The solar system is centered around the sun and includes planets, dwarf planets, asteroids, and comets. Mercury is the planet closest to the sun, Venus is the hottest planet with dense carbon dioxide atmosphere, and Earth orbits the sun once every 365.25 days. Mars is often called the red planet due to its red-colored surface. Jupiter is the largest planet and Saturn has prominent rings composed of rocks and ice. Uranus and Neptune are gas giants farther from the sun. Pluto is a dwarf planet beyond Neptune's orbit.