The TRAPPIST-1 system contains seven roughly Earth-sized planets locked in a multiresonant orbital configuration^1,2, which has enabled precise measurements of the planets’ masses and constrained their compositions³. Here we use the system’s fragile orbital structure to place robust upper limits on the planets’ bombardment histories. We use N-body simulations to show how perturbations from additional objects can break the multiresonant configuration by either triggering dynamical instability or simply removing the planets from resonance. The planets cannot have interacted with more than ~5% of one Earth mass (M_⊕) in planetesimals—or a single rogue planet more massive than Earth’s Moon—without disrupting their resonant orbital structure. This implies an upper limit of 10⁻⁴ M_⊕ to 10⁻² M_⊕ of late accretion on each planet since the dispersal of the system’s gaseous disk. This is comparable to (or less than) the late accretion on Earth after the Moon-forming impact^4,5, and demonstrates that the growth of the TRAPPIST-1 planets was complete in just a few million years, roughly an order of magnitude faster than that of the Earth^6,7. Our results imply that any large water reservoirs on the TRAPPIST-1 planets must have been incorporated during their formation in the gaseous disk.

TRAPPIST-1 系统包含七个大致地球大小的行星，它们被锁定在一个多共振轨道配置^1,2中，这使得能够精确测量行星的质量并限制它们的成分³。在这里，我们使用该系统脆弱的轨道结构为行星的轰炸历史设定了强大的上限。我们使用N体模拟来展示来自其他物体的扰动如何通过触发动态不稳定性或简单地将行星从共振中移除来破坏多共振配置。行星与一个地球质量的约 5%（M _⊕) 在小行星或比地球的月球质量更大的单个流氓行星中，而不会破坏它们的共振轨道结构。这意味着自系统气态盘分散以来，每颗行星的晚期吸积上限为 10 ^-4 M _⊕至 10 ^-2  M _{⊕ 。}这与月球形成撞击后地球上的晚期吸积相当（或更少）^4,5，并表明 TRAPPIST-1 行星的生长在短短几百万年内就完成了，大约快了一个数量级比地球^6,7。我们的结果表明，TRAPPIST-1 行星上的任何大型水库都必须在气态盘中形成过程中被合并。