TOI-4129 b at the Neptune ridge’s inner edge

How it fits

A 2 November 2026 arXiv preprint reports confirmation of TOI-4129 b, a TESS candidate flagged in 2021. The team combines TESS and ground-based transits with 25 HARPS-N measurements of the star’s wobble. Their joint fit gives it a 3.27-day orbit, a radius of 5.7 ± 0.2 Earth radii and a mass of 26 ± 6 Earth masses.[1]

The Neptune ridge is a concentration of Neptune-sized planets with periods around 3.2–5.7 days. At 3.27 days, TOI-4129 b sits near its inner edge. Many Neptune-ridge candidates detected by TESS remain unconfirmed, and this one mass-measured example cannot by itself explain how the ridge formed.[1]

The 1.2-billion-year age estimate uses stellar rotation; other dating methods are inconclusive, and these stars may not slow steadily. The record says resubmitted to AJ, with no acceptance listed.[1]