This provides an extremely sensitive method capable of detecting additional planets in the system with masses potentially as small as that of Earth.Detecting this effect by measuring the change is known as transit-timing variations.The first significant detection of a non-transiting planet using transit-timing variations was carried out with NASA's Kepler telescope.[12] Transit-timing variation was first convincingly detected for planets Kepler-9b and Kepler-9c [13] and gained popularity by 2012 for confirming exoplanet discoveries.By performing a series of analytical (TTVFaster[15]) and numerical (TTVFast[16] and Mercury[17]) n-body integrations of a system of six gravitationally interacting, co-planar planets, the initial mass estimates for the six inner planets of TRAPPIST-1, along with their orbital eccentricities, were determined.
Animation showing difference between planet transit timing of 1-planet and 2-planet systems. Credit: NASA/Kepler Mission.