The word that comes to mind immediately when first viewing this picture was scale. The size of everything feels flawless with how the space shuttles were scaled to the planets. It really helps the viewer be able to imagine this place actually existing. Another strong point of the picture is the different lines used through out to help keep the eye flowing through the picture without getting stuck anywhere. The ring around the planet, the trail from the space shuttles, and even the bright rims of light around the planet all help lead the eyes of the viewer around.
The color palate choice of this piece is also very well chosen. De-saturating and rewashing with a light tint of violet across the entire picture as you did was an extremely good choice. The faint aroma of violet really helps bring the planets to life.
Compositionally the picture is well planned. However I have to wonder if the picture would look better without the closest large planet. Having four spheres in such a skinny picture makes it feel a little cluttered, and I feel as if some of the sense of depth may be lost by having the close large planet.
Finally the texture and lighting that was used for the picture is exceptional. Be the texture self made or borrowed, it is a good choice, and used very well. The planets have a "real life" feel and look to them. The lighting is consistent throughout and helps create the great sense of depth, which also helps creating the vast sense of scale this picture has.
All in all the picture is well done, the craftsmanship is exceptional, and effort can clearly be seen throughout the entire piece. Keep up the great work.
Its all photoshop. Usually for planets I take various images from satllites that NASA use and stitch them together then alter colors and paint features on then to give a deired effect. The rest is ALL photoshop filters and effects