The first is a planet. It was created from a foam ball I bought in a crafts store, with a piece of wire coat hanger punched through it to act as a support. The ball was painted with watered down wood glue prior to spraw painting to prevent the spray paint from melting the foam. Once the basecoat was painted on and dry, I simply drybrushed bands of color around the circumferance of the sphere at varying heights to create a swirling gas-giant effect.
The other three pieces are gas clouds. They are made from MDF/hardboard cut into irregular shapes. Their edges were smoothed with a hand sander, and then they were spray painted black. The gas cloud effect was created simply by dry brushing a dark color onto the board (purple and blue in this case). Then, additional drybrushes were performed with lighter shades of the base color, moving closer and closer to the center of the cloud. I used a streciling brush, as the large flat end of the brush allowed for a good combination of drybrushing and stipling. After the cloud was completed stars of varying size were painted on using white paint and a fine brush.