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
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.
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.
Cassini looked toward the night sides of Enceladus and Saturn, catching Enceladus crossing the barely lit edge of Saturn's disk, to capture this unusual four-image animation on August 13, 2010.
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