Final answer:
Knowledge about Mercury primarily comes from space missions, particularly the Mariner 10 and MESSENGER spacecrafts which provided detailed photographs and mapped the planet's surface.
Step-by-step explanation:
Almost all we know about Mercury has come from space missions that have sent spacecrafts to study the planet closely. The Mariner 10 spacecraft, which passed within 9500 kilometers of Mercury's surface in 1974, was the first to provide a close-up look, returning over 2000 images with details as fine as 150 meters. Later on, the MESSENGER mission gave us a comprehensive mapping of the planet after it orbited Mercury in 2011 until it concluded its mission in 2015. Similar to astrological explorations of other planets, Mercury's study involves sending robotic explorers that have not only orbited but also flown past and crashed into the planet, transmitting valuable data back to Earth.