Gaia Mission Reveals New Binary Asteroid Candidates Through Stellar Occultation Study
A large international team of astronomers has identified four asteroid systems showing signs of binary or contact-binary structure — 1127 Mimi, 35420 1998 AG6, 206 Hersilia, and 36882 2000 SW155 — through a campaign of 165 stellar occultation observations conducted between October 2023 and February 2026. The work is part of the GaiaMoons program, which leverages high-precision astrometric data from the ESA Gaia mission to identify candidate binary asteroids in the main belt that conventional detection methods tend to miss. Characterizing binary asteroids is scientifically important because their orbital dynamics allow direct measurement of masses and densities, providing fundamental constraints on Solar System formation and planetary evolution.
The GaiaMoons program, presented in a preprint submitted to arXiv on June 11, 2026, used stellar occultations to follow up on 357 binary asteroid candidates flagged by the Gaia mission's high-precision astrometry. Out of 165 successful observations covering 101 targets, 33 events yielded at least two positive detections across 24 objects, with four — 1127 Mimi, 35420 1998 AG6, 206 Hersilia, and 36882 2000 SW155 — showing features consistent with binary or contact-binary configurations. The study addresses a known observational bias in binary asteroid science: existing techniques tend to favor either widely separated pairs or close, bright systems, leaving the main belt poorly characterized. Gaia's astrometric signatures of unresolved companions opened a new discovery channel, and the occultation method provides complementary size, shape, and astrometric constraints unavailable from other approaches. The authors note that the resulting dataset is unprecedented for the vast majority of these objects, most of which had never previously been observed via stellar occultations. The program is described as a self-improving cycle, in which occultation results refine Gaia-based predictions and guide future observing campaigns. The paper is currently a preprint and has not yet undergone formal peer review.
What's missing
The preprint has not yet been peer-reviewed, so the binary classifications for the four candidate systems remain provisional. The paper does not report confirmed orbital parameters (periods, separations, mass ratios) for the four flagged systems, leaving their binary nature as indicative rather than definitive.
What different sources said
- arXiv astro-phCenter
Detection and characterisation of binary asteroid candidates through stellar occultations
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