We report the detection of three transiting planets around a Sunlike star , which we designate Kepler-18 .
The transit signals were detected in photometric data from the Kepler satellite , and were confirmed to arise from planets using a combination of large transit-timing variations , radial-velocity variations , Warm-Spitzer observations , and statistical analysis of false-positive probabilities .
The Kepler-18 star has a mass of 0.97 M _ { \sun } , radius 1.1 R _ { \sun } , effective temperature 5345 K , and iron abundance [ Fe/H ] = +0.19 .
The planets have orbital periods of approximately 3.5 , 7.6 and 14.9 days .
The innermost planet “ b ” is a “ super-Earth ” with mass 6.9 \pm 3.4 M _ { \oplus } , radius 2.00 \pm 0.10 R _ { \oplus } , and mean density 4.9 \pm 2.4 g cm ^ { − 3 } .
The two outer planets “ c ” and “ d ” are both low-density Neptune-mass planets .
Kepler-18c has a mass of 17.3 \pm 1.9 M _ { \oplus } , radius 5.49 \pm 0.26 R _ { \oplus } , and mean density 0.59 \pm 0.07 g cm ^ { − 3 } , while Kepler-18d has a mass of 16.4 \pm 1.4 M _ { \oplus } , radius 6.98 \pm 0.33 R _ { \oplus } , and mean density 0.27 \pm 0.03 g cm ^ { − 3 } .
Kepler-18c and Kepler-18d have orbital periods near a 2:1 mean-motion resonance , leading to large and readily detected transit timing variations .