TOI-2195 A b: Inflated 4.16-Day Neptune Retains 109-Degree Obliquity After Losing 90 Percent of Its Mass

The Magellan/PFS Rossiter-McLaughlin time series yields a sky-projected obliquity of 109 +35/-53 degrees at 2.6-sigma . Coupled N-body plus planetary-structure integrations show that only an initial 1-2 Jupiter-mass body excited to e greater than 0.9 by the 600-au K-dwarf companion reaches periastron distances small enough for thermal-tidal mass loss to reduce it to the observed Neptune mass while inflating the radius through deposited heat. Standard high-eccentricity migration without mass loss under-predicts the radius by 30 percent and cannot produce the observed polar orbit.

The result supplies the first direct structural and dynamical link between the short-period Neptune population and Jovian progenitors, implying that a substantial fraction of the inflated hot-Neptune sample formed via the same channel rather than in-situ assembly or disk migration. Because the simulations require fine-tuned initial inclinations near 90 degrees, the occurrence rate of such objects around wide binaries becomes a testable prediction for upcoming TESS and PLATO yields.

Confirmation will require transmission spectroscopy to measure the present-day mass-loss rate and continued radial-velocity monitoring to tighten the outer-binary orbit; both datasets are scheduled for Cycle 3 JWST and Magellan.