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Abstract Recent large-scale transit surveys conducted by space telescopes such as Kepler and TESS have revealed a vast number of exoplanets, uncovering the diversity of their population. One of the remarkable findings is the presence of a deficiency region in the period–radius distribution of short-period (10 d) Neptune-sized planets (4–8 R_). This region is classified into the Neptune desert (3. 2 d), the ridge (3. 2–5. 7 d), and the savanna (5. 7 d) based on orbital period, each likely reflecting distinct evolutionary pathways. In this study, we used the InfraRed Doppler (IRD) instrument on the Subaru Telescope to determine the mass of the super-Neptune TOI-1883 b, which resides in the ridge region (P 4. 51~ d) orbiting an M dwarf. We measured a planetary mass of Mₚ = 13. 7^+6. 8-₆. ₅\, M_ and a mean density of ₚ = 0. 4^+0. 3-₀. ₂\, g\, cm^-3, with 3 upper limits of 34. 1~M_, and 5 upper limits of 47. 7~M_. These results suggest that TOI-1883 b is likely a low-density super-Neptune. We also find that the boundary of the Neptune desert defined by planets orbiting FGK-type stars exhibits a similar distribution for planets around M-type stars. According to the population-based argument of Bourrier et al. (2025, A 140), making it an excellent target for future atmospheric characterization via transmission spectroscopy.
Fukuda et al. (Wed,) studied this question.