Ashfall series (Pittacus Lore)

"Syd Chambers grew up on Earth with his human mother and barely remembers his alien father from Denza, who left on a mission when Syd was very young. After leaving Earth, Syd learned the truth of his father’s disappearance on the planet Ashfall—his father had died protecting a devastating secret about the history between humans and Denzans. Syd is now faced with a choice—free humanity from imprisonment on Earth, which will allow them to come...