The solar system consists of the Sun and objects that orbit it, including 8 planets. Mercury is the smallest planet and closest to the Sun. Venus has the densest atmosphere. Earth is the only planet known to harbor life due to its oceans. Mars has a reddish surface from iron oxide dust. Jupiter is the largest planet, over 2.5 times more massive than all others combined. Saturn has rings and is the second largest planet. Uranus and Neptune are icy giants on the outer edges of the solar system.