We present high-resolution near-infrared spectra taken during eight transits of 55 Cancri e, a nearby low-density super-Earth with a short orbital period (<18 hr). While this exoplanet’s bulk density indicates a possible atmosphere, one has not been detected definitively. Our analysis relies on the Doppler cross-correlation technique, which takes advantage of the high spectral resolution and broad wavelength coverage of our data, to search for the thousands of absorption features from hydrogen-, carbon-, and nitrogen-rich molecular species in the planetary atmosphere. Although we are unable to detect an atmosphere around 55 Cancri e, we do place strong constraints on the levels of HCN, NH₃, and C₂H₂ that may be present. In particular, at a mean molecular weight of 5 amu, we can rule out the presence of HCN in the atmosphere down to a volume mixing ratio (VMR) of 0.02%, NH₃ down to a VMR of 0.08%, and C₂H₂ down to a VMR of 1.0%. If the mean molecular weight is relaxed to 2 amu, we can rule out the presence of HCN, NH₃, and C₂H₂ down to VMRs of 0.001%, 0.0025%, and 0.08%, respectively. Our results reduce the parameter space of possible atmospheres consistent with the analysis of Hubble Space Telescope/WFC3 observations by Tsiaras et al. and indicate that if 55 Cancri e harbors an atmosphere, it must have a high mean molecular weight or clouds.

我们展示了在 55 Cancri e 的八次凌日期间拍摄的高分辨率近红外光谱，这是一个附近的低密度超级地球，轨道周期短（<18 小时）。虽然这颗系外行星的体积密度表明可能存在大气，但尚未明确检测到。我们的分析依赖于多普勒互相关技术，该技术利用我们数据的高光谱分辨率和宽波长覆盖范围，从富含氢、碳和氮的分子物种中搜索数千种吸收特征。行星大气。虽然我们无法探测到 55 Cancri e 附近的大气，但我们确实对 HCN、NH ₃和 C ₂ H ₂的水平施加了严格的限制这可能存在。特别是，当平均分子量为 5 amu 时，我们可以排除大气中 HCN 的存在，体积混合比 (VMR) 为 0.02%，NH ₃的体积混合比 (VMR)为 0.08%，C ₂ H ₂下降到 1.0% 的 VMR。如果平均分子量放宽到 2 amu，我们可以排除 HCN、NH ₃和 C ₂ H ₂的存在，VMR 分别为 0.001%、0.0025% 和 0.08%。我们的结果减少了可能大气的参数空间，这与 Tsiaras 等人对哈勃太空望远镜/WFC3 观测的分析一致。并指出如果 55 Cancri e 有大气层，它必须具有高平均分子量或云。