The eccentricity (e) of an orbit describes its shape. An orbit with an eccentricity of:
- e = 0 is a perfect circle.
- 0 < e < 1 is an elliptical orbit.
- e = 1 is a parabolic trajectory.
- e > 1 is a hyperbolic trajectory.
Among the given options:
- e = 0.001 (almost circular)
- e = 0.90 (highly elliptical)
- e = 1 (parabolic)
- e = 0.25 (elliptical)
The least eccentric orbit, which is the most circular, is e = 0.001.