Possible Hycean conditions in the sub-Neptune TOI-270 d
Possible Hycean conditions in the sub-Neptune TOI-270 d
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DOI：
10.1051/0004-6361/202348238
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发表时间：
2024-03
期刊：
影响因子：
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通讯作者：
M. Holmberg;N. Madhusudhan
中科院分区：
文献类型：
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作者：
M. Holmberg;N. Madhusudhan
JWST开创了温带低质量系外行星大气特征的新时代，最近在候选海洋世界K2-18 B中探测到了含碳分子。我们调查了TOI-270系统的JWST观测，在访问期间，两个亚海王星同时穿过附近的M矮星。我们报告了我们对外行星TOI-270 d（一个候选海洋世界）的大气特征，使用NIRSpec G395 H仪器在2.7-5.2 μm范围内使用JWST透射光谱，结合HST WFC 3光谱仪（1.1-1.6 μm）获得的先前观测结果。光谱显示出CH 4和CO2的强烈特征，置信度分别为3.8-4.9σ和2.9-3.9σ，没有NH3的证据。丰富的甲烷和二氧化碳，在0.1-1%的混合比，和NH3的未检测到的K2-18 B报告的调查结果相似，并与海洋世界的预测与全球范围的海洋下的H2-丰富的大气层。根据数据分析方法，我们还报告了CS2在2.3-3.0σ置信度下的证据和H2O在1.6-4.4σ的潜在推断，并讨论了这些结果的可能解释。光谱没有提供强有力的限制云或薄雾在可观测的大气中的存在，也没有任何证据恒星的不均匀性的影响，这是与以前的研究一致。对于较小的内行星TOI-270 B，我们发现它的光谱与在103 σ处的无特征光谱不一致，表明在超级地球中有一些富含H2的大气。我们讨论了我们的研究结果和未来前景的影响。
The JWST has ushered in a new era in atmospheric characterisations of temperate low-mass exoplanets with recent detections of carbon-bearing molecules in the candidate Hycean world K2-18 b. We investigated JWST observations of the TOI-270 system, with two sub-Neptunes simultaneously transiting the nearby M dwarf during the visit. We report our atmospheric characterisation of the outer planet TOI-270 d, a candidate Hycean world, with JWST transmission spectroscopy using the NIRSpec G395H instrument in the 2.7–5.2 μm range, combined with previous observations obtained with the HST WFC3 spectrograph (1.1–1.6 μm). The spectrum reveals strong signatures of CH4 and CO2 at 3.8–4.9σ and 2.9–3.9σ confidence, respectively, and no evidence of NH3. The abundant CH4 and CO2, at ∼0.1–1% mixing ratios, and the non-detection of NH3 are similar to the findings reported for K2-18 b and consistent with predictions for a Hycean world with a planet-wide ocean under a H2-rich atmosphere. We also report evidence of CS2 at a 2.3–3.0σ confidence and a potential inference of H2O at 1.6–4.4σ, depending on the data analysis approach, and discuss possible interpretations of these results. The spectrum does not provide strong constraints on the presence of clouds or hazes in the observable atmosphere, nor any evidence for the effects of stellar heterogeneities, which is consistent with previous studies. For the smaller inner planet TOI-270 b, we find that the spectrum is inconsistent with a featureless spectrum at ∼3σ, showing some preference for an H2-rich atmosphere in a super-Earth. We discuss the implications of our findings and future prospects.