The first exoplanets were all found using the radial velocity method of measuring the “wobble” of a star — movement caused by the gravitational pull of an orbiting planet.
Radial velocity has been great for detecting large exoplanets relatively close to our solar system, for assessing their mass and for finding out how long it takes for the planet to orbit its host star.
But so far the technique has not been able to identify and confirm many Earth-sized planets, a primary goal of much planet hunting. The wobble caused by the presence of a planet that size has been too faint to be detected by current radial velocity instruments and techniques.
However, a new generation of instruments is coming on line with the goal of bringing the radial velocity technique into the small planet search. To do that, the new instruments, together with their telescopes. must be able to detect a sun wobble of 10 to 20 centimeters per second. That’s quite an improvement on the current detection limit of about one meter per second.