Kepler has discovered hundreds of systems with multiple transiting exoplanets which hold tremendous potential both individually and collectively for understanding the formation and evolution of planetary systems .
Many of these systems consist of multiple small planets with periods less than \sim 50 days known as Systems with Tightly-spaced Inner Planets , or STIPs .
One especially intriguing STIP , Kepler-80 ( KOI-500 ) , contains five transiting planets : f , d , e , b , and c with periods of 1.0 , 3.1 , 4.6 , 7.1 , 9.5 days , respectively .
We provide measurements of transit times and a transit timing variation ( TTV ) dynamical analysis .
We find that TTVs can not reliably detect eccentricities for this system , though mass estimates are not affected .
Restricting the eccentricity to a reasonable range , we infer masses for the outer four planets ( d , e , b , and c ) to be 6.75 ^ { +0.69 } _ { -0.51 } , 4.13 ^ { +0.81 } _ { -0.95 } , 6.93 ^ { +1.05 } _ { -0.70 } , and 6.74 ^ { +1.23 } _ { -0.86 } Earth masses , respectively .
The similar masses but different radii are consistent with terrestrial compositions for d and e and \sim 2 % H/He envelopes for b and c. We confirm that the outer four planets are in a rare dynamical configuration with four interconnected three-body resonances that are librating with few degree amplitudes .
We present a formation model that can reproduce the observed configuration by starting with a multi-resonant chain and introducing dissipation .
Overall , the information-rich Kepler-80 planets provide an important perspective into exoplanetary systems .