A new study attempts to uncover the origins of the Martian moons, Phobos and Deimos, which have been a mystery to scientists for many years. Two groups of researchers claim that Mars’ moons were the result of a giant collision in the planet’s early history.

The study published on July 4 in the journal Nature Geoscience cites that a study by a team of French, Belgian and Japanese researchers demonstrated that Mars’ moons were the debris of a collision between Mars and a protoplanet one-third its size. This event occurred about 100 to 800 million years after the Red Planet’s birth.

The debris from the collision formed a very wide disk around the planet.  The inner part of the ring was made of matter in fusion while the outer ring was made of a thin layer of gas.

The inner part formed a moon a thousand times bigger than Phobos but has disappeared over time. The gravitational interaction between the outer gas layer and a star resulted in the formation of smaller moons later on.

Only 10 small moons and one big moon were left surrounding Mars after a few thousand years. However, when the debris disk disintegrated a few million years later, the planet’s tidal effects brought these moons, including the big one, down into its surface. Only Phobos and Deimos were left.

However, researchers from  the French National Centre for Scientific Research (CNRS) and Aix-Marseille Université disagree that most of the moons came back down to Mars. They say that the light signature produced by the two present satellites is not similar to the one found on Mars.

Still, they agree that Mars’ moons were formed by a collision between Mars and another object. Moreover, they believe that the moons were made of dust formed by gas condensation in the outer disk. Each dust particle measured less than a micrometer.

The giant collision may also be the reason behind the difference in altitudes between Mars’ northern and southern hemispheres, which have lower and higher altitude, respectively.

The Borealis basin in the planet’s northern hemisphere is also most likely the remains of the collision.  The Martian slow rotational velocity, about six times slower than Earth, could have also influenced the creation of Mars’ moons instead of only one moon like ours.

The researchers admit that further research is still required to determine the truth behind this mystery. Nevertheless, we may unlock the secret in several years as the Japan Aerospace Exploration Agency and European Space Agency will launch missions that will bring back samples from Phobos.