期刊
NATURE ASTRONOMY
卷 2, 期 3, 页码 214-219出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/s41550-017-0374-z
关键词
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资金
- NASA through Space Telescope Science Institute
- European Research Council (ERC) under the European Union [336792]
- Space Telescope Science Institute Giacconi Fellowship
- NASA
- Gruber Foundation Fellowship
- ERC [336480]
- Wallonia-Brussels Federation
- Swiss National Science Foundation [PP00P2-163967]
- Simons Foundation [327127]
- ERC under the European Union [679030/WHIPLASH]
- Swiss National Science Foundation
- European Research Council (ERC) [336480] Funding Source: European Research Council (ERC)
Seven temperate Earth-sized exoplanets readily amenable for atmospheric studies transit the nearby ultracool dwarf star TRAPPIST-1 (refs (1,2)). Their atmospheric regime is unknown and could range from extended primordial hydrogen-dominated to depleted atmospheres(3-6). Hydrogen in particular is a powerful greenhouse gas that may prevent the habitability of inner planets while enabling the habitability of outer ones(6-8). An atmosphere largely dominated by hydrogen, if cloud-free, should yield prominent spectroscopic signatures in the near-infrared detectable during transits. Observations of the innermost planets have ruled out such signatures(9). However, the outermost planets are more likely to have sustained such a Neptune-like atmosphere(10,11). Here, we report observations for the four planets within or near the system's habitable zone, the circumstellar region where liquid water could exist on a planetary surface(12-14). These planets do not exhibit prominent spectroscopic signatures at near-infrared wavelengths either, which rules out cloud-free hydrogen-dominated atmospheres for TRAPPIST-1 d, e and f, with significance of 8s, 6s and 4s, respectively. Such an atmosphere is instead not excluded for planet g. As high-altitude clouds and hazes are not expected in hydrogen-dominated atmospheres around planets with such insolation(15,16), these observations further support their terrestrial and potentially habitable nature.
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