Long-baseline ATLAS photometry of the seven main-belt asteroid targets of the Emirates Mission to the Asteroid Belt
Abstract
The Emirates Mission to the Asteroid Belt (EMA) will use the MBR Explorer spacecraft to fly past six main-belt asteroids -- (10253) Westerwald, (623) Chimaera, (13294) Rockox, (88055) Ghaf, (23871) Ousha and (59980) Moza -- before rendezvousing with, and deploying a lander onto, the extremely red (269) Justitia. We present a homogeneous analysis of a decade of sparse photometry of all seven targets from the Asteroid Terrestrial-impact Last Alert System (ATLAS). For each object we derive absolute magnitudes and phase slopes in the ATLAS c and o bands, the c-o colour on a common phase slope, a rotation period from a Lomb-Scargle periodogram of the phase-corrected light curve, and a light-curve amplitude setting a lower limit on elongation. Five periods are secure -- 3.243 h for Rockox, 33.1 h for Justitia, 3.64 h for Westerwald, 14.6 h for Chimaera and 4.36 h for Moza -- and agree with independent work; for Ousha aliasing leads us to adopt the published 8.35 h, while Ghaf remains unresolved. Lightcurve inversion gives a unique convex shape and spin state for Rockox and two pole solutions for Chimaera, Moza and Justitia; no model was obtained for Ghaf, Ousha or Westerwald, though Westerwald's spin axis must be retrograde. Combining the c-o colour with an albedo class from the phase slope, we classify the sample as one dark C-type (Chimaera), three probable S-types (Westerwald, Ghaf, Moza), two X-complex objects (Rockox, plausibly M-type, and Ousha, possibly E-type), and the exceptionally red L/D-type Justitia, whose (c-o) = 0.48 is redder than typical Jupiter Trojans. This only partly matches the mission's family-based expectation of a predominantly primitive target set, so we present these as testable predictions. Those of Ghaf and Ousha are least secure -- both disagree with published work and have unresolved or aliased periods -- and warrant follow-up.
Related
- Size, Albedo, and Taxonomy of Asteroid (1201) Strenua from Stellar Occultation and ATLAS Photometry
- Combination of multi-observatory photometry to determine asteroid rotation periods
- Aging in space: Space weathering age of S-type and V-type asteroid families from the Sloan Digital Sky Survey
- Discovery of activity on Main Belt Asteroid 6993 (1995 BJ4)
- Galactic cold clouds constraints on sub-GeV DM and asteroid-mass PBHs
BibTeX
@misc{erasmus2026longbaseline,
title = {{Long-baseline ATLAS photometry of the seven main-belt asteroid targets of the Emirates Mission to the Asteroid Belt}},
author = {Nicolas Erasmus and Josef Ďurech and David E. Trilling and Larry Denneau and John L. Tonry and Henry Weiland and Ken W. Smith and Javier Licandro and Miguel R. Alarcon},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.07404},
eprint = {2609.07404},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.07404},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Long-baseline ATLAS photometry of the seven main-belt asteroid targets of the Emirates Mission to the Asteroid Belt
AU - Nicolas Erasmus
AU - Josef Ďurech
AU - David E. Trilling
AU - Larry Denneau
AU - John L. Tonry
AU - Henry Weiland
AU - Ken W. Smith
AU - Javier Licandro
AU - Miguel R. Alarcon
PY - 2026
DA - 2026/09/07
PB - arXiv
DO - 10.48550/arxiv.2609.07404
UR - https://arxiv.org/abs/2609.07404
AB - The Emirates Mission to the Asteroid Belt (EMA) will use the MBR Explorer spacecraft to fly past six main-belt asteroids -- (10253) Westerwald, (623) Chimaera, (13294) Rockox, (88055) Ghaf, (23871) Ousha and (59980) Moza -- before rendezvousing with, and deploying a lander onto, the extremely red (269) Justitia. We present a homogeneous analysis of a decade of sparse photometry of all seven targets from the Asteroid Terrestrial-impact Last Alert System (ATLAS). For each object we derive absolute magnitudes and phase slopes in the ATLAS c and o bands, the c-o colour on a common phase slope, a rotation period from a Lomb-Scargle periodogram of the phase-corrected light curve, and a light-curve amplitude setting a lower limit on elongation. Five periods are secure -- 3.243 h for Rockox, 33.1 h for Justitia, 3.64 h for Westerwald, 14.6 h for Chimaera and 4.36 h for Moza -- and agree with independent work; for Ousha aliasing leads us to adopt the published 8.35 h, while Ghaf remains unresolved. Lightcurve inversion gives a unique convex shape and spin state for Rockox and two pole solutions for Chimaera, Moza and Justitia; no model was obtained for Ghaf, Ousha or Westerwald, though Westerwald's spin axis must be retrograde. Combining the c-o colour with an albedo class from the phase slope, we classify the sample as one dark C-type (Chimaera), three probable S-types (Westerwald, Ghaf, Moza), two X-complex objects (Rockox, plausibly M-type, and Ousha, possibly E-type), and the exceptionally red L/D-type Justitia, whose (c-o) = 0.48 is redder than typical Jupiter Trojans. This only partly matches the mission's family-based expectation of a predominantly primitive target set, so we present these as testable predictions. Those of Ghaf and Ousha are least secure -- both disagree with published work and have unresolved or aliased periods -- and warrant follow-up.
ER -