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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

Prometheus and Pandora herd the F ring (movie)

Prometheus and Pandora herd the F ring (movie)

This movie sequence from Cassini shows dark drapes in the inner strands of Saturn's F ring caused by the gravitational influence of the shepherd moon Prometheus. Prometheus appears first in the sequence, interior to the F ring, and Pandora follows along outside of the ring. Prometheus orbits closer to Saturn, and thus faster, than the icy particles that make up the F ring. The moon passes closest to the ring at "apoapse", when it is farthest from Saturn. It is during these apoapse passages that Prometheus has its greatest influence on the fine ring material. With time, the ring material previously affected falls behind so that on the next apoapse passage of Prometheus, a new gore in the inner ring material is made. The material closer to Prometheus orbits the planet faster than the material closer to the bright F ring core. The gores, together with the sheared-out material, create the dark, diagonal drapes. Visit the Planetary Photojournal to download a high-resolution, 170-frame version of this movie.

Filed under pretty pictures, Cassini, Saturn's small moons, Saturn's moons, many worlds, animation, Saturn's rings

Galileo's best images of Thebe, Amalthea, and Metis

Galileo's best images of Thebe, Amalthea, and Metis

On January 4, 2000, near its orbit periapsis, Galileo captured its highest-resolution images of three of Jupiter's four inner regular moons: Thebe, Amalthea, and Metis, imaged from 192,700; 237,700; and 292,600 kilometers away, respectively. The images have been enlarged from their original resolution to a common scale for comparison, and rotated to place north approximately up. Thebe is about 84 kilometers pole-to-pole; Amalthea, 128 kilometers; and Metis, 38 kilometers.

Filed under Jupiter's moons, pretty pictures, scale comparisons, Galileo, Jupiter's small moons

Atlas, Prometheus, Epimetheus, and Janus dancing near the rings

Atlas, Prometheus, Epimetheus, and Janus dancing near the rings

This animation is composed of 22 frames captured through Cassini's narrow-angle camera on July 27, 2010 at around 2:15 UTC. Four of the ring-moons cross through the field of view during the animation.

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

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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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