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
This animation contains 15 images captured between June 1 and 15. The images have been resized to account for the changing distance between New Horizons and the Pluto system during that time, which ranged from 50 to 35 million kilometers.
Faint stars in the background of raw images from New Horizons allow the images to be aligned, giving us a sense of New Horizons' changing view on Pluto and Charon as it approaches the dancing pair. Images were taken between June 1 and 15, 2015. More information in this blog entry.
This artist's illustration shows the scale and comparative brightness of Pluto's small satellites, as discovered by the Hubble Space Telescope over the past several years. Pluto's binary companion, Charon (discovered in 1978), is placed at the bottom for scale. Two of the moons are highly oblate. The reflectivity among the moons varies from dark charcoal to the brightness of white sand. Hubble cannot resolve surface features on the moons and so the cratered textures seen here are purely for illustration purposes.
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