The nature and origin of free-floating planets (FFPs) are still largely unconstrained because of a lack of large homogeneous samples to enable a statistical analysis of their properties. So far, most FFPs have been discovered using indirect methods; microlensing surveys have proved particularly successful to detect these objects down to a few Earth masses^1,2. However, the ephemeral nature of microlensing events prevents any follow-up observations and individual characterization. Several studies have identified FFPs in young stellar clusters^3,4 and the Galactic field⁵ but their samples are small or heterogeneous in age and origin. Here we report the discovery of between 70 and 170 FFPs (depending on the assumed age) in the region encompassing Upper Scorpius and Ophiuchus, the closest young OB association to the Sun. We found an excess of FFPs by a factor of up to seven compared with core-collapse model predictions^6,7,8, demonstrating that other formation mechanisms may be at work. We estimate that ejection from planetary systems might have a contribution comparable to that of core collapse in the formation of FFPs. Therefore, ejections due to dynamical instabilities in giant exoplanet systems must be frequent within the first 10 Myr of a system’s life.

自由漂浮行星 (FFP) 的性质和起源在很大程度上仍然不受限制，因为缺乏大型同质样本来对其特性进行统计分析。到目前为止，大多数 FFP 都是使用间接方法发现的；微透镜测量已被证明特别成功地探测到这些物体到几个地球质量^1,2。然而，微透镜事件的短暂性阻止了任何后续观察和个体表征。几项研究已经确定了年轻星团^3,4和银河场^{5 中}的 FFP但他们的样本在年龄和来源上很小或异质。在这里，我们报告在包括上天蝎座和蛇夫座在内的区域发现了 70 到 170 个 FFP（取决于假定的年龄），这是离太阳最近的年轻 OB 协会。^{与核心塌陷模型预测6,7,8}相比，我们发现 FFP 的数量增加了多达 7 倍，这表明其他形成机制可能在起作用。我们估计，行星系统的弹射可能对FFPs形成的贡献与核心坍塌的贡献相当。因此，由于巨型系外行星系统的动态不稳定性导致的抛射必须在系统生命的前 10 Myr 内频繁出现。