The Spectral Slopes of the Polana-Eulalia Complex: Observations of Small Members and Heterogeneity

The Polana-Eulalia Complex (PEC) is a low-albedo, inner Main Belt (MB) family of C-complex asteroids that is critical for understanding the dynamical evolution of the solar system. The ν₆ secular resonance – the inward bound for the PEC – serves to funnel MB asteroids into the inner solar system in a manner that preferentially ejects the smallest members. This dynamical pathway to the inner solar system is the presumed scenario for the emplacement of both Bennu and Ryugu, which are Near-Earth Asteroids of C-complex classification and targets of ongoing spacecraft missions. The PEC – while composed of the Polana Family and the Eulalia Family – exhibits spectral homogeneity in both visible and Near-IR (0.8 – 4.0 μm) wavelengths (de Leon et al., 2016; Pinalla-Alonso et al., 2016). However, Bennu displays a blue Near-IR spectral slope, while all currently observed PEC members and Ryugu exhibit red Near-IR spectral slopes (Pinalla-Alonso et al., 2016 and references therein). Thus, Bennu’s Near-IR slope discrepancy with its presumed origin in the MB presents an ongoing problem in understanding Bennu’s evolution. A potential resolution may be deduced through investigating the relationship between PEC member size and spectral slope. Thomas et al. (2021) provided evidence that space weathering induces complex, size-dependent spectral slope trends amongst MB C-complex families. While the PEC was not included in their work, the presumed family of origin for Bennu and Ryugu should exhibit a spectral slope dependency with size. Thus, this work seeks to investigate the spectral slope trends of both the smallest (sub-km) PEC members as well as all PEC members observed in the 4^th release of the Sloan Digital Sky Survey Moving Object Catalog (SDSSMOC4). We present fluxes from the g’, r’, i’, and z’ filters for a preliminary suite of confirmed, sub-km PEC members. We also present the relationship between spectral slope and size for the Polana Family, the Eulalia Family, and the combined PEC by using the members found in the SDSSMOC4. In total, we provide evidence for a size-based spectral slope trend for the PEC (and its constituent families), and we demonstrate that the Polana and Eulalia Families exhibit spectral slope heterogeneity, which is in contrast with the previous literature.