Japan's MMX mission aims to solve the puzzle of Mars' moons

Japan's MMX space mission will study the origin of Mars' moons, Phobos and Deimos. Scientists weigh competing theories: captured asteroids versus debris from a giant impact on Mars.

• MMX mission will investigate the origin of Phobos and Deimos
• Earth's Moon formed after a collision over 4 billion years ago
• Mars moon theories include asteroid capture and impact debris