We validate the planetary origin of the KOI-1599 transit time variations ( TTVs ) with statistical and dynamical tests .
We re-analysed KEPLER Q1-Q17 light-curves of the star , and we independently derived the TTVs .
They appear as strongly anti-correlated , suggestive of two mutually interacting planets .
We found similar radii of the candidates , 1.9 \pm 0.2 \mbox { R } _ { \oplus } for the inner KOI-1599.02 , and 1.9 \pm 0.3 \mbox { R } _ { \oplus } for the outer KOI-1599.01 .
The standard MCMC TTV analysis constrains the planet masses safely below the dynamical instability limit of \simeq 3 \mbox { M } _ { { \mbox { \scriptsize Jup } } } .
The best-fitting MCMC model yields ( 9.0 \pm 0.3 ) \mbox { M } _ { \oplus } , and ( 4.6 \pm 0.3 ) \mbox { M } _ { \oplus } , for the inner and the outer planet , respectively .
The planets are trapped in 3:2 mean motion resonance ( MMR ) with anti-aligned apsides ( \Delta \varpi = 180 ^ { \circ } ) at low-eccentric ( e \simeq 0.01 ) orbits .
However , we found that the TTV mass determination depends on eccentricity priors with the dispersion in the ( 0.01,0.05 ) range .
They permit a second family of TTV models with smaller masses of \simeq 7 \mbox { M } _ { \oplus } , and \simeq 3.6 \mbox { M } _ { \oplus } , respectively , exhibiting two modes of \Delta \varpi = 0 ^ { \circ } , 180 ^ { \circ } librations .
The 3:2 MMR is dynamically robust and persists for both modes .
In order to resolve the mass duality , we re-analysed the TTV data with a quasi-analytic model of resonant TTV signals .
This model favours the smaller masses .
We also reproduced this model with simulating the migration capture of the system into the 3:2 MMR .