Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
Nature. 2016 Sep 1;537(7618):69-72. doi: 10.1038/nature18641. Epub 2016 Jul 20.
Three Earth-sized exoplanets were recently discovered close to the habitable zone of the nearby ultracool dwarf star TRAPPIST-1 (ref. 3). The nature of these planets has yet to be determined, as their masses remain unmeasured and no observational constraint is available for the planetary population surrounding ultracool dwarfs, of which the TRAPPIST-1 planets are the first transiting example. Theoretical predictions span the entire atmospheric range, from depleted to extended hydrogen-dominated atmospheres. Here we report observations of the combined transmission spectrum of the two inner planets during their simultaneous transits on 4 May 2016. The lack of features in the combined spectrum rules out cloud-free hydrogen-dominated atmospheres for each planet at ≥10σ levels; TRAPPIST-1 b and c are therefore unlikely to have an extended gas envelope as they occupy a region of parameter space in which high-altitude cloud/haze formation is not expected to be significant for hydrogen-dominated atmospheres. Many denser atmospheres remain consistent with the featureless transmission spectrum-from a cloud-free water-vapour atmosphere to a Venus-like one.
最近，在附近的极冷矮星 TRAPPIST-1（参考文献 3）附近发现了三颗大小与地球相当的系外行星。这些行星的性质尚未确定，因为它们的质量仍未测量，而且对于围绕极冷矮星的行星群，没有可观测的限制，而 TRAPPIST-1 行星就是第一个过境的例子。理论预测涵盖了整个大气范围，从贫氢到扩展的氢主导大气。在这里，我们报告了 2016 年 5 月 4 日两个内行星同时凌日时的组合传输光谱观测结果。组合光谱中没有特征排除了每颗行星在 ≥10σ 水平上无云的氢主导大气;因此，TRAPPIST-1 b 和 c 不太可能有扩展的气体包层，因为它们占据了一个参数空间区域，在这个区域中，对于氢主导大气来说，高空云/霾的形成预计不会显著。许多更密集的大气与无特征的传输光谱仍然一致——从无云的水蒸气大气到类似金星的大气。
