Genesis Earth by Joe Vasicek

Michael Anderson never thought he would set foot on an Earthlike world. Born on the farthest edge of the solar system, he studies planets from afar. But when his parents open a wormhole and discover signs of intelligent life on the other side, Michael is the only planetologist young enough to voyage to the alien star.

He is not alone, but Terra, his sole mission partner, is no more of an adult than he is. Soon after their arrival, she begins keeping secrets from him. But she doesn’t realize that her darkest secret is one that he already knows.

Twenty light-years away from humanity, what they discover on the alien world forces them to question their deepest beliefs about the universe—and about what it means to be human.