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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

The Moon transiting Earth as seen from Juno

The Moon transiting Earth as seen from Juno

These views of Earth and the Moon were captured by the Advanced Stellar Compass, or star tracker camera, on Juno as the spacecraft approached for its October 9 flyby of Earth. The sequence begins on October 6. The original images are monochrome; faint coloration has been added by converting the measured grayscale values into false colors matching a true color image of Earth.

Filed under pics of Earth by planetary missions, pretty pictures, Earth, the Moon, many worlds, Juno

Two crescents: New moon, old Venus

Two crescents: New moon, old Venus

A day-old Moon and a waning Venus crescent appeared very close to each other in the sunset sky on January 2, 2014 (left). Cutting out and comparing the two crescents to each other shows their similar illumination but dissimilar sizes (right). Venus, roughly four times the diameter of the Moon, was near inferior conjunction so about 50 million kilometers away (more than 100 times farther away than the Moon).

Filed under pretty pictures, amateur astrophotos, Venus, the Moon, many worlds, amateur astronomers

Enceladus and Rhea

Enceladus and Rhea

Cassini spotted Rhea passing behind Enceladus in this 20-frame animation from November 15, 2009.

Filed under Enceladus, pretty pictures, Cassini, amateur image processing, Rhea, global views, Saturn's moons, many worlds, animation

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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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