Exoplanet orbits
Figure 2. (a) A selection of the orbits inferred for several extrasolar planets (drawn to scale) together with the Earth's orbit (blue circle). The "hot Jupiters" have near-circular orbits and are buried at the centre of the diagram. Exoplanets with orbits more than few tenths of an astronomical unit are in highly elliptical orbits. (b) The departure from a circular orbit is quantified by its eccentricity, e. In an eccentric orbit, the star is located at one focus of the elliptical path traced out by the planet. The starplanet distance is a(1 e) at closest approach and a(1 + e) at maximum separation, where a is the semi-major axis and e is the eccentricity. Circular orbits have zero eccentricity.