Impacts of Correlated Noise on Retrievals of Exo-Earth Atmospheres

Abstract

The Habitable Worlds Observatory (HWO) aims to accomplish high-contrast imaging and spectroscopy of true Earth analogs for the first time. However, high-contrast spectroscopy with HWO may be limited by residual speckles, which persist after deformable mirror correction and postprocessing, hindering atmospheric characterization. Previous studies of self-luminous giant planets showed that neglecting spectrally correlated errors due to speckles results in biased inferences of planetary parameters. Currently, HWO retrieval studies generate spectra without noise spectral correlations. We present a Gaussian process model of correlated noise of known properties in simulated HWO exo-Earth spectra, and the integration of this noise source into the forward and inverse modeling tool rfast . We quantify the impact of correlated noise on inferred molecular abundances and planetary properties across the ultraviolet/visible/near-infrared bandpass, for varying spectral resolutions ( R ), signal-to-noise ratios (SNR), and noise correlation length scales ( L ). We find that, at the fiducial UV/Vis/NIR R = 7/140/70 and SNR = 10, including spectrally correlated noise at L = 200 nm and L = 10 nm yields a 57% and 161% higher average uncertainty on log oxygen abundance, compared to uncorrelated noise. Consequently, it is critical for both instrument design and postprocessing algorithms to minimize short length-scale chromaticity. Additionally, we find that a moderate resolution can constrain carbon dioxide ( R ≥ 280) and weakly detect methane ( R ≥ 2800) abundances, demonstrating the benefit of a moderate resolution near-infrared spectrograph. These findings can aid the interpretation of future HWO reflectance spectra and set requirements on optical quality, instrument stability, and observing configurations.

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BibTeX RIS

BibTeX

@article{wolff2026impacts,
  title = {{Impacts of Correlated Noise on Retrievals of Exo-Earth Atmospheres}},
  author = {Nicole Wolff and Bruce Macintosh and Tyler D. Robinson and Sarah Blunt and Jean-Baptiste Ruffio and Beck Dacus and Alex Madurowicz and Marshall Perrin and Laurent Pueyo},
  journal = {The Astronomical Journal},
  year = {2026},
  month = sep,
  doi = {10.3847/1538-3881/ae9d67},
  url = {https://iopscience.iop.org/article/10.3847/1538-3881/ae9d67},
  note = {CC BY 4.0},
}

RIS

TY  - JOUR
TI  - Impacts of Correlated Noise on Retrievals of Exo-Earth Atmospheres
AU  - Nicole Wolff
AU  - Bruce Macintosh
AU  - Tyler D. Robinson
AU  - Sarah Blunt
AU  - Jean-Baptiste Ruffio
AU  - Beck Dacus
AU  - Alex Madurowicz
AU  - Marshall Perrin
AU  - Laurent Pueyo
PY  - 2026
DA  - 2026/09/30
JO  - The Astronomical Journal
DO  - 10.3847/1538-3881/ae9d67
UR  - https://iopscience.iop.org/article/10.3847/1538-3881/ae9d67
AB  - The Habitable Worlds Observatory (HWO) aims to accomplish high-contrast imaging and spectroscopy of true Earth analogs for the first time. However, high-contrast spectroscopy with HWO may be limited by residual speckles, which persist after deformable mirror correction and postprocessing, hindering atmospheric characterization. Previous studies of self-luminous giant planets showed that neglecting spectrally correlated errors due to speckles results in biased inferences of planetary parameters. Currently, HWO retrieval studies generate spectra without noise spectral correlations. We present a Gaussian process model of correlated noise of known properties in simulated HWO exo-Earth spectra, and the integration of this noise source into the forward and inverse modeling tool rfast . We quantify the impact of correlated noise on inferred molecular abundances and planetary properties across the ultraviolet/visible/near-infrared bandpass, for varying spectral resolutions ( R ), signal-to-noise ratios (SNR), and noise correlation length scales ( L ). We find that, at the fiducial UV/Vis/NIR R = 7/140/70 and SNR = 10, including spectrally correlated noise at L = 200 nm and L = 10 nm yields a 57% and 161% higher average uncertainty on log oxygen abundance, compared to uncorrelated noise. Consequently, it is critical for both instrument design and postprocessing algorithms to minimize short length-scale chromaticity. Additionally, we find that a moderate resolution can constrain carbon dioxide ( R ≥ 280) and weakly detect methane ( R ≥ 2800) abundances, demonstrating the benefit of a moderate resolution near-infrared spectrograph. These findings can aid the interpretation of future HWO reflectance spectra and set requirements on optical quality, instrument stability, and observing configurations.
SN  - 0004-6256
SN  - 1538-3881
ER  -

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