Water Cloud and Chemical Modulations in the Coldest Brown Dwarf
Abstract
We present high signal-to-noise, medium resolution (R ~ 1000), time-series JWST/NIRSpec spectra of WISE 0855 (265K), the coldest known brown dwarf. Medium resolution, time-series spectroscopy gives us the power to disentangle the effects of chemistry, temperature, and condensates on this cool world. Our observations span 11 hours with a 15 minute cadence covering 2.87 - 5.27 μm. The strongest time variable spectroscopic feature is carbon monoxide gas absorption producing modulations with a peak-to-peak amplitude up to 10\% at some wavelengths. Using principal component analysis, we show that the variations in carbon monoxide and phosphine correlate with one another. By comparing our data to atmospheric and structure models we present evidence of patchy water clouds within the atmosphere of WISE 0855. We find that variations in CO and PH3 abundances must originate from quenched atmospheric pressures while variations in water cloud thickness occurs at lower pressures.
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BibTeX
@misc{miles2026water,
title = {{Water Cloud and Chemical Modulations in the Coldest Brown Dwarf}},
author = {Brittany E. Miles and James Mang and Caroline V. Morley and Andrew J. I. Skemer and Melanie Rowland and Brianna Lacy and Genaro Suarez and Channon Visscher and Dániel Apai and Gordon Bjoraker and Aarynn L. Carter and Jacqueline K. Faherty and Jonathan J. Fortney and Nguyen Fuda and Thomas Geballe and Harshil Kothari and Mary Anne Limbach and Mark Marley and Allison M. McCarthy and Adam Schneider and Johanna Vos and Michael Cushing and Richard Freedman and Michael Line and Roxana Lupu and Emily Martin and Mikayla J. Wilson},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.20664},
eprint = {2609.20664},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.20664},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Water Cloud and Chemical Modulations in the Coldest Brown Dwarf
AU - Brittany E. Miles
AU - James Mang
AU - Caroline V. Morley
AU - Andrew J. I. Skemer
AU - Melanie Rowland
AU - Brianna Lacy
AU - Genaro Suarez
AU - Channon Visscher
AU - Dániel Apai
AU - Gordon Bjoraker
AU - Aarynn L. Carter
AU - Jacqueline K. Faherty
AU - Jonathan J. Fortney
AU - Nguyen Fuda
AU - Thomas Geballe
AU - Harshil Kothari
AU - Mary Anne Limbach
AU - Mark Marley
AU - Allison M. McCarthy
AU - Adam Schneider
AU - Johanna Vos
AU - Michael Cushing
AU - Richard Freedman
AU - Michael Line
AU - Roxana Lupu
AU - Emily Martin
AU - Mikayla J. Wilson
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.20664
UR - https://arxiv.org/abs/2609.20664
AB - We present high signal-to-noise, medium resolution (R ~ 1000), time-series JWST/NIRSpec spectra of WISE 0855 (265K), the coldest known brown dwarf. Medium resolution, time-series spectroscopy gives us the power to disentangle the effects of chemistry, temperature, and condensates on this cool world. Our observations span 11 hours with a 15 minute cadence covering 2.87 - 5.27 μm. The strongest time variable spectroscopic feature is carbon monoxide gas absorption producing modulations with a peak-to-peak amplitude up to 10\% at some wavelengths. Using principal component analysis, we show that the variations in carbon monoxide and phosphine correlate with one another. By comparing our data to atmospheric and structure models we present evidence of patchy water clouds within the atmosphere of WISE 0855. We find that variations in CO and PH_3 abundances must originate from quenched atmospheric pressures while variations in water cloud thickness occurs at lower pressures.
ER -