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
During its first long orbit of Jupiter, Juno used its JunoCam to capture images of Jupiter and its moons two to four times per hour. From July 10 to July 16, 2016, as Juno receded, it took two frames per hour, with two 7-hour gaps on July 14. From July 16 to July 28, it took four frames per hour, so the animation appears to slow down. From July 29 to August 27, it took two frames per hour. The animation continues until just two hours before Juno's closest approach.
Juno took this expansive view of Jupiter with two of its moons on August 26, 2016, on approach to its August 27 perijove. Juno was about a million kilometers away from Jupiter at the time. Both moons are farther away from Juno than Jupiter is. Europa is at left, Io at right.
Juno captured this view of Jupiter with its innermost large moon Io on approach to its first orbital periapsis, on August 27, 2016. Juno was about 630,000 kilometers from Jupiter at the time.
An asteroid or comet headed for Earth is the only large-scale natural disaster we can prevent. Working together to fund our Shoemaker NEO Grants for astronomers, we can help save the world.