Behavior of perihelion distance (panel a), semi-major axis (panel b), eccentricity (panel c), and inclination to the ecliptic (panel d) of the initially nominal orbit of comet 2P/Encke, which is (violet curve) or is not (red curve) influenced by the non-gravitational force (jet effect). The evolution of the corresponding elements of the orbits of the second set of its clones (green curves), which delimit the uncertainty of non-gravitational parameters A₁ and A₂, are also shown. The evolution is reconstructed backward for 50 000 yr.