Final answer:
Elijah is likely painting in the surrealist genre, as it involves imaginative and dream-like elements that are suitable for depicting an alien planet inspired by science fiction.
Step-by-step explanation:
Elijah is painting the surface of an alien planet that is one giant ocean, with inspiration from a science fiction novel. Considering the subject and inspiration, Elijah is most likely painting in the surrealist genre. Surrealism involves elements of surprise, unexpected juxtapositions, and non-sequitur. While some other genres like seascapes or landscapes focus on realistic depictions of natural scenery, surrealist artists often seek to express imaginative dreams and the subconscious, which aligns with the theme of an otherworldly oceanic planet. On the other hand, impressionist artists capture momentary atmospheric conditions and society scenes using pure color laid down in small touches that blend when viewed from a distance, which seems less relevant in this context of alien-inspired creativity.