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 P , a P ) correlation consistent with a collision event near true anomaly of ∼ 180 • with ejecta velocity v ej ∼ 285 m/s. The ejecta distribution from a collision with these orbital properties is predicted to have a maximum semimajor axis dispersion of δa ej = 0.005 ± 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 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 lowalbedo families associated with (495) Eulalia. The second Eulalia family may be a high-a P , low-e P , low-i P component of the first Eulalia family-forming collision, possibly explained by an anisotropic ejection field.

The Flora family resides in the densely populated inner main belt, bounded in semimajor axis by the ν 6 secular resonance and the Jupiter 3:1 mean motion resonance. The presence of several large families that overlap dynamically with the Floras (e.g., the Vesta, Baptistina, and Nysa-Polana families), and the removal of a significant fraction of Floras via the nearby ν 6 resonance complicates the Flora family's distinction in both proper orbital elements and reflectance properties. Here we use orbital information from the Asteroids Dynamic Site (AstDyS), color information from the Sloan Digital Sky Survey (SDSS), and albedo information from the Wide-field Infrared Survey Explorer (WISE) to obtain the median orbital and reflectance properties of the Floras by sampling the core of the family in multidimensional phase space. We find the median Flora SDSS colors to be a * = 0.126 ± 0.007 and i − z = −0.037 ± 0.007; the median Flora albedo is p V = 0.291 ± 0.012.These properties allow us to define ranges for the Flora family in orbital and The size-dependent dispersion of the Flora members in semimajor axis (the "V" plot) then yields an age for the family of 910 +160−120 My, with the uncertainty dominated by the uncertainty in the material properties of the family members (e.g., density and surface thermal properties). We discuss the effects on our age estimate of two independent processes that both introduce obliquity variations among the family members on short (My) timescales: 1) the capture of Flora members in spin-orbit resonance, and 2) YORP-driven obliquity variation through YORP cycles. Accounting for these effects does not significantly change this age determination.

Potentially hazardous asteroids (PHAs) represent a unique opportunity for physical characterization during their close approaches to Earth. The proximity of these asteroids makes them accessible for sample-return and manned missions, but could also represent a risk for life on Earth in the event of collision. Therefore, a detailed mineralogical analysis is a key component in planning future exploration missions and developing appropriate mitigation strategies. In this study we present near-infrared spectra (∼ 0.7-2.55 µm) of PHA (214869) 2007 PA8 obtained with the NASA Infrared Telescope Facility during its close approach to Earth on November 2012. The mineralogical analysis of this asteroid revealed a surface composition consistent with H ordinary chondrites. In particular, we found that the olivine and pyroxene chemistries of 2007 PA8 are Fa 18 (Fo 82 ) and Fs 16 , respectively. The olivine-pyroxene abundance ratio was estimated to be 47%. This low olivine abundance and the measured band parameters, close to the H4 and H5 chondrites, suggest that the parent body of 2007 PA8 experienced thermal metamorphism before being catastrophically disrupted. Based on the compositional affinity, proximity to the J5:2 resonance, and estimated flux of resonant objects we determined that the Koronis family is the most likely source region for 2007 PA8.

No abstract