A rocky Earth-sized exoplanet with a temperate climate and relatively close to us? It seems too good to be true, but this is what Gliese 12 b could be. Simultaneously announced by Masayuki Kuzuhara, Akihiko Fukui and colleagues and by Shishir Dholakia, Larissa Palethorpe and colleagues in two papers published on the same day, Gliese 12 b promises to become a benchmark planet.

Gliese 12 b’s signal was first seen by the Transiting Exoplanets Survey Satellite (TESS), which observed its star — an M-dwarf only 12 parsecs away — between August and October 2021. The two teams employed an impressive array of other ground- and space-based telescopes to validate the planet’s presence and refine its properties via adaptive optics imaging, photometry and spectroscopy. The datasets are in good mutual agreement, showing a 0.9–1.0 Earth radii planet, possibly slightly more massive than Earth (although the uncertainties are still large: \({1.57}_{-0.75}^{+0.78}\) Earth masses), orbiting in 12.76 days around its star. Its equilibrium temperature is 287 K assuming a terrestrial albedo, setting Gliese 12 b squarely in the temperate–warm regime and just inward of the classical ‘habitable zone’.

一颗地球大小的岩石系外行星，气候温和，距离我们相对较近？这似乎好得令人难以置信，但这就是 Gliese 12 b 的可能。 Masayuki Kuzuhara、Akihiko Fukui 及其同事以及 Shishir Dholakia、Larissa Palethorpe 及其同事在同一天发表的两篇论文中同时宣布，Gliese 12 b 有望成为一颗基准行星。

Gliese 12 b 的信号首先由凌日系外行星勘测卫星 (TESS) 观测到，该卫星在 2021 年 8 月至 10 月期间观测到了它的恒星——一颗距离仅 12 秒差距的 M 矮星。两个团队使用了一系列令人印象深刻的其他地面和太空信号基于望远镜来验证行星的存在并通过自适应光学成像、光度测量和光谱学来完善其属性。数据集相互一致，显示出一颗地球半径为 0.9–1.0 的行星，质量可能比地球稍大（尽管不确定性仍然很大：\({1.57}_{-0.75}^{+0.78}\) 地球质量），绕恒星公转一周为 12.76 天。假设陆地反照率，其平衡温度为 287 K，使 Gliese 12 b 完全处于温带-温暖区域，并且位于经典“宜居带”的内部。