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Abstract

The findings of Micheli et al. (Nature2018,559, 223–226) that 1I/2017 U1 (‘Oumuamua)showed anomalous orbital accelerations have motivated us to apply an impact model of gravityin search for an explanation. A small deviation from the1/rpotential, whereris the heliocentricdistance, is expected for the gravitational interaction of extended bodies as a consequence of thismodel. This modification of the potential results from an offset of the effective gravitational centrefrom the geometric centre of a spherically symmetric body. Applied to anomalous Earth flybys,the modelaccounts for energy gains relative to an exact Kepler orbit and an increased speed of severalspacecraft. In addition, the flat rotation profiles of eight disk galaxies could be explained,as well asthe anomalous perihelion advances of the inner planets and the asteroid Icarus. The solution in thecase of ‘Oumuamua is also based on the proposal that the offset leads to an approach and flybytrajectory different from a Kepler orbit without postulating cometary activity. As a consequence,an adjustmentof the potential and centrifugal orbital energies can be envisaged outside the narrowuncertainty ranges of the published post-perihelion data without a need to re-analyse the original data.The observed anomalous acceleration has been modelled with respect to the orbit solutions JPL 16and “Pseudo-MPEC” for 1I/‘Oumuamua.