This was a really good middle-grade read. Perhaps a little too in your face with the message at times, but I really enjoyed the story and I think it's a beneficial read for the target audience. 

What's funny to me is that this little book meant for children managed to scare me more than the horror novels I've read. The author relayed the emotions and what was happening so well that I couldn't help imagining myself in Petra's situation, and it was both terrifying and extremely emotional to the point I got choked up. I would have preferred more 

closure at the end and I was hoping for more time on the planet.

That would have elevated it to five stars for me.