Investigating potential causes for high inferred intrinsic temperatures of warm transiting Neptune and Sub-Neptune planets

Atmospheric characterization of a warm 10-30 Myr old sub-Neptune progenitor (V1298 Tau b) and a about 3.4 Gyr old warm super-Neptune (WASP-107b) using JWST have revealed extremely low methane abundance. Atmospheric forward models find higher than expected inferred intrinsic temperatures (450 K and 500 K) --- inconsistent with theoretical planet formation and core-envelope evolution predictions (70K and 150K respectively) assuming a convective interior. We explore three hypotheses to reconcile the high intrinsic temperatures with evolutionary models --- tidal heating, silicate rainout and heat trapping due to deep cloud condensation. Tidal heating requires high planetary obliquity (70) and low reduced tidal quality factor (about 100) for V1298 Tau b, implying an extremely short obliquity damping timescale (< 10 4 years). Although high obliquity may be maintained by spin--orbit resonant locking, it requires fine-tuning and is therefore unlikely. Silicate rainout can increase the temperature in the deep atmosphere of the young V1298 Tau b (0.1-1 bar) by about 700K, without requiring extremely high intrinsic temperature, but is unlikely to explain WASP-107b, as silicate rainout timescales are expected to be much shorter than its age. Including cloud condensation in self-consistent atmospheric models reduces the inferred intrinsic temperature for V1298 Tau b from 500K to 300K, still exceeding the core-envelope prediction (150K). Future measurements of thermal emission from young transiting planets such as V1298 Tau b, combined with methane abundances as a function of age, will be needed to distinguish between these scenarios.