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

Sibling Worlds

Can you tell which is Earth and which is Mars? On the left, images from the Red Planet as captured by the Opportunity rover and the Mars Reconnaissance Orbiter. On the right, locations of roughly the same scale in and around Canyonlands National Park, Utah. Click the image for a longer caption and more details.

Filed under pretty pictures, many worlds, amateur image processing, Earth, Mars, Mars Exploration Rovers, Opportunity, Mars Reconnaissance Orbiter, Earth analogs, geology

Io eclipses and transits Ganymede

On August 16, 2009, amateur astronomer Christopher Go captured this fourteen-frame animation on two of Jupiter's moons. You can see smaller Io's shadow cross Ganymede just before the moon itself transits.

Filed under pretty pictures, animation, many worlds, amateur astrophotos, Jupiter's moons, Io, Ganymede

Io and Europa

Io (upper right) and Europa, photographed by the New Horizons spacecraft in 2007. Io displays three of the volcanic plumes that help to supply its atmosphere, including the giant Tvashtar plume near the north pole.

Filed under pretty pictures, global views, many worlds, Jupiter's moons, Io, Europa, New Horizons

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Planetary Facts

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

Eros' northern hemisphere as seen by the NEAR spacecraft on February 29, 2000. The view is a mosaic of six images.

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.