Identifying Outer Solar System Materials in the Main Belt

Many small solar system bodies, including asteroids and trans-Neptunian objects, have red spectral slopes (that is, increasing reflectance with increasing wavelength) in the visible and near infrared (VNIR). Objects in the outer Solar System (e.g. TNOs, Centaurs) tend to have redder spectral slopes than those closer to the Sun (e.g. Jupiter Trojans, Main Belt asteroids). While this general trend has been interpreted as reflecting an initial gradient in temperature and thus a difference in available condensation materials (organics, ices) in the protosolar nebula (e.g. Brown et al. 2011, Hainaut & Delsanti, 2012) subsequent interactions between small bodies and the major planets have led to radial mixing, resulting in the implantation of reddish outer Solar System-like materials in the inner Solar System (e.g. DeMeo et al. 2014, Hasegawa et al. 2021). We present the preliminary results of our ongoing survey of candidate “red” objects in the Main Belt. We also present the VNIR spectra of several asteroids with highly red slopes. Using spectrophotometry from the Sloan Digital Sky Survey Moving Object Catalog (SDSS MOC), we identify potential “red” objects by selecting those with spectral slopes equal to or exceeding the average spectral slope of the reddest Trojan asteroids. Using the NASA IRTF and Lowell Discovery Telescope, we observed these candidate objects to determine their spectral slopes in the VNIR region to determine how many of these candidate objects truly have highly red slopes that indicate an outer solar system origin. Our confirmation rate of ~50% can be extrapolated from our sample to the rest of the SDSS MOC to estimate the amount of outer Solar System material delivered to the Main Belt. Estimating the amount of outer Solar System material that has been implanted in the Main Belt will provide additional constraints on models of early planetary migration.