贫氦风并不需要贫氦行星
Helium-poor winds do not require helium-poor planets
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中文总结 AI 辅助
本研究提出大气过渡区输运-滞留解析理论，结合数值模型与12颗系外行星样本，证明仅输运物理过程即可导致氦贫化，无需行星本身贫氦，为系外行星大气氦丰度观测提供新解释。
中文摘要 AI 辅助
对亚稳态He I 10830埃三重线的观测揭示了正在逃逸的系外行星大气，其推断出的氦丰度范围从接近星云组成到强贫氦风不等。这类贫化通常被解释为大气演化、优先逃逸或偏离原始组成的证据。我们提出了一种针对均温层与行星风底部之间大气过渡区的闭合形式输运-滞留解析理论。该理论量化了向上输运与分子分离之间的竞争，证明仅输运物理过程就能大幅消耗供给逃逸流的氦丰度。我们的解给出了滞留因子$χ_{\rm He}$，用于衡量供给流体动力学风底部的氦占深层大气丰度的比例。将该解析框架与He I 10830埃吸收的数值正演模型以及12颗已观测到氦的亚海王星和迷你海王星样本相结合，我们发现观测到的系统覆盖了预测滞留状态的全部范围，从几乎完全滞留到强氦贫化。这些正演模型使用解析框架提供的氦丰度作为下边界条件，以预测对应的He I 10830埃吸收。我们进一步表明，提高氦滞留度会通过增加高层大气可用的氦储库，系统性地增强预期的吸收信号。这些结果表明，氦贫化并不一定意味着大气本身贫氦或向次生组成的演化转变，反而可能是逃逸大气中输运物理过程的自然结果。
英文摘要
Observations of the metastable He,{\sc i},10830,Å triplet have revealed escaping exoplanet atmospheres whose inferred helium abundances range from nearly nebular compositions to strongly helium-depleted winds. Such depletion is commonly interpreted as evidence for atmospheric evolution, preferential escape, or departures from primordial composition. We present a closed-form analytic transport-retention theory for the atmospheric transition region between the homopause and the base of the planetary wind. The theory quantifies the competition between upward transport and molecular separation, demonstrating that transport physics alone can substantially deplete the helium abundance supplied to the escaping flow. Our solution yields a retention factor, $χ_{\rm He}$, that measures the fraction of helium supplied to the base of the hydrodynamic wind relative to the deep atmospheric abundance. Combining the analytic framework with numerical forward models of the He,{\sc i},10830,Å absorption and a sample of twelve helium-observed sub-Neptunes and mini-Neptunes, we find that observed systems span the full range of predicted retention states, from nearly complete retention to strong helium depletion. These forward models use the helium abundance supplied by the analytic framework as the lower-boundary condition to predict the corresponding He,{\sc i},10830,Å absorption. We further show that increasing helium retention systematically strengthens the expected absorption signal by increasing the helium reservoir available to the upper atmosphere. These results suggest that helium depletion does not necessarily imply intrinsically helium-poor atmospheres or evolutionary transitions toward secondary compositions, but may instead be a natural consequence of transport physics in escaping atmospheres.
