Astronomers have found more than a dozen planets transiting stars that are 10–40 million years old¹, but younger transiting planets have remained elusive. The lack of such discoveries may be because planets have not fully formed at this age or because our view is blocked by the protoplanetary disk. However, we now know that many outer disks are warped or broken²; provided the inner disk is depleted, transiting planets may thus be visible. Here we report observations of the transiting planet IRAS 04125+2902 b orbiting a 3-million-year-old, 0.7-solar-mass, pre-main-sequence star in the Taurus Molecular Cloud. The host star harbours a nearly face-on (30 degrees inclination) transitional disk³ and a wide binary companion. The planet has a period of 8.83 days, a radius of 10.7 Earth radii (0.96 Jupiter radii) and a 95%-confidence upper limit on its mass of 90 Earth masses (0.3 Jupiter masses) from radial-velocity measurements, making it a possible precursor of the super-Earths and sub-Neptunes frequently found around main-sequence stars. The rotational broadening of the star and the orbit of the wide (4 arcseconds, 635 astronomical units) companion are both consistent with edge-on orientations. Thus, all components of the system are consistent with alignment except the outer disk; the origin of this misalignment is unclear.

天文学家已经发现了十几颗行星凌日恒星，这些恒星的年龄为 10-4000 万年¹，但更年轻的凌日行星仍然难以捉摸。缺乏这样的发现可能是因为行星在这个年龄还没有完全形成，或者因为我们的视野被原行星盘挡住了。然而，我们现在知道很多外盘翘曲或断裂²;如果内盘耗尽，则可以看到凌日行星。在这里，我们报告了对凌日行星 IRAS 04125+2902 b 的观测，该行星围绕金牛座分子云中一颗 300 万年历史、0.7 太阳质量的前主序星运行。这颗宿主恒星有一个几乎正面（30度倾角）的过渡盘³和一个宽的双星伴星。这颗行星的周期为 8.83 天，半径为 10.7 个地球半径（0.96 个木星半径），径向速度测量的 90 个地球质量（0.3 个木星质量）的质量上限为 95%，使其成为主序星周围经常发现的超级地球和亚海王星的前身。恒星的旋转展宽和宽（4 角秒，635 天文单位）伴星的轨道都与边朝一致。因此，除外盘外，系统的所有组件都与 alignment 一致;这种错位的根源尚不清楚。