this looks cool! I recently did a version of this scene myself...ironically enough I had Morgoth with a sort of Space background too...you should check out my gallery and see. though, my art leans towards a comic-bookish style. as where yours here puts me more in mind of the Peter Pracownick LOTR, and thats awesome!
Melkor had the ability to change his form. when he first entered Arda he looked horrible and was huge, but the later when he was overthrown by the valar for the first time and brought to Mandos' halls he changed his form to betray the others and "since in that time all his words and works were fair, and he became in outward form and seeming even as the Valar his brethren, Manwe gave him his freedom within Valinor" (J. R. R. Tolkien: Morgoth’s Ring. Part Two: The Annals of Aman.)
I think the artist wanted to depict the beautiful melkor^^ Besides, this picture is rather abstract, which I like
Hmm, an intriguing rendition. I like how pensive he looks, not just generically evil. And how his body seems to be put together out of crystals - a nice reminder that the Valar choose their body shape and form. I have a question - is this picture portraying Melkor in Mandos as the title says, or in the Void as the artist's description suggests?