Whatever a moons origin, its orbit will continue to evolve as a result of the gravitational interaction with its primary (in how cases - Earth), as each body tries to maintain its own orbital momentum against the others gravitational pull. One stage of this process, known as tidal locking or synchronous spin, is common in our solar system and evident in the relationship between Earth and its moon. In such a system, the planets tidal pull slows the moons rotation until it spins once on its axis in the period it takes to complete one orbit. There after, the planet locks onto the long axis of the distorted moon, causing it always to keep the same side facing towards the planet. As this evolution continues, the moon and planet can achieve the condition called mutual synchronous spin, whereby the moon will complete one revolution around the planet in the same time it takes the planet to rotate once on its axis.

  As a result not only will the moon keep one face towards the planet, but the planet will show only one face to the moon. The moon thus will be visible from only one side of the planet and, neither rising nor setting, will hang monitionless in the sky.

Whether a moon and planet ultimately reach this stable situation depends on the moon's being able to slow the planets rate of rotation. Two fates are possible, according to whether the moon is outside the boundary called the synchronous orbit distance. This distance is unique for each planet and is determined by the rate at which the planet spins on its axis. How ever, because this rate may be slowed over time by the tidal pull of the moon (as well as by gravitational interaction with the sun), the synchronous orbit distance is subject to change.

  A moon that lies within the synchronous orbit distance may be pulled in so close to the planet that is risks destruction, a process that could bring phobos-now circling Mars at a distance of only 6,050 km, crashing in to the Martian landscape in 70 million years or so (which could contain significance in this hypothesis regarding timeline). A moon that is just outside the critical distance may be boosted in to an ever higher orbits, much as Earth's moon, the Martian moon Deimos, and most larger of the satellite's in the solar system are being pushed outward from their primaries. Many eons hence, such a moons orbital altitude would coincide with the synchronous orbit distance and it would have achieved ultimate stability.  (source: Voyage Through The Universe - pages 62 & 63)

  So in our solar system, is this Earth Moon 'mutual synchronous spin' lock unique ? The answer is no ! Both the Earth and Moon share the same motion relationship as Charon does in the skies above Pluto.

  Is there further significance to be taken from this comparison ? Well yes. Until on recently Pluto was assumed to have had only one moon, however recent observations have brought to light, literally, the existence of two further moons.

  Could this therein carry some additional (significant) weight for our Earth itself having had a second, or perhaps third moon ?

Quote; "Two additional moons were imaged by astronomers working with the Hubble Space Telescope on May 15, 2005and received provisional designations of S/2005 P 1 and S/2005 P 2. They were confirmed with a series of "precovery" Hubble images from June 2002 through May 2003, which led to their orbits being determined. Additional follow-up observations were made in February and March 2006, confirming the orbit solutions.

  The small moons orbit Pluto at approximately two and three times the distance of Charon: P2 at 48,700 km and P1 at 64,800 km from the barycenter of the system. They have nearly circular prograde orbits in the same orbital plane as Charon, and are very close to but not in 4:1 and 6:1 mean motion orbital resonances with Charon.

  P1 is sometimes brighter than P2 and thus may be larger in some dimensions; alternately different parts of its surface may vary in brightness. Their sizes are not known but can be estimated from likely albedos. The moons' spectral similarity with Charon suggests a similar 35% albedo to Charon; this results in estimates of 46 km for P2 and 61 km for the brighter orientation of P1. Likely upper limits on their diameters can be estimated by assuming the 4% albedo of the darkest Kuiper Belt objects; these bounds are 137 ± 11km and 167 ±10km respectively. At the larger end of this range, the inferred masses are less than 0.3% of Charon's mass, or 0.03% of Pluto's." (source)

One of the most interesting things about Pluto is its orbit. Pluto takes 247.8 years to orbit the Sun, and the route that it takes is quite different from the other planets. The orbit is elliptical, and is inclined at an angle of 17 degrees relative to the orbits of the other planets. This special orbit means Pluto's furthest point from the Sun, or aphelion, is 7.4 billion kilometers, and its closest point, or perihelion, is 4.4 billion kilometers. Actually, from 1979 to 1999, Pluto's orbit was inside that of Neptune as can be seen on the lower diagram.

  Pluto perhaps another holds supportive key to the theory that the Earth had been struck by a Mars sized object. As mentioned, Pluto's orbit is elliptical, so perhaps the Mars size body that struck the Earth also had a likewise orbit. The impactor would have orbited either close to Venus (outside aphelion) or the opposite, a closer approach to Mars. Although we can only theorize the impactors actual density, the object would have had either a larger iron content or lower depending on its original accretion orbit. Most people usually assume that a Mars size object would have accreted between the Earth and Mars - though this thought likely comes from their mental connection when association is made to Mars in size.

  Although I've not had sufficient time available to seriosly crunch the numbers from all online material, I have attempted to plot the likely density of the object that collided with the Earth (fig. 5).

  This same diagram also reveals a few interesting ranges of densities of some of our solar systems bodies. As can been seen, the Earth, Venus and Mercury are all by far the most dense objects - and the strange similarity between Jupiter's two moons Europa and Io and how they fit comfortably either side of the moons density.

Comparison of terrestrial planets and larger moons according to density. Impact Object based on my research. (fig. 5)