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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

Earth and the Moon from Chang'e 5 T1

Earth and the Moon from Chang'e 5 T1

The Chang'e 5 test vehicle service module took this photo of Earth and the Moon together on November 9, a week after successfully returning the sample capsule. The Moon's surface is quite dark compared to Earth's bright clouds.

Filed under pics of Earth by planetary missions, pretty pictures, Earth, the Moon, Chang'E program, many worlds

Comet Siding Spring after its close approach to Mars (Rolando Ligustri)

Comet Siding Spring after its close approach to Mars (Rolando Ligustri)

Comet Siding Spring (just above center) and Mars (brilliant object to lower left) seen on October 20, 2014 at 09:47 UT, hours after the comet's closest approach. Image acquired from iTelescope Siding Spring, Australia. The bright star at upper right is 51 Ophiuchi.

Filed under pretty pictures, comets, amateur astrophotos, comet Siding Spring, Mars, many worlds

Comet Siding Spring just hours before its close approach to Mars (Damian Peach)

Comet Siding Spring just hours before its close approach to Mars (Damian Peach)

Less than eight hours from closest approach, Siding Spring's green coma is dwarfed by the brilliant blaze of Mars.

Filed under pretty pictures, comets, amateur astrophotos, comet Siding Spring, Mars, many worlds

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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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Space in Images

Pretty pictures and
awe-inspiring science.

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