Oisín,
I’m not familiar with that book, but looking up the author I see that she has written 200 books, which seem to be straightforward non-fiction.
https://www.rebeccarissman.com/
I like how you have planned to link science to the creative process with designing Martians for a landscape. I would discuss with the children what is like on Mars quite explicitly – which I would hope the book would provide the details.
One common misconception that I encounter is that children think Mars is hot!