Jack Wisdom discovered sudden jumps in this quantity in test asteroids placed near the 3/1 commensurability of a restricted three-body problem. In hierarchical triple systems, mutual inclination and this quantity for the inner binary oscillate due to angular momentum exchange between the binaries. (10[1])This quantity equals the square root of the expression: “one, plus 2 times energy times angular momentum squared, over reduced mass times k squared,” where k is the constant in the force law. This quantity is the magnitude of a vector that always points towards the periapsis. The denominator of the orbit equation contains the term: “this quantity times the cosine of true anomaly.” When this quantity is less than 1, energy is negative, so the orbit is bound. This quantity and the semi-major axis describe the size and shape of an orbit. For 10 points, name this quantity that is between zero and one for an elliptical orbit. ■END■