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
Cassini captured the three images for this approximately true color composite on October 18, 2010. While Cassini studied Titan, the mid-sized icy moon Dione wandered through the field of view, while Prometheus sat atop the F ring at upper left.
Phobos passes through the Super-Resolution Channel field of view on Mars Express' High-Resolution Stereo Camera on the spacecraft's orbit 7982 (March 26, 2010). Levels in the images have been adjusted to make Mars' surface appear roughly similar from frame to frame in the background. Phobos is significantly darker than Mars.
Titan as seen by Cassini on June 22, 2010, and Pluto as seen by New Horizons on July 14, 2015. Both worlds are viewed from a phase angle of 165 degrees -- nearly from behind. Both have atmospheres; particles in the atmospheres scatter sunlight forward toward New Horizons, lighting them up. The observing spacecraft are seeing the skies in all the locations where the Sun is rising or setting on the surface. The Pluto image has been downsized to match the scale of the Titan image.
Our Advocacy Program provides each Society member a voice in the process.
Funding is critical. The more we have, the more effective we can be, translating into more missions, more science, and more exploration.