After the movie release and in spite of its failure, three books came out to tell the events which followed the destruction of Earth during 15 years :

• Cale story
• Akima story
• Sam story
Unfortunately, I didn't find anything about the novel Sam story, its existence is only told on Wikipedia article and nowhere else.

Cale story

- where did he go after Earth ?
- when has he got his tatoo ?
- what does it mean ?
- did the Drejs destroy other planets ?
- how did he arrive on Tau 14 and why ?

Cale was 5 when the Drej destroyed Earth. This day, he saw his father, Sam, for the last time, who has escaped the catastrophe. Aboard of the Titan - a dramatic spaceship. He grown up with Tek, an alien friend of Sam, and almost has all forgotten about his homeworld and keeps only one memory of Sam : a ring which does not have to leave his finger. But he has to give it to Klegg, a bad guy who threats to kill Iji, Tek's daughter. Cale will have to take it back ! Because this ring is the key of the mystery that depends the Humanity's future ! ...

Akima story

- where did she go after Earth ?
- what do mean her hair style and her hair color ?
- how has she learn to fly ?
- why is she hopefull ?
- how did she met Korso ?

Akima is a castaway. She has escaped Earth few hours before that the Drejs destroyed it, she grown up - too fast - in one of the drifter colonies where live the humans. His only hope, and the one of all humans, it's the Titan, a spaceship which could give back hope and future to Humanity. To find it, Akima is agree to sacrify her youngles and risk her life. After learn to fly, she leaves the colony and goes on a quest of all dangers...