Recent studies of ultra-hot Jupiters suggested that their atmospheres could have thermal inversions due to the presence of optical absorbers such as titanium oxide (TiO), vanadium oxide (VO), iron hydride (FeH), and other metal hydride/oxides. However, it is expected that these molecules would thermally dissociate at extremely high temperatures, thus leading to featureless spectra in the infrared. KELT-9 b, the hottest exoplanet discovered so far, is thought to belong to this regime and host an atmosphere dominated by neutral hydrogen from dissociation and atomic/ionic species. Here, we analyzed the eclipse spectrum obtained using the Hubble Space Telescope’s Wide Field Camera 3 and, by utilizing the atmospheric retrieval code TauREx3, found that the spectrum is consistent with the presence of molecular species and is poorly fitted by a simple blackbody. In particular, we find that a combination of TiO, VO, FeH, and H^- provides the best fit when considering Hubble Space Telescope (HST), Spitzer, and TESS data sets together. Aware of potential biases when combining instruments, we also analyzed the HST spectrum alone and found that TiO and VO only were needed in this case. These findings paint a more complex picture of the atmospheres of ultra-hot planets than previously thought.

最近对超热木星的研究表明，由于存在光吸收剂，例如氧化钛 (TiO)、氧化钒 (VO)、氢化铁 (FeH) 和其他金属氢化物/氧化物，它们的大气层可能会发生热反转。然而，预计这些分子会在极高的温度下热解离，从而导致红外光谱无特征。KELT-9 b 是迄今为止发现的最热的系外行星，被认为属于这种状态，并拥有以来自解离和原子/离子物种的中性氢为主的大气。在这里，我们分析了使用哈勃太空望远镜的广角相机 3 获得的日食光谱，并利用大气检索代码 TauREx3，发现光谱与分子种类的存在一致，并且与简单的黑体拟合不佳。特别是，我们发现 TiO、VO、FeH 和 H 的组合^-将哈勃太空望远镜 (HST)、斯皮策和 TESS 数据集一起考虑时提供最佳拟合。意识到组合仪器时的潜在偏差，我们还单独分析了 HST 光谱，发现在这种情况下只需要 TiO 和 VO。这些发现描绘了一幅比以前想象的更复杂的超热行星大气图。