The uncertainty of science: The first results from the two GRAIL space probes have revealed that the Moon has a much thinner crust than previously believed.
These preliminary results have also found that the Moon’s surface topography closely matched the variations in the gravitational field, and that there appears no evidence in the gravitational field of the giant ancient impact basins that scientists have for decades assumed were there, based on surface evidence. This last result is especially surprising, and will force an almost complete rewrite of the Moon’s geological history.
Interestingly, these results are only peripherally related to GRAIL’s main research goal, which was to map the Moon’s deep structure and core. I suspect there are even more surprises coming when this data gets released.