What is the smallest planet in our solar system?

The smallest planet in our solar system is Mercury. It is also the planet closest to the Sun, orbiting at an average distance of about 58 million kilometres. Mercury is a rocky, terrestrial planet with a heavily cratered surface that resembles Earth’s Moon.

Mercury’s equatorial diameter is about 4,880 kilometres, making it smaller than every other planet. It is even smaller in diameter than Jupiter’s moon Ganymede and Saturn’s moon Titan, although Mercury is more massive than either moon. Pluto is smaller than Mercury, but Pluto is classified as a dwarf planet rather than one of the eight planets.

Mercury is often confused with Venus because Venus is also a rocky inner planet and is sometimes visible near sunrise or sunset. Venus, however, is much larger. Mercury has a very thin exosphere, extreme temperature differences between day and night, and a year lasting only 88 Earth days. Despite being nearest to the Sun, it is not the hottest planet; Venus is hotter because its thick atmosphere traps heat so effectively.