Caption: Color image of the larger Martian moon the moon Phobos, taken by the Mars Reconnaissance Orbiter, 2008 Apr09.
Phobos' mean radius 11.1 km.
Crater Stickney is the largest crater on Phobos: it's quite obvious.
The commonest origin theory is that the Martian moons are captured asteroids, but rival theories exist (see Wikipedia: Moons of Mars: Origin).
The tidal force of Mars on Phobos is causing it to inspiral and it will break up and impact in fragments on Mars probably in 30--50 Myr (see Wikipedia: Phobos: Predicted destruction).
Credit/Permission: NASA,
2008 /
Public domain.
Image link: Wikipedia:
File:Phobos colour 2008.jpg.
Local file: local link: martian_moons_phobos.html.
File: Mars moons file:
martian_moons_phobos.html.