The major component of Neptune's atmosphere is hydrogen (H2), making up about 80% of its atmosphere.

Here's the breakdown of Neptune's atmospheric composition:

* Hydrogen (H2): ~80%

* Helium (He): ~19%

* Methane (CH4): ~1.5%

While methane is a relatively small component, it plays a crucial role in giving Neptune its blue color. Methane absorbs red light, reflecting back blue light, which is why the planet appears blue to our eyes.