Saturn has long been the only giant planet in our solar system without any known Trojan members. In this Letter, with serendipitous archival observations and refined orbit determination, we report that 2019 UO₁₄ is a Trojan of the gas giant. However, the object is only a transient Trojan currently librating around the leading Lagrange point L ₄ of the Sun–Saturn system in a period of ∼0.7 kyr. Our N-body numerical simulation shows that 2019 UO₁₄ was likely captured as a Centaur and became trapped around L ₄ ∼ 2 kyr ago from a horseshoe co-orbital. The current Trojan state will be maintained for another millennium or thereabouts before transitioning back to a horseshoe state. Additionally, we characterize the physical properties of 2019 UO₁₄. Assuming a linear phase slope of 0.06 ± 0.01 mag deg⁻¹, the mean r-band absolute magnitude of the object was determined to be H _r = 13.11 ± 0.07, with its color measured to be consistent with that of Jupiter and Neptune Trojans and not statistically different from Centaurs. Although the short-lived Saturn Trojan exhibited no compelling evidence of activity in the observations, we favor the possibility that it could be an active Trojan. If confirmed, 2019 UO₁₄ would be marked as the first active Trojan in our solar system. We conservatively determine the optical depth of dust within our photometric aperture to be ≲10⁻⁷, corresponding to a dust mass-loss rate to be ≲1 kg s⁻¹, provided that the physical properties of dust grains resemble Centaur 29P/Schwassmann–Wachmann 1.

中文翻译：

---

2019 UO14：土星的瞬态木马


长期以来，土星一直是我们太阳系中唯一一颗没有任何已知特洛伊木马成员的巨行星。在这封信中，通过偶然的档案观测和精细的轨道确定，我们报告了 2019 UO₁₄ 是气态巨行星的特洛伊木马。然而，该天体只是一个瞬态特洛伊木马，目前在太阳-土星系统的拉格朗日点 L₄ 周围移动，周期为 ∼0.7 kyr。我们的 N 体数值模拟表明，2019 UO₁₄ 很可能是作为半人马捕获的，并在 L₄ ∼ 2 kyr 前从马蹄形共轨被困住。当前的特洛伊木马状态将再维持一千年左右，然后再转换回马蹄形状态。此外，我们还表征了 2019 UO₁₄ 的物理性质。假设线性相位斜率为 0.06 ± 0.01 等^度−1，天体的平均 r 波段绝对星等被确定为 H _r = 13.11 ± 0.07，其颜色测量与木星和海王星特洛伊木马的颜色一致，与半人马没有统计学差异。尽管短命的土星特洛伊木马在观测中没有显示出令人信服的活动证据，但我们支持它可能是一个活跃的特洛伊木马。如果得到确认，2019 UO₁₄ 将被标记为我们太阳系中第一个活跃的木马。我们保守地确定光度孔径内尘埃的光学深度为 ≲10⁻⁷，对应于尘埃质量损失率为 ≲1 kg s⁻¹，前提是尘埃颗粒的物理性质类似于 Centaur 29P/Schwassmann-Wachmann 1。