There have been discussions about the oddities of the Mars moons for years now, this suggests that we may have finally got to grips with the data - as you can see, I have a small moon orbiting my icon...
Like the gas giants in the outer region of the Solar System, Mars may have been circled by a ring of debris over three billion years ago. Astronomers from the SETI Institute and Purdue University have spotted tantalizing signs that the red, rocky planet once supported a ring system. The clues lie in its two potato-shaped moons …
...have used the odd orbit and size of Mars' moons, especially Deimos, as story lines or plot points because "hey! That's no moon, it's an alien spaceship/space station/monitoring device/stargate/early warning system" (and people thought that was a new trope invented for the johnny-come-lately Star Wars film.)
There is still water on Mars. Seems like most of it is trapped in the south polar ice cap, but more has been discovered under the surface in the Utopia Planitia region (wherever that is).
That said, when Mars lost most of its atmosphere and it dropped to the 1% density it has today, all surface water that wasn't frozen simply boiled off and was swept away by the Sun's wind. I have trouble finding a reference as to when that happened exactly.
I think in the general case, the spinning of the planet causes it to become an ellipsoid (it bulges at the equator and shrinks in pole-to-pole distance). This causes an asymmetrical gravitation field; debris are not pulled towards the exact center of gravity of the planet, but towards the equator because that bulge is closer. Thus all particles are gradually pulled into the equatorial plane, where they form a very thin disk.
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