Hammerhead (Mars Diaries)

The Earth scientists call it a killer comet. Headed toward Mars, it threatens to destroy the dome and all who live in it. Their only chance is Tyce Sanders, who must learn to pilot a test space vehicle in only a matter of weeks. As the crisis worsens, Tyce discovers the comet is the least of the problems on Mars. And that the secrets and betrayals will test the strength of his new faith.