Improved Constraints on the Surface of LHS 3844 b from its Mid-Infrared Spectrum
Abstract
The thermal emission spectra of terrestrial exoplanets provide a window into their surface compositions and corresponding geological processes. Close-in, rocky planets orbiting M dwarfs are ideal targets for these studies, as observations have shown that most have little to no atmosphere. LHS 3844 b is an ultra-short period super-Earth orbiting a nearby M dwarf, and is the most favorable target that does not have a dayside magma ocean. We present an updated JWST MIRI/LRS emission spectrum (5−12 μm) of this planet, derived from eight new and three archival eclipse observations. We combine these visits to obtain the highest SNR emission spectrum for any rocky exoplanet thus far, with a median SNR of 29 across 12 wavelength bins. Our data are sensitive to the predicted Si-O stretching feature (the strongest mid-infrared silicate feature) for a wide range of common materials and the transparency feature, which is relatively insensitive to composition and constrains the grain size and porosity of surface materials. We find that LHS 3844 b's emission spectrum resembles a blackbody shortward of 10 μm disfavoring the presence of a transparency feature, and identify a tentative feature (1.9−3.5σ) between 10−12 μm. If this feature is astrophysical and not instrumental in nature, it can be matched by a fayalite (the iron end-member of olivine) surface, but might also be consistent with other candidate planet-forming materials like spinel or silicon carbide. We discuss possible biases introduced by the wavelength-dependent instrumental ramp, and outline several strategies to mitigate this effect in future observations of LHS 3844~b that would establish the surface composition of this rocky exoplanet.
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BibTeX
@misc{paragas2026improved,
title = {{Improved Constraints on the Surface of LHS 3844 b from its Mid-Infrared Spectrum}},
author = {Kimberly Paragas and Heather A. Knutson and Renyu Hu and Bethany L. Ehlmann and Aishwarya R. Iyer and Sebastian Zieba and Laura Kreidberg},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2609.37982},
eprint = {2609.37982},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.37982},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Improved Constraints on the Surface of LHS 3844 b from its Mid-Infrared Spectrum
AU - Kimberly Paragas
AU - Heather A. Knutson
AU - Renyu Hu
AU - Bethany L. Ehlmann
AU - Aishwarya R. Iyer
AU - Sebastian Zieba
AU - Laura Kreidberg
PY - 2026
DA - 2026/10/05
PB - arXiv
DO - 10.48550/arxiv.2609.37982
UR - https://arxiv.org/abs/2609.37982
AB - The thermal emission spectra of terrestrial exoplanets provide a window into their surface compositions and corresponding geological processes. Close-in, rocky planets orbiting M dwarfs are ideal targets for these studies, as observations have shown that most have little to no atmosphere. LHS 3844 b is an ultra-short period super-Earth orbiting a nearby M dwarf, and is the most favorable target that does not have a dayside magma ocean. We present an updated JWST MIRI/LRS emission spectrum (5−12 μm) of this planet, derived from eight new and three archival eclipse observations. We combine these visits to obtain the highest SNR emission spectrum for any rocky exoplanet thus far, with a median SNR of 29 across 12 wavelength bins. Our data are sensitive to the predicted Si-O stretching feature (the strongest mid-infrared silicate feature) for a wide range of common materials and the transparency feature, which is relatively insensitive to composition and constrains the grain size and porosity of surface materials. We find that LHS 3844 b's emission spectrum resembles a blackbody shortward of 10 μm disfavoring the presence of a transparency feature, and identify a tentative feature (1.9−3.5σ) between 10−12 μm. If this feature is astrophysical and not instrumental in nature, it can be matched by a fayalite (the iron end-member of olivine) surface, but might also be consistent with other candidate planet-forming materials like spinel or silicon carbide. We discuss possible biases introduced by the wavelength-dependent instrumental ramp, and outline several strategies to mitigate this effect in future observations of LHS 3844~b that would establish the surface composition of this rocky exoplanet.
ER -