The plot shows two things:
Predicted development of Apophis’ position uncertainty over time (blue, red, black lines). Optical measurements made in 2011 are expected to cut uncertainties in half. Optical and radar measurements in 2013 should reduce uncertainties below 50 km. If Arecibo is able to determine a shape and pole, uncertainties could be reduced 94% relative to optical data only.
Minimum/maximum effects of dynamics not considered in the Standard Dynamical Model (gold lines). These dynamics could be visible in 2013, especially in Arecibo measurements, depending on their magnitude. Prior to then, the changes will be too small to be detected by even the best ground-based measurements.
Figure by J. Giorgini (JPL).