Flexi Says: Uranus and Neptune were discovered using a telescope. They are similar to each other in size and composition. They are called ice giants as these planets are composed mainly of hydrogen and helium. They are both smaller than Jupiter and Saturn, and also have more icy materials. These materials include water, ammonia, and methane. There is a thick layer of gas on the outside. Further on the inside is liquid gives them icy blue-green color.