2021AJ....162...51I

Recently, it has been shown that rocky planets orbiting neutron stars can be habitable under plausible circumstances. If a distant, point-like source of visible light, such as a Sun-like main-sequence star or the gravitationally-lensed accretion disk of a supermassive black hole is present, possible temporal variations Δε_p(t) of the planet's axial tilt ε_p to the ecliptic plane should be included in the overall habitability budget since the obliquity determines the insolation at a given latitude on a body' s surface. I point out that, for rather generic initial spin-orbit initial configurations, general relativistic and classical spin variations induced by the post-Newtonian de Sitter and Lense-Thirring components of the field of the host neutron star and by its pull to the planetary oblateness J₂^p may induce huge and very fast variations of ε_p that would likely have an impact on the habitability of such worlds. In particular, for a planet's distance of, say, 0.005 au from a 1.4 M_☉ neutron star corresponding to an orbital period P_b = 0.109 day, obliquity shifts Δε_p as large as ε_p^{max}^–εp_^{min}^≃50^○–¹⁰⁰○^ over characteristic timescales as short as 10 days (J₂^p) to 3 Myr (Lense-Thirring) may occur for arbitrary orientations of the orbital and spin angular momenta L, S_ns, S_p of the planet-neutron star system. In view of this feature of their spins, I dub such hypothetical planets as "nethotrons."