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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

Rhea on the rings with Prometheus and Janus

Rhea on the rings with Prometheus and Janus

Cassini was nearly two million kilometers away from Rhea on March 28, 2010 when it captured this approximately natural color view of the moon sitting in front of Saturn's rings. In the background are two much smaller moons, Prometheus (sitting in front of the F ring on the left) and Janus (above the rings to the right).

Filed under pretty pictures, Cassini, amateur image processing, Rhea, Saturn's small moons, Saturn's moons, many worlds, Saturn, Saturn's rings

The Pluto system on May 15, 2005

The Pluto system on May 15, 2005

This and another photo from the Hubble Space Telescope have revealed that Pluto has two more, small moons in addition to the previously known Charon.

Filed under Hubble Space Telescope, pretty pictures, Pluto, Charon, many worlds, Pluto's small moons

Jupiter and Ganymede from Hubble

Jupiter and Ganymede from Hubble

On April 9, 2007, Hubble caught Ganymede in the act of setting behind Jupiter. Ganymede is the largest moon in the solar system, bigger than the planet Mercury.

Filed under Jupiter's moons, Hubble Space Telescope, pretty pictures, Ganymede, many worlds, Jupiter

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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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