Soft brushes draw back to everyone's style. Do yourself a favor and don't attempt this yet. It's 100x more complicated than you think.
Trust me, I have 19 of his psd's, and I've looked through each of them layer by layer.
Each of his many shapes in his "balls", so to speak, has a purpose that is rooted in an element of art. You might know how to make the shapes and how to organize them into a sphere, because that's entirely mechanical. But until you know why that color is there and this color is here, yours will just look like a jumble of random colors, shapes, and lines.
I was more distracted by the drop shadow behind the planet...
Or that lol. I dont know, I find it odd he has shining light coming from a corner of the planet, like there is a bright star behind the planet. Meanwhile to the left of it, there is already another light source.