The Mars of Malcontents - The Slums of the Solar System, #2

Valentina knows how to live in the community spread throughout the old mining caves under the Martian ice cap. A violent place in a forbidding climate, but home for her and her brother. Until she wakes from a coma to find her brother gone. Her father thinks her incapable of following them back to the equatorial cities. He underestimates her - her stubbornness, her courage and her inventiveness. But she underestimates the cold, airless surface of Mars.
A journey from the polar ice cap to the Martian equator? Not enough to stop Valentina. Not with her brother on the line.