Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object, co-developed between NASA and NSTA, is the second of four Science Objects in the Solar System SciPack. It explores the similarities and differences in the planets that make up our solar system. Each planet moves around the Sun in the same direction in a nearly circular orbit, though each planet has its own unique orbital period and speed. The planets vary in size, surface and atmospheric composition, and surface features. In orbit around the planets, we find a great variety of moons, flat rings of rock and ice debris, and/or artificial satellites. Features of many of the planets and their moons show evidence of formation and evolutionary processes similar to those that occur on Earth. These processes include earthquakes, lava flows, erosion, and changes in the atmosphere.