Kepler-9, discovered by Holman et al. 2010, was the first system with multiple confirmed transiting planets and the first system to clearly show long-anticipated transit timing variations (TTVs). We review the historical circumstances behind the discovery and characterization of these planets and the publication of Holman et al. 2010. It was the first major novel exoplanet discovery of the Kepler Space Telescope mission. The Kepler pipeline identified two Saturn-radius candidates (called Kepler Objects of Interest or KOIs): KOI-377.01 with a 19-day period and KOI-377.02 with a 39-day period. Even with only 9 transits for KOI-377.01 and 6 of KOI-377.02, the transit times were completely inconsistent with a linear ephemeris and showed strongly anti-correlated variations in transit times. Holman et al. 2010 were able to readily show that these objects were planetary mass, confirming them as bona fide planets Kepler-9b and Kepler-9c. As a multi-transiting system exhibiting strong TTVs, the relative planetary properties (e.g., mass ratio, radius ratio) were strongly constrained, opening a new chapter in comparative planetology. KOI-377.03, a small planet with a 1.5-day period, was not initially discovered by the Kepler pipeline, but was identified during the analysis of the other planets and was later confirmed as Kepler-9d through the BLENDER technique by Torres et al. 2011. Holman et al. 2010 included significant dynamical analysis to characterize Kepler-9's particular TTVs: planets near resonance show large amplitude anti-correlated TTVs with a period corresponding to the rotation of the line of conjunctions and an additional "chopping" signal due to the changing positions of the planets. We also review the updated properties of this system and propose ideas for future investigations.

中文翻译：

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Kepler-9：第一个多中转系统和第一个中转时间变化

由 Holman 等人发现的 Kepler-9。2010 年是第一个确认有多个凌日行星的系统，也是第一个明确显示长期预期凌日时间变化 (TTV) 的系统。我们回顾了这些行星的发现和特征以及 Holman 等人的出版物背后的历史环境。2010. 这是开普勒太空望远镜任务的第一个主要的新型系外行星发现。开普勒管道确定了两个土星半径候选对象（称为开普勒感兴趣对象或 KOI）：19 天周期的 KOI-377.01 和 39 天周期的 KOI-377.02。即使只有 9 次 KOI-377.01 和 6 次 KOI-377.02 过境，其过境时间也与线性星历完全不一致，并且过境时间显示出强烈的反相关变化。霍尔曼等人。2010 年能够很容易地证明这些物体是行星质量，确认它们是真正的行星 Kepler-9b 和 Kepler-9c。作为一个表现出强 TTV 的多凌日系统，行星的相关属性（如质量比、半径比）受到强烈限制，开启了比较行星学的新篇章。KOI-377.03 是一颗周期为 1.5 天的小行星，最初并未被开普勒管道发现，但在对其他行星的分析中被识别出来，后来被托雷斯等人通过 BLENDER 技术确认为开普勒 9d。2011. 霍尔曼等人。2010 年包括重要的动力学分析来表征 Kepler-9 的特定 TTV：共振附近的行星显示大振幅反相关 TTV，其周期对应于连接线的旋转和一个额外的“