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
There are four moons in the solar system that are known to have collisional atmospheres. In order of decreasing atmospheric column density, they are: Saturn's Titan, Neptune's Triton, and Jupiter's Io and Callisto.
On March 25, 2015, the Cassini spacecraft captured three of Saturn's moons in the same shot. From left to right: Rhea, Titan, and Mimas. (Mimas is barely visible below and to the right of Titan.)
A montage of 17 of the 18 asteroids and comets that have been photographed up close as of August 2014, when Rosetta arrived at comet Churyumov-Gerasimenko. This version is in color and shows the bodies at their correct relative (though not absolute) albedo or brightness. Not included are Vesta or Ceres, both of which are many times larger than Lutetia.
Filed under Venus missions before 2000, comet Wild 2, scale comparisons, amateur image processing, comet Churyumov-Gerasimenko, comet Halley, comet Hartley 2, comet Tempel 1, asteroid 433 Eros, comet Borrelly, asteroid 4 Vesta, asteroid 2867 Steins, asteroid 25143 Itokawa, asteroid 253 Mathilde, Galileo, asteroid 243 Ida and Dactyl, asteroid 21 Lutetia, asteroid 4179 Toutatis, asteroid 951 Gaspra, Rosetta and Philae, Hayabusa (MUSES-C), pretty pictures, comets, Deep Impact, Stardust, asteroids, NEAR
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