Data of six flybys, those of Galileo I, Galileo II, NEAR, Cassini, Rosetta
and Messenger were reported by Anderson et al \citep{Anderson}. Four of them:
Galileo I, NEAR, Rosetta and Messenger gain Newtonian energy during the flyby
transfer, while Galileo II and Cassini lose energy. This is, in both cases, a
surprising anomaly since Newtonian forces derive from a potential and they are,
therefore, conservative. We show here that the gravitational field of a
rotating planet as derived from a new model introduces a non conservative force
that gives a partial, but in our opinion satisfactory, explanation of these
anomalies and suggests a correlation between the sign of the anomaly and the
sign of the azimuthal velocity at perigee.Comment: 12 pages, 3 figure