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

Eros and Itokawa at similar scales

Itokawa looks very different from other asteroids that have been visited by spacecraft because of its gravel-covered surface and lack of craters. However, its different appearance may be partially to do with the different scales at which we typically look at different asteroids. Here are two pictures taken at a similar scale -- about 2.4 centimeters per pixel -- of Itokawa (top) and Eros (bottom). Both show gravelly surfaces. (Itokawa has other areas that are smoother, with finer gravel, like Eros does.) Although the two still look different, they are not as different as a direct comparison between whole-asteroid images would suggest.

Filed under pretty pictures, scale comparisons, asteroids, asteroid 25143 Itokawa, asteroid 433 Eros, Hayabusa (MUSES-C), geology

Enceladus, plumes, and rings

A crescent Enceladus sits below Saturn's rings in this photo taken by Cassini on January 4, 2012. The plumes have been artificially brightened to make them visible.

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

Moon Shadow Blocked by Ring

Another example of a moon shadow disappearing from view, i.e. blocked by a dense ring from penetrating to the side of the rings being viewed.

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

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Planetary Facts

Mass, diameter, density, gravity, orbital characteristics, presented both in metric units and measured relative to Earth.

Eros' northern hemisphere as seen by the NEAR spacecraft on February 29, 2000. The view is a mosaic of six images.

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.