Today I learned that Triton has an orbital eccentricity is very low 0.000016 -->> almost perfectly circular
I wondered why the eccentricity was so low, so I googled it and found that we don’t really know why it is so low. (Triton also seems to be the only large moon with a retrograde orbit. I think that it is also the only moon with an inclination larger than 10 degrees. (The inclination of Triton’s orbit is 130 degrees ( 129.812° (to the ecliptic))).) https://astronomy.stackexchange.com/questions/19639/why-is-the-eccentricity-of-triton-so-low Moon Name Eccentricity of Orbit Charon 0.0002 Triton 0.000016 (Retrograde, Large Inclination) Titania 0.0011 Oberon 0.0014 Titan 0.0288 IO 0.0041 Ganymede 0.0013 Deimos 0.00033 Phobos 0.0151 The Moon 0.059