Unlock Martian:
Press Right, Left, Right, Up, Down, Left, Right, Up, Up at the main menu.
Unlock Mars track:
Pause the game, then press Left, Left, Right, Right, Left, Left, Right, Right, Down, Left, Right.
Widescreen:
Pause the game, then press Left, Left, Left, Right, Right, Right, Up, Up, Up, Down, Down, Down, Left, Left, Left, Right, Right, Right.