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arXiv 2401.01400astro-ph.EP
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GJ 367b是一颗黑暗、炽热、无大气的亚地球行星

GJ 367b is a dark, hot, airless sub-Earth

Michael Zhang, Renyu Hu, Julie Inglis, Fei Dai, Jacob L. Bean, Heather A. Knutson, Kristine Lam, Elisa Goffo, Davide Gandolfi

AI总结:

本研究利用JWST/MIRI观测GJ 367b的中红外相位曲线,发现该亚地球行星零反照率、无热量再循环、基本无大气且已损失绝大部分初始挥发性物质。

摘要:

我们展示了由詹姆斯·韦伯空间望远镜(JWST)搭载的中红外仪器(MIRI)观测到的GJ 367b的中红外(5-12μm)相位曲线。GJ 367b是一颗炽热(平衡温度T_eq=1370 K)、密度极高(10.2±1.3 g/cm³)的亚地球行星,围绕一颗M型矮星运行,轨道周期为0.32天。我们测得其食深度为79±4 ppm,夜面行星与恒星的通量比为4±8 ppm,相对相位振幅为0.97±0.10——所有结果都与零反照率、无热量再循环的行星模型完全一致。该情况也与向东11±5度的相位偏移在2.2σ范围内相符。其发射光谱同样符合无热量再分布、邦德反照率A_B约为0.1的黑体特征,仅存在一个异常波长区间,我们将其归因于未解释的系统误差。发射光谱对表面成分的约束有限,但排除了气压大于约1巴的CO₂大气、(强还原条件下)气压大于约10毫巴的释气大气,以及(强氧化条件下)气压大于约0.01毫巴的释气大气。昼夜热量再循环的缺失意味着,对于广泛的成分范围,1巴的大气都被排除,而0.1巴的大气与观测数据相符。结合行星大部分昼面应处于熔融状态的事实,我们的JWST观测结果表明,这颗行星一定已经失去了其初始挥发性物质储量的绝大部分。

英文摘要:

We present the mid-infrared (5-12 $μ$m) phase curve of GJ 367b observed by the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST). GJ 367b is a hot (T_eq=1370 K), extremely dense (10.2 +- 1.3 g/cm^3) sub-Earth orbiting a M dwarf on a 0.32 d orbit. We measure an eclipse depth of 79 +- 4 ppm, a nightside planet-to-star flux ratio of 4 +- 8 ppm, and a relative phase amplitude of 0.97 +- 0.10 -- all fully consistent with a zero-albedo planet with no heat recirculation. Su ch a scenario is also consistent with the phase offset of 11 +- 5 degrees East to within 2.2$σ$. The emission spectrum is likewise consistent with a blackbody with no heat redistribution and a low albedo of A_B ~ 0.1, with the exception of one anomalous wavelength bin that we attribute to unexplained systematics. The emission spectrum puts few constraints on the surface composition, but rules out a CO2 atmosphere >~ 1 bar, an outgassed atmosphere >~10 mbar (under heavily reducing conditions), or an outgassed atmosphere >~0.01 mbar (under heavily oxidizing conditions). The lack of day-night heat recirculation implies that 1 bar atmospheres are ruled out for a wide range of compositions, while 0.1 bar atmospheres are consistent with the data. Taken together with the fact that most of the dayside should be molten, our JWST observations suggest the planet must have lost the vast majority of its initial inventory of volatiles.

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