Projected distance between β Pic b and its host star in milliarcsecond (mas) as a function of time. The colors of the symbols are the same as in Fig. 1. Upper panels: measured positions of the planet with their error bars, along with the best fit obtained with an orbital period of about 18.0 years. Bottom panels: residual differences between the measurements and the fit with the assumption that the planet transited in 1981. Right panels: zoom on the projected distances and residuals for the 2009–2015 time period.