Orbits of very distant asteroid satellites

The very wide binary asteroid (VWBA) population is a small subset of the population of known binary and multiple asteroids made of systems with very distant satellites and long orbital periods, on the order of tens to hundreds of days. The origin of these systems is debatable, and most members of this population are poorly characterized.

 

Most members of this class were discovered by direct imaging, through general surveys or targeted studies of asteroid families (Merline et al. 2002, 2003a,b, 2004; Tamblyn et al. 2004), and several potential members of this class have been predicted through lightcurve studies (Warner & Stephens 2019).
In 2012, (2577) Litva became the first member of these predicted VWBA systems to be confirmed by direct imaging (Merline et al. 2013a,b).
Analysis of asteroid observations in recent surveys  (with PanSTARRS and ESA Gaia, Ou et al. 2022; Liberato et al. 2024), and evidence in cratering records (Herrera et al. 2024) indicate that this population may be substantial, but this has yet to be confirmed by observations.

 

 In our recent work (Minker et al. 2025), we aimed to study the known members of this unique group. To do so, we developed orbital solutions for some members of the VWBA population, allowing us to constrain possible formation pathways for this unusual population. We compiled all available high-angular-resolution imaging archival data of VWBA systems from large ground- and space-based telescopes, including the Keck, Gemini, Very Large, Large Binocular, and Hubble Space Telescopes. Images were reduced with standard calibration techniques, as well as halo-reduction algorithms to improve the visibility of the satellite (see Fig. 1). We measured the astrometric positions of the satellite relative to the primary at each epoch and analyzed the dynamics of the satellites using the Genoid genetic algorithm (Vachier et al. 2012). 

 

We determined new orbital solutions for five systems, (379) Huenna, (2577) Litva, (3548) Eurybates, (4674) Pauling, and (22899) Alconrad. We find a significantly eccentric (e=0.30) best-fit orbital solution for the outer satellite of (2577) Litva, moderately eccentric (e=0.13) solutions for (22899) Alconrad, and a nearly circular solution for (4674) Pauling (e=0.04). We also confirmed previously reported orbital solutions for (379) Huenna and (3548) Eurybates (Vachier et al. 2022 and Brown et al. 2021, respectively).
   

 It is unlikely that BYORP expansion could be solely responsible for the formation of VWBAs, as only (4674) Pauling matches the necessary requirements for active BYORP expansion. It is possible that the satellites of these systems were formed through YORP spin-up and then later scattered onto very wide orbits. Additionally, we find that some members of the population are unlikely to have formed satellites through YORP spin-up, and a collisional formation history  (escaping ejecta model, see Durda et al. 2004) is favored. In particular, this applies to VWBAs within large dynamical families, such as (22899) Alconrad and (2577) Litva, or large VWBA systems such as (379) Huenna and NASA's Lucy mission target (3548) Eurybates. The extremely limited observational datasets limit our current understanding of this population. In the future, utilizing unconventional observational techniques such as speckle interferometry (Aristidi et al. 2023) or indirect methods, such as detection through Gaia astrometry (Liberato et al. 2024) could contribute to the study and discovery of these objects.

 

Although the binary systems discussed in this work exhibit substantial dynamical diversity, their spin properties are globally inconsistent with those of the candidate VWBAs proposed in various works by Warner et al. (e.g. Warner & Stephens 2020, 2019; Warner 2016). However, some members of the Warner et al. population bare a resemblance to the report sensing properties of former Lucy mission target (152830) Dinkinesh, which was found during flyby to have a contact-binary satellite - suggesting that perhaps these objects are not very wide binary asteroids, but asteroids with very wide satellites!

 

 

Figure 1: Observation of (4674) Pauling, before and after the application of halo-subtraction algorithms.

References:

Aristidi, E., Carry, B., Minker, K., et al. 2023, MNRS,  524, 4

Brown, M. E., Levison, H. F., Noll, K. S., et al. 2021, Pla. Sci. Journal, 2, 170

Durda, D. D., Bottke, W. F., Enke, B. L., et al. 2004, Icarus, 167, 382

Herrera, C., Carry, B., Lagain, A., & Vavilov, D. E. 2024, A&A, 688, A176

Merline, W. J., Close, L. M., Siegler, N., et al. 2002, IAU Circ., 7827, 2

Merline, W. J., Close, L. M., Tamblyn, P. M., et al. 2003a, IAU Circ., 8075, 2

Merline, W. J., Tamblyn, P. M., Chapman, C. R., et al. 2003b, IAU Circ., 8232, 2

Merline, W. J., Tamblyn, P. M., Dumas, C., et al. 2004, IAU Circ., 8297, 1

Merline, W. J., Tamblyn, P. M., Warner, B. D., et al. 2013a, IAU Circ., 9267, 1

Merline, W. J., Tamblyn, P. M., Warner, B. D., et al. 2013b, Central Bureau Electron. Telegrams, 3765, 1

Minker, K., Carry, B., Vachier, F., et al., 2025 A&A, in press.

Ou, J., Baranec, C., & Bus, S. J. 2022, Pla. Sci. Journal, 3, 169

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Vachier, F., Berthier, J., & Marchis, F. 2012, A&A, 543, A68

Vachier, F., Carry, B., & Berthier, J. 2022, Icarus, 382, 115013

Warner, B. D. 2016, Minor Planet Bull., 43, 306 Warner, B. D., & Stephens, R. D. 2019, Minor Planet Bull., 46, 153

Warner, B. D., & Stephens, R. D. 2020, Minor Planet Bull., 47, 37