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arXiv · 2509.02734

Synchronous Rotation in the (120347) Salacia-Actaea System

Cameron Collyer·Estela Fernandez-Valenzuela·Jose Luis Ortiz·Bryan J. Holler·Benjamin Proudfoot·Nicolas Morales·Rafael Morales·Susan Benecchi·Flavia L. Rommel·Will Grundy·Darin Ragozzine
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Abstract

We report on roughly 16 years of photometric monitoring of the transneptunian binary system (120347) Salacia-Actaea which provides significant evidence that Salacia and Actaea are tidally locked to the mutual orbital period in a fully synchronous configuration. The orbit of Actaea is updated, followed by a Lomb-Scargle periodogram analysis of the ground-based photometry which reveals a synodic period similar to the orbital period and a peak-to-peak lightcurve amplitude of {\delta}m = 0.0900 {\pm} 0.0036 mag (1{\sigma} uncertainty). Incorporating archival HST photometry that resolves each component, we argue that the periodicity in the unresolved data is driven by a longitudinally varying surface morphology on Salacia, and derive a sidereal rotation period that is within 1{\sigma} of the mutual orbital period. A rudimentary tidal evolution model is invoked that suggests synchronization occurred within 1.1 Gyr after Actaea was captured/formed.

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Cameron Collyer, Estela Fernandez-Valenzuela, Jose Luis Ortiz, Bryan J. Holler, Benjamin Proudfoot, Nicolas Morales, Rafael Morales, Susan Benecchi, Flavia L. Rommel, Will Grundy, Darin Ragozzine. 2025-09-02. Synchronous Rotation in the (120347) Salacia-Actaea System. https://arxiv.org/abs/2509.02734

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