We constrain the true spin-orbit alignment of the KOI-89 system by numerically fitting the two Kepler photometric lightcurves produced by transiting planets KOI-89.01 and KOI-89.02 .
The two planets have periods of 84.69 days and 207.58 days , respectively .
We find that the two bodies are low-density giant planets with radii 0.45 \pm 0.03 \leavevmode \nobreak \mathrm { R _ { jup } } and 0.43 \pm 0.05 \leavevmode \nobreak \mathrm { R _ { jup } } and spin-orbit misalignments 72 ^ { \circ } \pm 3 ^ { \circ } and 73 ^ { \circ + 11 } _ { \leavevmode \nobreak -5 } , respectively .
Via dynamic stability tests we demonstrate the general trend of higher system stability with the two planets close to mutual alignment and estimate their coalignment angle to 20 ^ { \circ } \pm 20 ^ { \circ } – i.e .
the planets are misaligned with the star but may be aligned with each other .
From these results , we limit KOI-89 ’ s misalignment mechanisms to star-disk-binary interactions , disk warping via planet-disk interactions , planet-planet scattering , Kozai resonance , or internal gravity waves .