For Mars’s moon Phobos, it’s dust to dust. There is evidence that the misshapen little moon has gone through a cycle of being smashed up and spreading into a ring around Mars before coalescing into a solid moon again.
This ring-moon cycle was proposed in 2017, and new simulations by Matija Ćuk at the SETI Institute in California, and his colleagues show that such a cycle for Phobos may have forced Mars’s other moon, Deimos, …
source: newscientist.com