2026-10-06 中国科学院（CAS）
AI-generated schematic illustration of the Flyby-Induced Second Accretion (FISA) mechanism. From left to right: capture of disk material during the stellar flyby, formation of a new disk, and secondary accretion by the planet. (Image by SHI et al.)
＜関連情報＞
- https://english.cas.cn/newsroom/research-news/202610/t20261007_1201736.shtml
- https://iopscience.iop.org/article/10.3847/2041-8213/ae984f
M型矮星の周囲に巨大惑星が形成される経路としての、フライバイによって誘発される第二次降着 Flyby-induced Second Accretion as a Pathway to Giant Planets Around M Dwarfs
Shunjing Zhao, Xian Shi, Hanlun Lei, Hongping Deng, Xing Lu, Man-To Hui, Guiyu Wang, and Jianchun Shi
The Astrophysical Journal Letters Published: 2026 August 31
DOI:10.3847/2041-8213/ae984f
Abstract
Classical pebble and core accretion theories face a severe challenge: they struggle to produce giant planets around low-mass M dwarfs, whose protoplanetary disks contain insufficient material. Yet, discoveries of such systems continue to mount. We propose flyby-induced second accretion (FISA), a new formation channel in which an M dwarf already hosting a terrestrial planet flies through a younger star’s protoplanetary disk, capturing gas and dust to build a second-generation disk. The preexisting planet then undergoes renewed pebble and gas accretion within this replenished reservoir and migrates inward to become a close-in giant. We performed hydrodynamic and core-accretion simulations to show that, under favorable encounter geometries, protoplanets around M dwarfs can grow into gas giants via this two-stage process. We apply the FISA framework to TOI-6894 b, a 0.168 Jupiter-mass planet orbiting a 0.207 solar-mass star at just 0.026 au, showing that it is a plausible outcome of such a flyby. An order-of-magnitude estimation shows that the probability for a close-in gas giant to form in an M dwarf system via the proposed disk-flyby mechanism is roughly 3 × 10−5.
