If this is confirmed, it will have a bearing on models that suggest the Moon was formed from material thrown off from the Earth. The locations of other similar rocks suggest that they were excavated and thrown across the Moon by the impact. During the early days of lunar exploration it became clear that the gravitational field round the Moon was not uniform. This posed great problems to mission designers, since corrections had to be made to the orbit of the lunar spacecraft, yet there were tight constraints on the amount of fuel they could carry. A complete gravity map of the Moon was not produced until data were returned from Clementine, but this has now been surpassed by Lunar Prospector, which has provided the most detailed gravity maps yet.
Gravity anomalies occur over regions of either very high or very low density.
Mapping these can therefore give indications of the surface and interior structure of the Moon. The highest anomalies occur over the nearside maria, which contain dense basaltic material. Lunar Prospector has discovered three new anomalies and found suggestions of four more that may be confirmed during the analysis of data from the extended mission. Perhaps more importantly the gravity experiment, together with measurements using the magnetometer, has provided estimates of the size of the lunar core, something that has remained elusive until now. This is an important result, as it helps to constrain models of how the Moon formed.