木星軌道の形状は、地球上で見落とされている重要な役割を担っている Jupiter’s orbit shape plays key, overlooked role on Earth
2022-09-09 カリフォルニア大学リバーサイド校(UCR)
カリフォルニア大学リバーサイド校の研究者たちは、現在の太陽系のデータに基づいた詳細なモデルを用いて、別の太陽系を作った。その結果、巨大な木星の軌道の偏心が大きくなると、地球の軌道の形が大きく変化することがわかった。
もし木星が地球の軌道をより偏心させた場合、地球の一部は時々太陽に近づき、現在氷点下である地表の一部が暖かくなり、居住可能な範囲の気温が上昇する。
また、木星が太陽に近い位置にある場合、地球に極端な傾きが生じ、地表の大部分が氷点下になることも、同じ研究でわかっている。
＜関連情報＞
- https://news.ucr.edu/articles/2022/09/09/could-more-earths-surface-host-life
- https://iopscience.iop.org/article/10.3847/1538-3881/ac87fd
惑星系アーキテクチャと惑星傾斜角：長期居住性への示唆 System Architecture and Planetary Obliquity: Implications for Long-term Habitability
Pam Vervoort, Jonathan Horner, Stephen R. Kane, Sandra Kirtland Turner, and James B. Gilmore
Astronomical Journal Published: 2022 September 8
DOI:https://doi.org/10.3847/1538-3881/ac87fd
Abstract
In the search for life beyond our solar system, attention should be focused on those planets that have the potential to maintain habitable conditions over the prolonged periods of time needed for the emergence and expansion of life as we know it. The observable planetary architecture is one of the determinants for long-term habitability as it controls the orbital evolution and ultimately the stellar fluxes received by the planet. With an ensemble of n-body simulations and obliquity models of hypothetical planetary systems, we demonstrate that the amplitude and period of the eccentricity, obliquity, and precession cycles of an Earth-like planet are sensitive to the orbital characteristics of a giant companion planet. A series of transient, ocean-coupled climate simulations show how these characteristics of astronomical cycles are decisive for the evolving surface conditions and long-term fractional habitability relative to the modern Earth. The habitability of Earth-like planets increases with the eccentricity of a Jupiter-like companion, provided that the mean obliquity is sufficiently low to maintain temperate temperatures over large parts of its surface throughout the orbital year. A giant companion closer in results in shorter eccentricity cycles of an Earth-like planet but longer, high-amplitude, obliquity cycles. The period and amplitude of obliquity cycles can be estimated to first order from the orbital pathways calculated by the n-body simulations. In the majority of simulations, the obliquity amplitude relates directly to the orbital inclination whereas the period of the obliquity cycle is a function of the nodal precession and the proximity of the giant companion.
