I have been looking for a book I saw a while back, and for the life of me cannot remember the title, or author. I haven't read the book, its relatively new (post 2010 by approximation).
Focal point is this: Something happened to the sun (expansion being my guess) and it has swallowed earth. The humans, predicting this event, moved to Mars to avoid the initial subsumation of the earth. Now the sun continues to expand to the point it will destroy Mars. Mars wasn't a long-term destination anyway, so they continue onwards. The main character is some scientists' kid who stayed with his parents as the 'rearguard'.