Composition constraints of the TRAPPIST-1 planets from their formation
Composition constraints of the TRAPPIST-1 planets from their formation
复制标题
TRAPPIST-1 行星形成过程中的成分限制
DOI：
10.1093/mnras/stad2110
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发表时间：
2023
影响因子：
4.8
通讯作者：
Steffen, Jason H.
中科院分区：
文献类型：
--
作者：
Childs, Anna C.;Shakespeare, Cody;Rice, David R.;Yang, Chao-Chin;Steffen, Jason H.
我们研究了Trappist-1(T1)行星的形成，这些行星是在月球大小的天体在冰线外部形成后不久开始形成的。我们的模型包括鹅卵石吸积和合并的质量增长、碎裂、I型迁移以及气体阻力的偏心和倾角抑制。我们追踪由尘埃凝聚代码提供的行星的组成演变，该代码跟踪各种尘埃物种在圆盘冷却时如何凝结出来。我们使用最终的行星组成来计算行星的结果半径，使用新的行星内部结构代码，并探索各种内部结构模型。我们的模型再现了T1系统的更广泛的体系结构，并限制了早期胚胎的初始水质量分数和主要难熔元素的最终相对丰度。我们发现，内部的两颗行星可能经历了巨大的撞击，行星胚胎之间的碰撞产生的碎片往往会孕育出随后通过卵石吸积生长的小行星。利用我们的组成约束，我们找到了一个两层模型的解，这是一个只由核心和地幔组成的行星，与观测到的两颗内行星b和c的体积密度相匹配。这与内行星经历的大量巨大撞击是一致的，这与最近的观测结果一致，即这些行星可能是干燥的。然而，对于剩余的大多数外部行星来说，双层模型似乎不太可能，这表明这些行星具有原始的水圈。我们的组成限制也表明，没有行星与无核的内部结构相一致。
We study the formation of the TRAPPIST-1 (T1) planets starting shortly after Moon-sized bodies form just exterior to the ice line. Our model includes mass growth from pebble accretion and mergers, fragmentation, type-I migration, and eccentricity and inclination dampening from gas drag. We follow the composition evolution of the planets fed by a dust condensation code that tracks how various dust species condense out of the disc as it cools. We use the final planet compositions to calculate the resulting radii of the planets using a new planet interior structure code and explore various interior structure models. Our model reproduces the broader architecture of the T1 system and constrains the initial water mass fraction of the early embryos and the final relative abundances of the major refractory elements. We find that the inner two planets likely experienced giant impacts and fragments from collisions between planetary embryos often seed the small planets that subsequently grow through pebble accretion. Using our composition constraints, we find solutions for a two-layer model, a planet comprised of only a core and mantle, that match observed bulk densities for the two inner planets b and c. This, along with the high number of giant impacts the inner planets experienced, is consistent with recent observations that these planets are likely desiccated. However, two-layer models seem unlikely for most of the remaining outer planets, which suggests that these planets have a primordial hydrosphere. Our composition constraints also indicate that no planets are consistent with a core-free interior structure.