improved very fast. As early as 1965 the features of Venus were tracked with a maximum uncertainty of $3$ km [@Tausworthe] by Deep-Space radars. Subsequent missions to Jupiter has allowed also a high-accuracy determination of the orbits of the moons of this planet. Starting from Eq. (\[Ftid\]) we get an estimation of the perturbation of the tidal forces as a function of the uncertainty in the position $\delta {\bf R}$:

$$\begin{array}{rcl}
\delta \bm{\mathcal{F}}_{\mbox{tidal}}&=&\mu \left(-\displaystyle\frac{\delta {\bf R}}{R^3}+3 \displaystyle\frac{{\bf R}}{R^5}{\bf R} \cdot \delta {\bf R}\right.\\
\noalign{\smallskip}
&+&\displaystyle\frac{\delta {\bf R}}{\left(r^2+R^2-2 {\bf r}
\cdot {\bf R} \right)^{3/2}} \\
\noalign{\smallskip}
&-&\left. 3 \displaystyle\frac{\left({\bf R}-{\bf r}\right) \cdot \delta {\bf R}}{\left(r^2+R^2-2 {\bf r}
\cdot {\bf R} \right)^{5/2}} \left( {\bf R}-{\bf r}\right)   \right)\; .
\end{array}$$

Assuming an error of $3$ km in a random direction for the position of Io we get an uncertainty in the tidal acceleration exerted upon Juno of $10^{-13}$ km$/$s$^2$, which it is certainly very small and can be dismissed as the origin of the possible anomaly discussed in this paper.

Mismodelling of the zonal coefficients is also a source of error. For example, a variation of $J_2$ by $10^{-8}$ would imply, according to Eqs. (\[Fgeor\]) and (\[Fgeot\]), a perturbing force of magnitude $\vert 