The dark surface of (163693) Atira and implications for inner-Earth asteroid origins
Abstract
We compare the physical properties of inner-Earth asteroid (163693) Atira with the NEOMOD3 population model. Its radar-derived diameter of 4.9 km and absolute magnitude HV≃16.4 imply a geometric albedo of pV∼0.02. Photometry with the Astrophysical Research Consortium 3.5-m telescope and ARCTIC yields g-r=0.49±0.03, r-i=0.20±0.02, i-z=0.02±0.03, a∗=−0.05±0.03, and a g-to-i spectral slope of 3.4±0.9%/100 nm. The photometric reflectance favors a provisional X-type classification; combined with the low albedo, it supports a Tholen P-type interpretation. NEOMOD3 assigns an approximately 66% probability of delivery through inner Main Belt channels and 26% to central and outer Main Belt channels. Atira's NEOMOD3 albedo-category probabilities are 0.07±0.02, 0.64±0.04, and 0.29±0.04 for pV<0.1, 0.1≤pV<0.3, and pV≥0.3, respectively. Across 38 inner-Earth objects, including Atira and 'Ayló'chaxnim, inner Main Belt delivery generally dominates, and intermediate albedo is favored for 33 objects. Atira therefore represents an uncommon low-albedo outcome, compatible with delivery of dark material from the inner Main Belt or more distant primitive populations. Further characterization of inner-Earth asteroids will test whether current population models reproduce their compositional diversity.
Related
- Nordic-based observations of binary asteroid (163693) Atira reveal a hydrated CM chondrite composition
- Surface regolith model of near-Earth asteroid (3200) Phaethon
- Visible, near‐, and thermal infrared spectra of asteroid Bennu samples: Relationship to and implications for remote sensing of carbonaceous asteroids
- Dynamical Behavior and Surface Features of Large Super-Fast Rotator Near-Earth Asteroid (436724) 2011 UW158
- Hydrogen Isotopic Fractionation in the Solar Nebula and Implications for Water in Earth and Inner Solar System Bodies.
BibTeX
@misc{bolin2026dark,
title = {{The dark surface of (163693) Atira and implications for inner-Earth asteroid origins}},
author = {Bryce T. Bolin and Carl Ingebretsen and Robert Jedicke and William F. Bottke and Colin Orion Chandler and Rogerio Deienno and Alessandro Morbidelli and David Nesvorný and Leo Y. Alcorn and Percy Gomez and Meredith A. MacGregor},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.40114},
eprint = {2610.40114},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.40114},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The dark surface of (163693) Atira and implications for inner-Earth asteroid origins
AU - Bryce T. Bolin
AU - Carl Ingebretsen
AU - Robert Jedicke
AU - William F. Bottke
AU - Colin Orion Chandler
AU - Rogerio Deienno
AU - Alessandro Morbidelli
AU - David Nesvorný
AU - Leo Y. Alcorn
AU - Percy Gomez
AU - Meredith A. MacGregor
PY - 2026
DA - 2026/10/29
PB - arXiv
DO - 10.48550/arxiv.2610.40114
UR - https://arxiv.org/abs/2610.40114
AB - We compare the physical properties of inner-Earth asteroid (163693) Atira with the NEOMOD3 population model. Its radar-derived diameter of 4.9 km and absolute magnitude H_V≃16.4 imply a geometric albedo of p_V∼0.02. Photometry with the Astrophysical Research Consortium 3.5-m telescope and ARCTIC yields g-r=0.49±0.03, r-i=0.20±0.02, i-z=0.02±0.03, a^∗=−0.05±0.03, and a g-to-i spectral slope of 3.4±0.9%/100 nm. The photometric reflectance favors a provisional X-type classification; combined with the low albedo, it supports a Tholen P-type interpretation. NEOMOD3 assigns an approximately 66% probability of delivery through inner Main Belt channels and 26% to central and outer Main Belt channels. Atira's NEOMOD3 albedo-category probabilities are 0.07±0.02, 0.64±0.04, and 0.29±0.04 for p_V<0.1, 0.1≤p_V<0.3, and p_V≥0.3, respectively. Across 38 inner-Earth objects, including Atira and 'Ayló'chaxnim, inner Main Belt delivery generally dominates, and intermediate albedo is favored for 33 objects. Atira therefore represents an uncommon low-albedo outcome, compatible with delivery of dark material from the inner Main Belt or more distant primitive populations. Further characterization of inner-Earth asteroids will test whether current population models reproduce their compositional diversity.
ER -