Mercury has the shortest year of any planet in the Solar System, orbiting the Sun in about 88 Earth days.
Mercury is the innermost planet, with an average distance of about 58 million kilometres from the Sun. Its close orbit means it travels at an average speed of roughly 47 kilometres per second. A Mercury year lasts 87.97 Earth days, although the planet rotates slowly compared with its orbital motion.
Mercury's solar day—the interval from one sunrise to the next—lasts about 176 Earth days. This happens because Mercury completes three rotations for every two orbits, a relationship called a 3:2 spin-orbit resonance. Its surface experiences extreme temperature changes because it has almost no atmosphere to retain heat.
Venus is the next planet outward and has a longer 224.7-day year. Mercury should not be confused with the hottest planet: Venus is hotter overall because its dense carbon-dioxide atmosphere creates a powerful greenhouse effect.