Robert Clark pointed out:

This NASA page on Mars does give the eccentricity as about 0.1 :



Mars Fact Sheet
http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html

However, note that it gives the perihelion distance as 206.62 million km and the aphelion distance as 249.23. This is an increase in distance of 20%, which results in a change in illumination of
above 40%.
By eccentricity they must be using the mathematical definition of eccentricity as applied to an ellipse which is the distance between the foci divided by the major axis. Doing the algebra you see if the eccentricity using this definition is e, then the ratio of the aphelion distance to perihelion distance is (1+e)/(1-e) , which does give a ratio of about 1.2 for Mars' orbit.



I think I fail geometry 101.