First off, this request sounds more like a demand than a friendly "Hey can you do this for me".
Firstly; 1600x1200 to fit into a 600x150 space without warping it = impossible
Secondly; Even when fitting it into 600x150 the small planet doesn't appear unless you reduce the height of the image = which warps the shape of the planets.
Thirdly; Even when you've warped the shape of the planets to fit 600x150 = there isn't enough space now at the top of the image to write anything along the top of the larger planet.
At least those are the issues I've been confrunted with after 10 seconds of experimentation.