Many known exoplanets orbit close to their host star,within one-tenth of an astronomical unit (one AU is the average distance of the Earth from the Sun). Since their orbital periods are therefore very short and their gravitational influences on the host star's wobble comparatively large, they can be readily detected by the transit and velocity methods. What astronomers conclude not yet know is whether these planets formed near their present positions from natal circumstellar material close to their star, or whether instead they formed at distances larger than an AU and subsequently migrated inwards.
Source: phys.org