The 'eccentricities' ( defined as 1 - minor axis/major axis) of the planetary orbits are as follows:
Mercury 0.205 Venus 0.007 Earth 0.017 Mars 0.093 Jupiter 0.048 Saturn 0.055 Uranus 0.047 Neptune 0.008 Pluto 0.250A perfect circle is 0.000 on this scale. For Earth, if you were to draw a circle 10 centimeters in radius, the true orbit of the Earth would be an ellipse that is 1.7 millimeters shorter in radius along the 'minor axis'. But, as we see for Pluto, and for many of the newly discovered planets around nearby stars, the nearly-circular orbits of our planets are rather unusual. The new planet around 61 Cygni B has a very large eccentricity, similar to Pluto's, and it is 1.5 times the mass of Jupiter to boot!