Pause the game and press Left (3x), Right (3x), Up (3x), Down (3x), Left (3x), Right (3x).

Unlock Martian

While at the Main Menu, press Right, Left, Right, Up, Down, Left, Right, Up, Up.

Unlock Mars Tracks

Pause the game and press Left, Left, Right, Right, Left, Left, Right, Right, Down, Left, Right.