The world of dirt!
Used: photoshop elements 9

how does it hold together?

The same way as the sun?
But nah it's actually solid, with the top surface cracking.

The world of dirt because it's dirty/dusty.

That's really cool, I like the style of it. Looks like some sort of concept art for a movie.

Planets have enough gravity around them to pull things in and make them orbit around them or even collide with them. The density of the planets are also so condensed that it makes a perfectly circle. Hence every planet in the solar system is round. Now this could pass as a non-planet, but not a planet etc. I would suggest making it perfectly round, or making it easier, would be make a clear hemisphere around it (Of course not totally transparent, but something that would kind of glow on the outsides ect. Now that outline of the planet below it(Just assuming it is) That can be a planet and the main focus can be a comet/moon or something.

Seing that stuff is falling off the surface I'd say that you'd need a ring of dirt orbiting the planet. Due to the fact that huge chunks of the surface are going so far from the ...uh surface

Or, the planet had a quite wet surface, but due to global warming in the long run the planet lost its atmosphere as the conditions were totally screwed, and as such water have since evaporated, leaving the top crust to dry and hence shatter into fragments.

I dig this very much. Really love the concept and feel of the whole composition

What he said! Its what earth will probably end up like in 100 years

Good job, Roo.
Although the suggestion of the dust ring could really spice up your piece.

I also find the galaxy in the background a bit boring and bland,
the planet with the light coming over it in the bottom could use a lot of work, too.

I'm missing a red, a green and a yellowish tint.
That with the other suggestions and you'll have an even better painting ;]

Keep up the good work, buddy.