JWST MIRI reveals a potential atmosphere on the ultra-hot rocky planet TOI-431b

@misc{smith2026jwst,
  title = {{JWST MIRI reveals a potential atmosphere on the ultra-hot rocky planet TOI-431b}},
  author = {Cole Smith and Brandon Park Coy and Megan Weiner Mansfield and Rafael Luque and Anjali A. A. Piette and Qiao Xue and Michael Zhang and Jacob L. Bean and Madison Brady and Peter Gao and Jegug Ih and Eliza M. -R. Kempton and Edwin Kite and Daniel Koll and Jaume Orell and Enric Palle},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.03029},
  eprint = {2609.03029},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.03029},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - JWST MIRI reveals a potential atmosphere on the ultra-hot rocky planet TOI-431b
AU  - Cole Smith
AU  - Brandon Park Coy
AU  - Megan Weiner Mansfield
AU  - Rafael Luque
AU  - Anjali A. A. Piette
AU  - Qiao Xue
AU  - Michael Zhang
AU  - Jacob L. Bean
AU  - Madison Brady
AU  - Peter Gao
AU  - Jegug Ih
AU  - Eliza M. -R. Kempton
AU  - Edwin Kite
AU  - Daniel Koll
AU  - Jaume Orell
AU  - Enric Palle
PY  - 2026
DA  - 2026/09/02
PB  - arXiv
DO  - 10.48550/arxiv.2609.03029
UR  - https://arxiv.org/abs/2609.03029
AB  - An open question in exoplanet science is whether rocky exoplanets extremely close in to their host stars, `lava worlds', can retain significant atmospheres. Thermal emission observations via secondary eclipse can be used to determine whether a rocky exoplanet possesses an atmosphere. It is expected that an atmosphere could increase the planet's albedo and/or redistribute heat away from the dayside, reducing the secondary eclipse depth measured. Recent eclipse observations of lava planets, rocky planets hot enough to have liquid magma surfaces, have suggested the presence of atmospheres. Here, we present a single JWST MIRI/LRS partial secondary eclipse of the lava planet TOI-431b. We measure an eclipse depth of 81 ± 16 ppm, which corresponds to a brightness temperature of 1967^+237_−253 K and a brightness temperature ratio R = 0.81±0.10, being 1.2 σ higher than the value reported by Spitzer. The observed brightness temperature ratio is 1.8σ below that of a zero-albedo, zero heat redistribution bare rock (R=1). Given that magma pools are expected to have low albedos, we find that our results are best explained by the presence of an atmosphere. Future work to measure the exact composition of TOI-431b's atmosphere and improve models of lava planet atmospheres would better constrain the nature and evolution of lava planets.
ER  -