Mars' Moon Phobos May Become a Planetary Ring Before Clumping Again to Form Another Moon

Scientists from Purdue University have developed a new theory suggesting that Mars' moon, Phobos, might actually collapse one day and form a planetary ring around the red planet.

Their theory, described in a paper published in the journal Nature Geosciences, showed that it's possible for the debris from asteroids or other objects that slammed into Mars around 4.3 billion years ago to alternate between becoming a planetary ring and clumping up to form a moon.

"That large impact would have blasted enough material off the surface of Mars to form a ring," said Andrew Hesselbrock, a doctoral student in physics and astronomy at Purdue University, in a press release.

Hesselbrock, together with Earth, atmospheric and planetary sciences Assistant Professor David Minton, developed a new model based on their theory.

The model suggests that a large impact between Mars and an asteroid could send debris into the space. The debris could form into a ring. And as the debris in the ring slowly move away from the red planet and spread out, they began to clump and eventually form a moon.

As time goes by, the newly formed moon will be pulled back by the planet's gravity until it reaches the Roche limit -- the distance within which the planet's tidal forces will break apart a celestial body that's held together only by gravity.

In their model, Mars' moon Phobos is estimated to break apart and become a planetary ring in roughly 70 million years. The researchers believe that Phobos had been alternating between becoming a planetary ring and becoming a moon about three to seven times over billions of years.

Every time a moon is ripped apart in the Roche limit, some of its debris would have rained down in the red planet, possibly explaining enigmatic sedimentary deposits found near Mars' equator. As the cycle of being ripped apart and clumped together go on, the researchers predict that the successor moon would be five times smaller than the last.