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))).)



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

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