The two explanets have periods of 19.2 days (Kepler-9b) and 38.9 days (Kepler-9c).
Kepler-9 is a star that is located in the constellation Lyra. It has a mass slightly larger than the Sun's mass - at 1.213 the mass of the Sun.
These periods of the exoplanets were found to be changing, though. The first period (19.24 days) is increasing at an average rate of 4 minutes per orbit, while the second period (38.91 days) is decreasing at an average rate of 39 minutes per orbit.
Dr. Matthew J. Holman, from the Harvard-Smithsonian Center for Astrophysics (Cambridge, Massachusetts) and one of the researchers on the discovery, states within the NASA article, "This discovery is the first clear detection of significant changes in the intervals from one planetary transit to the next, what we call transit timing variations.'
Holman adds, 'This is evidence of the gravitational interaction between the two planets as seen by the Kepler spacecraft."
The scientists also found that these two explanets are slightly less massive that the planet Saturn.
Oftentimes exoplanets are compared to the mass of Jupiter (the largest planet in our solar system), rather than Saturn (the second largest one). Saturn is 95 times the mass of Earth, while Jupiter is about 318 times the mass of Earth.
Kepler-9b is 0.252 times the mass of Jupiter, and Kepler-9c is 0.171 times Jupiter's mass.
Page three concludes with more information from the Science magazine and the NASA article.