How does the tilt and orbit of a planet affect its analemma shape?

[Swankie]

How come the analemma for Earth is in a "figure 8" form and Mars is circular? Does it have to do with radial velocity?

 

[Drakkith]

From wikipedia: http://en.wikipedia.org/wiki/Analemma

On Earth, the analemma appears as a figure eight, but on other solar system bodies it may be very different[3] because of the interplay between the tilt of each body's axis and the elliptical shape of its orbit.