Investigating potential causes for high inferred intrinsic temperatures of warm transiting Neptune and Sub-Neptune planets
Abstract
Atmospheric characterization of a warm 10-30 Myr old sub-Neptune progenitor (V1298 Tau b) and a ∼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 (∼100) for V1298 Tau b, implying an extremely short obliquity damping timescale (<104 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 ∼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.
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BibTeX
@misc{barat2026investigating,
title = {{Investigating potential causes for high inferred intrinsic temperatures of warm transiting Neptune and Sub-Neptune planets}},
author = {Saugata Barat and Jean-Michel Désert and Allona Vazan and Ritika Sethi and Sagnick Mukherjee and Sarah Millholland and Jonathan J. Fortney and William Misener and Hilke E. Schlichting and Sara Seager},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.32044},
eprint = {2609.32044},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.32044},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Investigating potential causes for high inferred intrinsic temperatures of warm transiting Neptune and Sub-Neptune planets
AU - Saugata Barat
AU - Jean-Michel Désert
AU - Allona Vazan
AU - Ritika Sethi
AU - Sagnick Mukherjee
AU - Sarah Millholland
AU - Jonathan J. Fortney
AU - William Misener
AU - Hilke E. Schlichting
AU - Sara Seager
PY - 2026
DA - 2026/09/25
PB - arXiv
DO - 10.48550/arxiv.2609.32044
UR - https://arxiv.org/abs/2609.32044
AB - Atmospheric characterization of a warm 10-30 Myr old sub-Neptune progenitor (V1298 Tau b) and a ∼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 (∼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 ∼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.
ER -