Mapping of Mercury

Mariner 10's mission came within 500 miles of Mercury's surface, provided a detailed mapping ofthe planet, confirming its rotation rate, temperature, and lack of significant atmosphere, and also detecting a faint magnetic field.
 (NASA) United States 1974 Mapping of Mercury

Mariner 10's mission came within 500 miles of Mercury's surface, provided a detailed mapping ofthe planet, confirming its rotation rate, temperature, and lack of significant atmosphere, and also detecting a faint magnetic field.