Probability density distribution of the (458271) 2010 UM26 and 2010 RN221 convergence epoch. The calendar year is given at the abscissa, and the normalization of the ordinate assumes units in days. About 8% of the solutions are concentrated in a narrow peak centered at about 2003.5. These are simple head-on encounters. Longer-lasting encounters, shown in the left panel of Fig. 1, and the quasi-satellite solutions, shown in the right panel of Fig. 1, contribute to the tail that extends beyond the peak to the 1960s.