Spectral diversity of the inner belt primitive asteroid background population

1Anicia Arredondo,1Humberto Campins,2Noemi Pinilla-Alonso,3,4Juliade León,3Vania Lorenzie,5,6David Morat,3,4Juan Luis Rizos,2Mário De Prá
Icarus (in Press) Link to Journal [https://doi.org/10.1016/j.icarus.2021.114619]
1Physics Department, University of Central Florida, P.O. Box 162385, Orlando, FL 32816, USA
2Florida Space Institute, University of Central Florida, Orlando, FL 32816, USA
3Instituto de Astrofísica de Canarias, Tenerife, Spain
4Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
5Fundación Galileo Galilei – INAF, La Palma, Tenerife, Spain
6Observatório Nacional, Coordenação de Astronomia e Astrofísica, 20921-400 Rio de Janeiro, Brazil
Copyright Elsevier

We present new near-infrared spectra of 55 objects observed using the NASA InfraRed Telescope Facility and the Telescopio Nazionale Galileo, along with visible spectra of 21 objects obtained from the SMASS and S3OS2 surveys, to explore the differences in spectral slope and curvature between the background and the families and to show that the background is a possible source for both Bennu and Ryugu. Within the background population there is spectral diversity in taxonomy, spectral slope, and absorption band parameters. Our sample of asteroids shows that the background looks spectrally similar to the families in the same region, i.e., the background and families may have originated from the same or similar composition parent bodies. Average band center (0.69 ± 0.02 μm, depth: 2.3 ± 0.9%) of an ~0.7 μm absorption feature attributed to aqueous alteration is present in 30% of our primitive background asteroid sample, similar to abundances observed in other primitive inner belt asteroid families. Both near-Earth asteroid sample return mission targets, (101955) Bennu and (162173) Ryugu, are thought to have originated from primitive asteroid populations in the inner main belt, specifically from the low inclination asteroid families. A population that has not been explored spectrally but is dynamically able to deliver asteroid fragments to near-Earth space is the background population, i.e., asteroids that do not cluster into families. Based on our spectral comparisons, the primordial background is a possible source for (162173) Ryugu, but not for (101955) Bennu.

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