一项由蒙特利尔大学领导的研究团队发现，位于宜居带的系外行星 LHS 1140 b 可能拥有大气层，表面覆盖着冰层，甚至可能存在液态水海洋。如果得到证实，这将使其成为除地球和火星外，第三颗已知在其宿主恒星宜居带内拥有大气的行星。LHS 1140 b 是一颗高度研究的系外行星，自 2017 年被发现以来，已通过多个望远镜进行了观测，包括凌日系外行星巡天卫星（TESS）、哈勃太空望远镜、斯皮策太空望远镜和欧洲南方天文台甚大望远镜上的 ESPRESSO 光谱仪。今年早些时候，这个由蒙特利尔大学领导的团队重新分析了现有观测结果，以更新和完善一系列参数，包括该行星的半径和质量。研究人员发现，其密度与纯地球岩石内核不一致，表明在岩石、富含金属的核心之上存在氢包层或水层。随后，他们利用詹姆斯·韦伯太空望远镜（JWST）上的 NIRISS（近红外成像仪和无缝光谱仪）仪器对这颗系外行星的性质进行了进一步研究，旨在区分“迷你海王星”或“水世界”情景。

🪐 蒙特利尔大学领导的研究团队发现，位于宜居带的系外行星 LHS 1140 b 可能拥有大气层，表面覆盖着冰层，甚至可能存在液态水海洋。

🔭 该团队重新分析了现有观测结果，发现其密度与纯地球岩石内核不一致，表明在岩石、富含金属的核心之上存在氢包层或水层。

🌌 研究人员利用詹姆斯·韦伯太空望远镜（JWST）上的 NIRISS（近红外成像仪和无缝光谱仪）仪器对这颗系外行星的性质进行了进一步研究，发现其大气层可能富含氮气，这与“水世界”假设一致。

🌎 如果得到证实，这将使其成为除地球和火星外，第三颗已知在其宿主恒星宜居带内拥有大气的行星。

🚀 研究人员计划利用 JWST 上的 NIRSpec（近红外光谱仪）仪器进行进一步观测，以确定该行星是否拥有大气层。

🧪 研究人员指出，明确探测到 CO2 将需要使用 JWST 进行两到三年的观测，并应提供确凿的证据证明 LHS 1140 b 是一颗拥有大量水库的超级地球。

⚠️ 研究人员指出，除了获得 JWST 观测时间外，一个关键挑战是解决传输数据中的恒星污染问题。

A research team headed up at the University of Montreal has discovered that the temperate exoplanet LHS 1140 b may have an atmosphere, could be covered in ice, and may even have an ocean of liquid water. If confirmed, this would make it only the third known planet in its host star’s habitable zone to have an atmosphere, after Earth and Mars.

Profound implications

LHS 1140 b, discovered in 2017, is a highly studied exoplanet with observations obtained by several telescopes, including the Transiting Exoplanet Survey Satellite (TESS), the Hubble Space Telescope, the Spitzer Space Telescope and the ESPRESSO spectrograph on the ESO/Very Large Telescope.

Earlier this year, the Montreal-led team reanalysed existing observations to update and refine a range of parameters, including the planet’s radius and mass. The researchers found that its density is inconsistent with a purely Earth-like rocky interior, suggesting the presence of a hydrogen envelope or a water layer atop a rocky, metal-rich core.

They then embarked on a further study of the nature of the exoplanet with the NIRISS (near-infrared imager and slitless spectrograph) instrument on the James Webb Space Telescope (JWST), aiming to distinguish between the “mini-Neptune” or “water world” scenarios.

Presenting the results in The Astrophysical Journal Letters, the astronomers describe how they studied the atmosphere of LHS 1140 b using the transmission spectroscopy technique, which involves observing a planet as it transits in front of its host star.

“Our findings indicate that LHS 1140 b’s atmosphere is not dominated by hydrogen, with the most likely scenario being a nitrogen-rich atmosphere consistent with the water world hypothesis,” says lead author Charles Cadieux, a PhD student at the University of Montreal’s Trottier Institute for Research on Exoplanets, supervised by René Doyon.

“By collecting this light at different wavelengths using a spectrograph – in this case, the NIRISS instrument on JWST – we can infer the atmospheric composition. Molecules such as H₂O, CH₄ [methane], CO, CO₂ and NH₃ [ammonia] all absorb light at specific wavelengths, allowing us to identify their presence, or absence,” Cadieux explains.

“Looking at the whole exoplanet population, no atmosphere on a rocky, terrestrial exoplanet has yet been detected to date, this is hard. Our tentative result of a nitrogen-rich atmosphere on LHS 1140 b, if firmly confirmed by additional observations, would be the first such detection,” he adds.

Cadieux notes that this discovery would place LHS 1140 b as only the third known planet with an atmosphere in the habitable zone of its host star, alongside Earth and Mars, confirming that the implications for future research are “profound” and “would provide a target for studying the habitability and the potential for life to exist on rocky, water-rich exoplanets around low-mass stars”.

Super-Earth

According to Cadieux, the next step is to repeat the observations with JWST to confirm the tentative detection of a nitrogen-rich atmosphere. While the current observations use the NIRISS instrument, the team also plans to use the NIRSpec (near infrared spectrograph) instrument on JWST, which extends further into the infrared and can probe the CO₂ content of the atmosphere.

Understanding the CO₂ content is crucial, as CO₂’s greenhouse effect controls surface temperature and the potential size of a liquid water ocean on LHS 1140 b. Cadieux notes that clear detection of CO₂ will require two to three years of observations with JWST and should provide definitive proof that LHS 1140 b is a super-Earth with a significant water reservoir.

One key challenge, besides securing JWST observation time, will be addressing stellar contamination in the transmission data. “Since LHS 1140 b orbits a smaller and cooler M-type star, stellar spots on the star’s surface can form molecules like water, which can be misinterpreted as a planetary signal,” Cadieux explains. “Even with additional data in the future, we must carefully correct for stellar contamination to ensure accurate results.”

The post Icy exoplanet found to be potentially habitable appeared first on Physics World.