A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
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DOI：
10.1038/nature16068
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发表时间：
2015-12
期刊：
影响因子：
64.8
通讯作者：
D. Sing;J. Fortney;N. Nikolov;H. Wakeford;T. Kataria;T. Evans;S. Aigrain;G. Ballester;A. Burrows;D. Deming;J. Désert;N. Gibson;G. Henry;C. Huitson;H. Knutson;A. D. Étangs;F. Pont;A. Showman;A. Vidal-Madjar;M. Williamson;P. Wilson
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文献类型：
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作者：
D. Sing;J. Fortney;N. Nikolov;H. Wakeford;T. Kataria;T. Evans;S. Aigrain;G. Ballester;A. Burrows;D. Deming;J. Désert;N. Gibson;G. Henry;C. Huitson;H. Knutson;A. D. Étangs;F. Pont;A. Showman;A. Vidal-Madjar;M. Williamson;P. Wilson
已经发现了数千颗凌日系外行星，但迄今为止，对其大气的光谱分析主要是由少数系外行星和相对较窄的波长范围（如1.1-1.7微米）的数据所主导。最近的研究表明，一些热木星系外行星在近红外光谱中的吸水特征比预测的要弱得多，，，，。水信号的低振幅可以用非常低的水丰度来解释，这可能是一个迹象，表明水在行星形成位置的原行星盘中被耗尽，但目前尚不清楚这种程度的耗尽是否真的会发生。或者，这些微弱的信号可能是云或薄雾遮挡的结果，，，，就像在一些光谱中发现的那样。在这里，我们报告了10个热木星的比较研究结果，覆盖波长范围为0.3-5微米，这使我们能够同时解决光学散射和红外分子吸收光谱。我们的结果揭示了一组不同的热木星，它们表现出从晴朗到多云的连续大气层。我们发现在光学波长和红外波长测量的行星半径之差是区分不同大气类型的有效度量。这种差异与水的光谱强度有关，因此在大气清澈的行星上可以看到强烈的吸水线，而最弱的特征与云和雾有关。这一结果有力地表明，在形成过程中，原始的水不太可能枯竭，云和雾是造成较弱光谱特征的原因。
Thousands of transiting exoplanets have been discovered, but spectral analysis of their atmospheres has so far been dominated by a small number of exoplanets and data spanning relatively narrow wavelength ranges (such as 1.1–1.7 micrometres). Recent studies show that some hot-Jupiter exoplanets have much weaker water absorption features in their near-infrared spectra than predicted,,,,. The low amplitude of water signatures could be explained by very low water abundances,,, which may be a sign that water was depleted in the protoplanetary disk at the planet’s formation location, but it is unclear whether this level of depletion can actually occur. Alternatively, these weak signals could be the result of obscuration by clouds or hazes,,,, as found in some optical spectra,,,. Here we report results from a comparative study of ten hot Jupiters covering the wavelength range 0.3–5 micrometres, which allows us to resolve both the optical scattering and infrared molecular absorption spectroscopically. Our results reveal a diverse group of hot Jupiters that exhibit a continuum from clear to cloudy atmospheres. We find that the difference between the planetary radius measured at optical and infrared wavelengths is an effective metric for distinguishing different atmosphere types. The difference correlates with the spectral strength of water, so that strong water absorption lines are seen in clear-atmosphere planets and the weakest features are associated with clouds and hazes. This result strongly suggests that primordial water depletion during formation is unlikely and that clouds and hazes are the cause of weaker spectral signatures.