The shape of an orbit is a conic section with the center of mass at one focus. Curves found by cutting a cone with a plane. Mass. Because the Earth is so much smaller than the Sun, their mutual center of mass is inside the Sun, so the difference is not immediately apparent. These are curves formed by the intersection of a cone and a plane cutting it at various angles. Orbits are bound and objects orbit perpetually.
Orbits are unbound and objects escape .
Second Law of Orbital Motion Orbital motions conserve angular momentum. The proportionality between the square of the period and the cube of the semi-major axis now depends on the masses of the two bodies. In Kepler's version, the constant of proportionality works out to be 1.0 if we use units of years for P and AUs for the semi-major axis, a. While computationally convenient, it hides the underlying dependence on the mass of the Sun from sight. The problem with empirical laws, like Kepler's formulation, is that they only show the surface, not the important details underlying them.