Mercury experiences the greatest temperature variations in the solar system. This is due to two factors: its proximity to the Sun and the almost total absence of an atmosphere to regulate heat. The side exposed to the Sun, where it is eternal day, can reach scorching temperatures of about 430°C, hot enough to melt lead. Meanwhile, the side plunged into eternal night sees temperatures drop to -180°C. No other planet has such a violent thermal contrast between its day and night sides.
Despite its equatorial furnace, a surprising discovery was made by the Messenger mission: the existence of water ice and other frozen organic materials in the craters at Mercury's poles. The bottoms of these craters, located at the North and South Poles, are permanently in the shadow of the Sun's rays. These cold traps act as cosmic freezers, preserving volatiles that would instantly vaporize elsewhere on the planet. This discovery makes Mercury a surprising member of the family of icy worlds.
Mercury's orbit is the most eccentric (most elongated) of all the planets in the solar system. Its distance from the Sun thus varies greatly, from 46 million kilometers at its closest (perihelion) to 70 million kilometers at its farthest (aphelion). This high eccentricity, combined with its slow rotation, creates a fascinating phenomenon: a 3:2 spin-orbit resonance. This means that the planet rotates three times on its axis for every two orbits around the Sun. As a result, a solar day on Mercury (from one sunrise to the next) lasts the equivalent of 176 Earth days, or twice as long as its year of 88 days.
Mercury never strays more than 27 degrees from the Sun (this is the angle of the clock hands when it is one o'clock). Learn more.
N.B.: The official definition of a planet (since 2006) requires that it orbits the Sun, has a spherical shape due to its own gravity, and has "cleared" its orbit.
ETNO, Relics of the Primordial Chaos: In Pursuit of the Ghost of Planet Nine 
Phantom Super-Earths: The Lost Worlds of the Solar System 
Perihelion and Aphelion: The Apsides in the Solar System 
Winds of the solar system and giant planets
3D Simulator: Revolutions of the Planets
Mercury: The Planet with Two Faces
Venus: Earth's Infernal Twin
Earth, the Blue Planet: A Fragile Jewel in the Universe
Mars: The Conquests and First Human Steps on the Red Planet
Jupiter: A Failed Star at the Heart of Our System
Saturn: The Harmony of Orbital Resonances
Uranus: The Planet Tipped on the Horizon of the Solar System
Neptune: The Blue Giant of the Solar System
Roche limit
Remarkable characteristics of the planet Mercury
Remarkable characteristics of the planet Venus
Remarkable features of planet Earth
Remarkable characteristics of the planet Mars
Remarkable characteristics of the planet Jupiter
Remarkable characteristics of the planet Saturn
Remarkable characteristics of the planet Uranus
Remarkable characteristics of the planet Neptune
Characteristics of Planets: What Makes Them Unique
Venus, Veiled Planet: A Puzzle in our Solar System
Live on Mars
The seven wonders of the World
Planet 9 is still nowhere in sight
Axial Tilt of Planets: An Unstable Dance Through the Ages
Comparative sizes of planets and stars
The Journey of the Planets Along the Ecliptic: A Cosmic Choreography
Declination and right ascension
Saturn's Rings: A Ring System in Jeopardy