a scanning instrument, the time of the observation was computed from the image line determined from the centroid measurement. Figure 3 shows the orientation and scan direction of the three HiRISE images acquired on 2014 October 7. 

The measured astrometric positions are reported in the first block of Table 2. To account for the uncertainties resulting from centroiding, MRO ephemeris errors, and the small number of reference stars in the field of view, we conservatively weighted these data at 1 $^{′′}$. We chose these weights according to an assessment of the internal consistency of the data and the estimated systematic errors. 

Figure 4 shows the HiRISE astrometric positions with respect to solu- tions 95 and 97. These positions are clearly inconsistent with solution 97, which we had deemed as more likely. On the other hand, solution 95 pro- vide an excellent prediction for the HiRISE observations, thus confirming the (unexpectedly) large out-of-plane component of the nongravitational pertur- bations. 

The 2014 October 7 HiRISE observations removed the prejudice on A$_{3}$ by showing that the large out-of-plane perturbation seen in solution 95 was real and not an artifact of unresolved issues in the astrometry. Since solution 95 and 97 would have led to different field of views for the close approach ob- serving sequence, these HiRISE observations were decisive to obtain accurate ephemerides for the Mars encounter. 

