The outer planets atmosphere is made up of hydrogen and helium. Because they are so large their gravitational force is very powerful.
The outer planets all have rings (although not as visible as Saturn's.) All of the outer planets have more than one moon (except for Pluto but Pluto is considered a dwarf planet). Most of the outer planets are Gas Giants (except Pluto, again).
Pluto was considered a planet until 2006, then it was reclassified as a dwarf planet. Pluto's ellipse is the weirdest of them all. It has an elongated and tilted ellipse that is completely unique. It takes 248 earth years to orbit the sun. It is also the coldest planet with a record winter of -235 degrees Celsius.
The most inreresting part of the outer planets are their atmospheres, temperature, and their elipse. They are the coldest planets, the longest orbital time, and the gassiest atmosphere.
