all the that builds up in the atomosperethe gases head in one direct motion and the reason y terrestrial planets r closer to the sun is bcuz of the heat that comes from the sun
They are so large travelling closer to the sun they would have an increased velocity losing there gas to solar winds ect.
http://funadvice.com/r/15dmnodmqcj
The planets closer to the sun are more dense because the sun is nearer to it and for the gas planets, they are far away so they aren't as dense.
the suns heat evaporates the gasses