Mercury size and scale context

Mercury is the smallest planet in the Solar System and the closest one to the Sun. Because of its unusual spin-orbit rhythm, one Mercury solar day lasts 176 Earth days, which is longer than its 88-day year. Read its scale context, comparisons, and journey links on the canonical object page.

CallistoGalilean moon·4,821 km

MercuryTerrestrial planet·4,879 km

TitanLarge icy moon·5,150 km

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Moons

Callisto

Callisto is Jupiter's second-largest moon and the outermost of the four Galilean moons. Its ancient, heavily cratered surface records a quieter history than Io, Europa, and Ganymede, while Galileo spacecraft data suggest a possible salty ocean deep below the ice.

Scale fact4,821 kmdiameter

Object class: Galilean moon
Mass: ~0.018 Earth masses
Host: Jupiter
Estimated age: ~4.5 billion years
Composition: Rock and water ice

Planets

Mercury

Scale fact4,879 kmdiameter

Object class: Terrestrial planet
Mass: ~0.055 Earth masses
Host: Sun
Estimated age: ~4.5 billion years
Composition: Metal-rich silicate rock
Temperature: ~440 K mean surface

Moons

Titan

Titan is Saturn's largest moon and the only moon in the Solar System with a dense atmosphere. Its methane weather cycle feeds clouds, rain, rivers, lakes, and seas, making it one of the most world-like places beyond Earth.

Scale fact5,150 kmdiameter

Object class: Large icy moon
Mass: ~0.023 Earth masses
Host: Saturn
Estimated age: ~4.5 billion years
Composition: Water ice, silicate rock, nitrogen-methane atmosphere
Temperature: ~94 K surface