It is also predicted that Phobos , a moon of Mars , will break up and form into a planetary ring in about 50 million years .
Phobos ' low orbit with an orbital period that is shorter than Mars Martian day is decaying due to tidal deceleration .
It is also predicted that Phobos , a moon of Mars , will break up and form into a planetary ring in about 50 million years , because its low orbit with an orbital period that is shorter than a Martian day is decaying due to tidal deceleration .