Last Day on Mars (Chronicle of the Dark Star series)

Thirteen-year-olds Liam and Phoebe are the final human beings remaining on Mars. They uncover a scheme intended to wipe out humanity. Their discovery places two young people on Mars at the center of a threat to the entire human population. The book begins the Chronicle of the Dark Star series, and Liam and Phoebe are identified as its two central characters. Its premise combines their isolated location with the danger they uncover.