近日，法国巴黎理工大学Yangcheng Luo团队研究了岩浆温度解释的热岩系外行星巨蟹座55的极端天气变化——云反馈。相关论文于2025年4月22日发表在《美国科学院院刊》杂志上。

对热岩系外行星巨蟹座55的观测报告称，可见光和红外波段的亮度存在显著但无法解释的变化，例如，在亚周时间尺度上，其中红外亮度温度波动约1400 K（具有数百开尔文的不确定性）。研究组提出岩浆温度-云反馈作为一种潜在的解释，它依赖于地球的大气层和表面。在这种反馈中，在无云条件下，恒星辐射加热了地表岩浆，释放出硅酸盐蒸汽凝结成云。一旦形成，这些云就会减弱恒星的日射，从而冷却表面，减少蒸汽供应，减少云量。地表温度升高和云层形成之间的时间滞后，可能是由于云层形成蒸汽的大气传输滞后造成的，这使得地表温度和云量能够自我维持振荡。

这些振荡表现为行星热发射和反射星光的变化，导致不同波长的二次日食深度的变化，而不会显著影响过境深度。使用一个简单的模型，研究组发现不同的行星参数可以再现观测到的红外亮度变化。他们还证明，不同波长的亮度可以异相振荡，这与詹姆斯·韦伯太空望远镜最近的观测结果一致。

此外，研究组提出，时变和空间不均匀的云层覆盖可能会导致行星相位曲线的振幅和相位偏移发生变化，这可能会解释观测结果。最后，他们讨论了在巨蟹座55上测试这一机制的观测策略。如果得到证实，这些可观测到的系外行星上的海洋-大气动力学将为岩石行星挥发物的组成、演化和长期命运提供有价值的见解。

附：英文原文

Title: Extreme weather variability on hot rocky exoplanet 55 Cancri e explained by magma temperature–cloud feedback

Author: Loftus, Kaitlyn, Luo, Yangcheng, Fan, Bowen, Kite, Edwin S.

Issue&Volume: 2025-4-22

Abstract: Observations of the hot rocky exoplanet 55 Cancri e report significant but unexplained variability in brightness across visible and infrared bands, e.g., on subweekly timescales, its mid-infrared brightness temperature fluctuates by approximately 1,400 K (with hundreds of Kelvin uncertainty). We propose a magma temperature–cloud feedback as a potential explanation that relies on the planet’s atmosphere and surface. In this feedback, under cloud-free conditions, stellar radiation heats surface magma, releasing silicate vapor that condenses into clouds. Once formed, these clouds attenuate stellar insolation, thereby cooling the surface, reducing vapor supply, and decreasing cloudiness. A time lag between surface temperature increase and cloud formation, likely due to lagged atmospheric transport of cloud-forming vapor, enables self-sustained oscillations in surface temperature and cloudiness. These oscillations manifest as variations in both the planet’s thermal emission and reflected starlight, causing variability in secondary eclipse depths across wavelengths without significantly affecting the transit depth. Using a simple model, we find that diverse planetary parameters can reproduce the observed infrared brightness variability. We also demonstrate that brightness at different wavelengths can oscillate out of phase, consistent with recent observations by the James Webb Space Telescope. Additionally, we propose that time-varying and spatially nonuniform cloud cover can result in changing amplitude and phase offset of the planet’s phase curve, potentially explaining observations. Finally, we discuss observational strategies to test this proposed mechanism on 55 Cancri e. If confirmed, these observable ocean–atmosphere dynamics on exoplanets would provide valuable insights into the composition, evolution, and long-term fate of rocky planet volatiles.

DOI: 10.1073/pnas.2423473122

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2423473122