Martian moons: Phobos -- The team concluded that Phobos is likely to contain large voids, which makes it less likely to be a captured asteroid. Its composition and structural strength seem to be inconsistent with the capture scenario. It is possible that Phobos formed in situ at Mars, from ejecta from impacts on the Martian surface, or from the remnants of a previous moon which had formed from the Martian accretion disc and subsequently collided with a body from the asteroid belt. Data from the Mars Express OMEGA spectrometer suggests Phobos has a primitive composition, so primitive materials must have been available for accretion during its formation. The circular orbit suggests that Phobos formed in situ whilst analysis of the Planetary Fourier Spectrometer data from Mars Express also points towards in situ formation but does not rule out the possibility that Phobos is a captured achondrite-like meteor.
NO WAY would I dare name a big hole after my wife.