Its planetary system, discovered by the Kepler Mission in 2010 was the first detected with the transit method found to contain multiple planets.

Kepler-9 was named for the Kepler Mission, a project headed by NASA that was designed to search for Earth-like planets.

[8] In June 2010, some 43 days after Kepler came online, its operating scientists submitted a list of over 700 exoplanet candidates for review.

Kepler-9 was one of the multiplanetary systems; it was identified as such when scientists noticed significant variations in the time intervals at which Kepler-9 was transited.

These orbital changes allowed the masses of the planets (a parameter not normally obtainable via the transit method) to be estimated using a dynamical model.

The mass estimates were further refined using radial velocity measurements obtained with the HIRES instrument of the Keck 1 telescope.