Mercury

Mercury is Sun's first and closest planet to the Sun. he has the shortest orbit at 87.97 days, and he and Venus orbit closer than Earth. he probably is tidally locked with a 3:2 spin-orbit resonance. in his early days, he kept getting hurt by asteroid collisions just like the Moon. he is hot in the daytime and cold in the nighttime. he was visited by 2 spacecraft, Mariner 10 and MESSENGER.

Structure of him
he experienced that he his shrinking because his core is very big. he is smaller than Ganymede (one of Jupiter's moons) and Titan (one of Saturn's moons).

Orbit and Rotation
he has the most eccentric orbit out of all planets in the solar system.

he also has the 2nd longest rotation, first is Venus. his rotation lasts for 87.97 days

Him in fiction
he also appears in many works of science fiction.
 * in Collision Earth. a solar flare knocks him out of his orbit and crashes into Earth. killing him.
 * in Invader Zim. he was turned into a prototype station.
 * an episode of Futurama had his circumference into a "road sign" having the only road station on his surface when Fry and Amy are stuck and Amy's vehicle runs out of feul

Trivia

 * Mercury is home to many craters you can go on his template in Wikipedia.