The scale of Neptune is 49,244 km which is almost 4 times the size of our planet, Earth. Earths diameter is 12,756 km. Do you know what Neptunes structure is? The structure of Neptune is made up of ammonia clouds, ammonium hydrosulfide clouds, water clouds, liquid layers and water drops. Do you know what Earths structure is? There is the crust, the core and the mantle. Neptune is 4.503 billion years old! Do you know how old the universe is? The universe is 14 billion years old! Earth is a lot younger then that, it is 4.543 billion years!