The Nysa-Polana complex is a group of low-inclination asteroid families in the inner main belt , bounded in semimajor axis by the Mars-crossing region and the Jupiter 3:1 mean-motion resonance .
This group is important as the most likely source region for the target of the OSIRIS-REx mission , ( 101955 ) Bennu ; however , family membership in the region is complicated by the presence of several dynamically overlapping families with a range of surface reflectance properties .

The large S-type structure in the region appears to be associated with the parent body ( 135 ) Hertha , and displays an ( e _ { \text { P } } ,a _ { \text { P } } ) correlation consistent with a collision event near true anomaly of \sim 180 ^ { \circ } with ejecta velocity v _ { \text { ej } } \sim 285 m/s .
The ejecta distribution from a collision with these orbital properties is predicted to have a maximum semimajor axis dispersion of \delta a _ { ej } = 0.005 \pm 0.008 AU , which constitutes only a small fraction ( 7 % ) of the observed semimajor axis dispersion , the rest of which is attributed to the Yarkovsky effect .
The age of the family is inferred from the Yarkovsky dispersion to be 300 ^ { +60 } _ { -50 } My .

Objects in a smaller cluster that overlaps the large Hertha family in proper orbital element space have reflectance properties more consistent with the X-type ( 135 ) Hertha than the surrounding S-type family .
These objects form a distinct Yarkovsky “ V ” signature in ( a _ { \text { P } } ,H ) space , consistent with a more recent collision , which appears to also be dynamically connected to ( 135 ) Hertha .
Production of two families with different reflectance properties from a single parent could result from the partial differentiation of the parent , shock darkening effects , or other causes .

The Nysa-Polana complex also contains a low-albedo family associated with ( 142 ) Polana ( called “ New Polana ” by ) , and two other low-albedo families associated with ( 495 ) Eulalia .
The second Eulalia family may be a high- a _ { \text { P } } , low- e _ { \text { P } } , low- i _ { \text { P } } component of the first Eulalia family-forming collision , possibly explained by an anisotropic ejection field .