The outer planets, also known as the gas giants, are primarily composed of hydrogen (H) and helium (He). These elements make up the vast majority of their atmospheres and interiors.

Here's a breakdown of the gases found in each outer planet:

* Jupiter:

* Hydrogen (H): Approximately 89.8%

* Helium (He): Approximately 10.2%

* Trace amounts: Methane (CH4), ammonia (NH3), water (H2O), and other compounds.

* Saturn:

* Hydrogen (H): Approximately 96.3%

* Helium (He): Approximately 3.25%

* Trace amounts: Methane (CH4), ammonia (NH3), water (H2O), and other compounds.

* Uranus:

* Hydrogen (H): Approximately 82.5%

* Helium (He): Approximately 15.2%

* Methane (CH4): Approximately 2.3%

* Trace amounts: Water (H2O), ammonia (NH3), and hydrogen sulfide (H2S).

* Neptune:

* Hydrogen (H): Approximately 80%

* Helium (He): Approximately 19%

* Methane (CH4): Approximately 1.5%

* Trace amounts: Water (H2O), ammonia (NH3), and hydrogen sulfide (H2S).

It's important to note that while these planets are primarily composed of hydrogen and helium, they have different atmospheric compositions due to the presence of other trace gases. These trace gases contribute to the unique colors and atmospheric features observed on each planet.