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Compare the Planets

Comparing the physical characteristics of the worlds in our solar system (and beyond)

The worlds of our solar system come in all shapes, sizes, and colors. Red-eyed Jupiter, ringed Saturn, and frigid Uranus and Neptune are giant gassy globes containing nearly all of the matter in the solar system. These Jovian planets, or gas giants, are huge worlds of air, clouds, and fluid that may have no solid surfaces no matter how deep you go. Everything else in the solar system is just rock, ice, and dust. The largest rockballs are known as the terrestrial planets: Mercury, Venus, Earth, and Mars, with our Moon usually considered part of the club, and now Vesta is applying for membership. Earth is the biggest of all the rocky worlds.

But the planets are not the only worlds of the solar system. All but two of the planets are orbited by moons, each of them a world unto itself. The largest moons are bigger than the smallest planets, and 16 or 17 would qualify as dwarf planets if they orbited the Sun. There are more than 100 Kuiper belt dwarf planets, but only one among the asteroids, Ceres.

Six solid worlds -- Venus, Earth, Mars, Titan, Triton, and Pluto -- have atmospheres dense enough to produce weather. Eris likely does, when it is near its perihelion. We have witnessed active geology on four worlds -- Earth, Io, Enceladus, and Triton -- and we suspect it on Venus, Europa, and Titan. Comparing the same processes across many worlds helps us to understand how each planet's unique composition and history influence its present state, and will help us predict what to expect on Earth in the future.

Pretty Pictures with Many Worlds

Pluto and its Moons

Pluto and its Moons

Pluto, Charon, Nix, and Hydra, as observed by the Hubble Space Telescope on February 15, 2006.

Filed under trans-neptunian objects, Hubble Space Telescope, pretty pictures, Pluto, Charon, Eris, many worlds

Interiors of icy bodies in the solar system (as of 2010)

Interiors of icy bodies in the solar system (as of 2010)

Many bodies in our solar system may contain oceans. Jupiter's ice-coated moons (Europa, Ganymede, and Callisto) probably contain internal saltwater oceans. The more distant large and medium-sized icy moons, the icy dwarf planets, and tiny Enceladus may contain colder ammonia-water oceans. Oceans in icy satellites could be a common feature throughout the universe, while Earth's surface ocean may be the more unusual case. These interior models were developed by many geophysicists from data about the sizes, densities, and orbital characteristics of each body. Credit:

Filed under Enceladus, Titan, Rhea, dwarf planets beyond Neptune, Saturn's moons, Jupiter's moons, trans-neptunian objects, Pluto, pretty pictures, scale comparisons, Charon, Eris, Triton, Neptune's moons, Uranus' moons

Three worlds

Three worlds

On March 11, 2014, Stuart Atkinson caught this view of three planetary wanderers in the sky over Kendal, Cumbria, England: Mars, Vesta, and Ceres.

Filed under asteroid 4 Vesta, pretty pictures, asteroids, Dawn, Earth, Mars, stars and galaxies, many worlds, asteroid 1 Ceres, amateur astronomers

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Section Highlights

Planetary Facts

Mass, diameter, density, gravity, orbital characteristics, presented both in metric units and measured relative to Earth.

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Asteroids and Comets Visited by Spacecraft

A comparison of all the asteroids and comets ever visited by spacecraft, up to date as of November 10 (when Deep Impact flew past Hartley 2). Vesta is not included.

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Every Round Object in the Solar System, to Scale

A correctly scaled, reasonably correctly colored view of the largest bodies in the solar system.

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Space in Images

Pretty pictures and
awe-inspiring science.

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