariner 10 is no longer functional today but is still orbiting the sun .