Neptune

Weird things happened in the outer Solar System when it was first a'borning. The ice-giants, Uranus and Neptune, are the two outermost major planets of our Sun's family, and in size, bulk, composition, and great distance from our Star, they are very much alike. Both distant worlds are clearly different from the quartet of small rocky inner planets--Mercury, Venus, Earth, and Mars--as well as from the duo of gas-giant planets, Jupiter and Saturn. Ice giants are planets that contain elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. Although the two planets should be almost identical twins, they are not.…