The origin of close-in giant planets (e.g., hot Jupiters) is the most enduring problem in the exoplanetary science. A promising approach to solve this problem is to measure the angle of host star’s spin with respect to the planetary orbital axis (so-called “stellar obliquity"), but until recently measurements of the stellar obliquity have been principally limited to relatively old stars (>∼ 100 Myr). Here, we propose Subaru/IRD observations of spectroscopic transits of IRAS 04125+2902b, which is a newly discovered infant giant planet (Rp≈ 1 RJup, P≈ 8.83 days) transiting a T-Tauri star (Teff≈ 3900 K) in the Taurus-Auriga association. Its estimated age of 3.3−0.5+0.6 Myr makes IRAS 04125+2902b by far the youngest transiting planet known to date. IRAS 04125+2902 is also known to have a “face-on" transitional disk, suggesting that the orbit of the transiting planet may be significantly misaligned with respect to the protoplanetary disk in which it formed. Given that the timescale of tidal spin-orbit “realignment" for hot Jupiters is much longer than the age of the system, the system should preserve the primordial stellar obliquity before it is affected by subsequent tidal interactions.
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