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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

Epimetheus and Janus

Epimetheus and Janus

Cassini captured this mutual event of Epimetheus and Janus on December 25, 2005, during Rev 19.

Filed under pretty pictures, Cassini, Saturn's small moons, global views, Saturn's moons, many worlds

Titan, Dione, rings, Prometheus

Titan, Dione, rings, Prometheus

Cassini captured the three images for this approximately true color composite on October 18, 2010. While Cassini studied Titan, the mid-sized icy moon Dione wandered through the field of view, while Prometheus sat atop the F ring at upper left.

Filed under Dione, pretty pictures, Cassini, Titan, amateur image processing, Saturn's small moons, global views, Saturn's moons, many worlds, Saturn's rings

Phobos from Mars Express HRSC SRC

Phobos from Mars Express HRSC SRC

Phobos passes through the Super-Resolution Channel field of view on Mars Express' High-Resolution Stereo Camera on the spacecraft's orbit 7982 (March 26, 2010). Levels in the images have been adjusted to make Mars' surface appear roughly similar from frame to frame in the background. Phobos is significantly darker than Mars.

Filed under pretty pictures, Mars Express, Mars, many worlds, Phobos

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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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