Feasibility of the Phobos 1 Hypothesis for Dark Comet 1998 KY26
Abstract
The asteroid 1998 KY26 has been the subject of thorough observation, both optical and radar, from shortly following its discovery on 28 May 1998, through 2 further close apparitions in 2020 and 2024. This has previously allowed an accurate characterization of the object, including an unusually rapid spin-rate with period 5.3516 ± 0.0001 minutes, a diameter of 11 ± 2 m, and a high albedo of ∼0.52. Furthermore, the presence of significant nongravitational accelerations (NGAs), with no detectable shedding of gas or dust, has stimulated the 'dark comet' categorization, with JAXA repurposing their Hayabusa2♯ spacecraft to rendezvous with the object in 2031. We follow-up the astrodynamical evidence pointing to the possibility this may actually be the lost Soviet Phobos 1 probe, and analyse various photometry and astrometry associated with 1998 KY26 to further investigate the feasibility of this hypothesis. We find a first order approximation of the Phobos 1 spacecraft provides compelling agreement to 8 light curves of the object and further that modelling NGAs as solar radiation pressure (SRP) on a cylinder or solar panels provide significant reductions in residual of ∼11 % with respect to the 260 astrometric and radar measurements. Although an investigation of this kind cannot be conclusive, nevertheless the results here add strong weight to the Phobos 1 hypothesis, and we find no clear contradictory evidence. The spin pole in Ecliptic J2000 coordinates, calculated from photometry based on the Phobos 1 assumption is (λ,β)=(151+1−2∘,+11+12− 3∘) , where the quoted ranges represent approximate 68.3\% confidence levels.
Related
- The concept of thought forms as a consequence of the Acta Universi hypothesis on the nature of dark energy and data from the Dark Energy Spectroscopic Instrument (DESI)
- "Dark Matter" from the perspective of the Acta Universi hypothesis / "Тёмная материя" с точки зрения гипотезы Acta Universi
- Global 3D model reconstruction of Phobos integrating high-resolution imaging data from the Tianwen-1 mission
- Evidence of mafic silicates in the blue unit of Phobos: Vis-NIR analogs within the C and Xc-type asteroid taxonomy
- Infrared-to-visible albedo ratio of Phobos
BibTeX
@misc{hibberd2026feasibility,
title = {{Feasibility of the Phobos 1 Hypothesis for Dark Comet 1998 KY$_26$}},
author = {Adam Hibberd and Adam Crowl and Abraham Loeb},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.24283},
eprint = {2609.24283},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.24283},
}
RIS
TY - UNPB
TI - Feasibility of the Phobos 1 Hypothesis for Dark Comet 1998 KY_26
AU - Adam Hibberd
AU - Adam Crowl
AU - Abraham Loeb
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.24283
UR - https://arxiv.org/abs/2609.24283
AB - The asteroid 1998 KY_26 has been the subject of thorough observation, both optical and radar, from shortly following its discovery on 28 May 1998, through 2 further close apparitions in 2020 and 2024. This has previously allowed an accurate characterization of the object, including an unusually rapid spin-rate with period 5.3516 ± 0.0001 minutes, a diameter of 11 ± 2 m, and a high albedo of ∼0.52. Furthermore, the presence of significant nongravitational accelerations (NGAs), with no detectable shedding of gas or dust, has stimulated the 'dark comet' categorization, with JAXA repurposing their Hayabusa2♯ spacecraft to rendezvous with the object in 2031. We follow-up the astrodynamical evidence pointing to the possibility this may actually be the lost Soviet Phobos 1 probe, and analyse various photometry and astrometry associated with 1998 KY_26 to further investigate the feasibility of this hypothesis. We find a first order approximation of the Phobos 1 spacecraft provides compelling agreement to 8 light curves of the object and further that modelling NGAs as solar radiation pressure (SRP) on a cylinder or solar panels provide significant reductions in residual of ∼11 % with respect to the 260 astrometric and radar measurements. Although an investigation of this kind cannot be conclusive, nevertheless the results here add strong weight to the Phobos 1 hypothesis, and we find no clear contradictory evidence. The spin pole in Ecliptic J2000 coordinates, calculated from photometry based on the Phobos 1 assumption is (λ,β)=(151^+1_−2^∘,+11^+12_− 3^∘) , where the quoted ranges represent approximate 68.3\% confidence levels.
ER -