Data from W. H. Ip et al. (2016) showing the past orbital evolution of 9P/Tempel 1 over the last 3000 yr. The shaded area marks the interval between 1200 and 600 yr ago, corresponding to the estimated formation period of the large smooth patch. Notably, this timeframe coincides with the most abrupt orbital changes, during which the perihelion decreased from ∼4 to 2.3 au before returning to ∼4 au.