Astrometric observations of Deimos

For this study, we have developed a new technique, where the center-of-figure of the odd-shaped Deimos was determined by fitting the predicted to the observed satellite limb. The prediction of the limb was made based on the moon's known shape model.

The camera pointing was verified and corrected by means of background star observations. We obtained a set of spacecraft- centered Deimos coordinates with accuracies between 0.6 and 3.6km (1 sigma). Comparisons with current orbit models indicate that Deimos is ahead or falling behind its predicted position along its track by as much as +3.7km or -4.4km, respectively, depending on the chosen model.