While the Ariel mission is primarily designed for the study of warm and hot objects, with an equilibrium temperature above 500 K, in this paper we want to explore a larger sample of possible colder targets. We thus investigate the detectability with Ariel of “temperate” exoplanets (with an equilibrium temperature of 400 K). We first consider the case of hydrogen-rich exoplanets (from Jupiters to sub-Neptunes) and we calculate their infrared transmission spectrum for several classes of stars. We consider the Tier 2 mode of Ariel, for which the resolving power (R = 50 for λ < 4 μm and R = 15 for λ > 4 μm) is sufficient to get information about the chemical composition of the objects. Results show that temperate Jupiters and sub-Neptunes around all types of stars from G2 to M8, with revolution periods of a few tens of days and transit durations of a few hours, could be observed with Ariel, up to distances of about 50 pc for Jupiters and 25 pc for sub-Neptunes. In the case of temperate super-Earths, we estimate that they will not be observable in the Ariel Tier 2 mode. In a study of currently available target candidates, we find one sub-Neptune (TOI-178 g) as possibly observable in Ariel’s Tier 2. This on-going study is a follow-up of “Transit spectroscopy of temperate Jupiters with ARIEL: A feasibility study” (Encrenaz et al., Exp. Astr. 46:31–44, 2018).

虽然 Ariel 任务主要是为研究平衡温度高于 500 K 的温暖和炎热物体而设计的，但在本文中，我们希望探索可能的更冷目标的更大样本。因此，我们研究了 Ariel 对“温带”系外行星（平衡温度为 400 K）的可探测性。我们首先考虑富含氢的系外行星（从木星到亚海王星）的情况，并计算它们对几类恒星的红外透射光谱。我们考虑 Ariel 的 Tier 2 模式，其分辨率（对于 λ < 4 μm，R = 50，对于 λ > 4 μm，R = 15）足以获取有关物体化学成分的信息。结果表明，从 G2 到 M8 的所有类型的恒星周围都有温带的木星和亚海王星，Ariel 的公转周期为几十天，凌日持续时间为几小时，木星的距离可达约 50 pc，海王星的距离可达 25 pc。在温带超级地球的情况下，我们估计它们在 Ariel Tier 2 模式下是无法观测到的。在对当前可用目标候选者的研究中，我们发现一个亚海王星 (TOI-178 g) 可能在 Ariel 的第 2 层中观察到。这项正在进行的研究是“温带木星与 ARIEL 的传输光谱：A可行性研究”（Encrenaz 等人，Exp. Astr. 46:31–44, 2018）。