Extent of the potential well of the effective potential U(r) for particles emitted at different points along the orbit of the comet Ikeya–Seki, parametrized by the angle χ counted from the perihelium. The upper (lower) half of the dotted oval shows the value of (). The dashed line shows the heliocentric distance r₀ to the point at which the particle was emitted. We note that the oval does not extend to more distant parts of the orbit, where the extremum points of U(r) are absent.