Observing Spatial And Temporal Variations In The Atmospheric Chemistry Of Rocky Exoplanets: Prospects For Mid-infrared Spectroscopy

Future telescopes such as the Large Interferometer For Exoplanets (LIFE) will enable mid-infrared characterisation of the atmospheres of nearby rocky exoplanets.

Whilst 4D spatial and temporal variations of Earth as an exoplanet are below spectroscopic detection limits, such variability is planet-specific. We investigate LIFE’s ability to detect 4D variability in the atmospheres of tidally locked exoplanets.

We create daily synthetic LIFE observations of Proxima Centauri b in a 1:1 and an eccentric 3:2 spin-orbit resonance (SOR), using LIFEsim on spectra from daily 3D climate-chemistry model output of an aquaplanet with Earth-like composition. Hemispheric distributions of temperature, clouds, and chemical species determine spectral signatures and variability with orbital phase angle.

Such variability dictates the extent to which parameters can be reliably inferred from snapshot spectra at arbitrary viewing geometries. In the 1:1 SOR, MIR spectra vary significantly with viewing geometry and indirectly probe atmospheric circulation. Nightside temperature inversions generate O₃, CO₂, and H₂O emission features, though these lie below LIFE’s detection threshold, and instead O₃ features disappear at certain phase angles.

In contrast, the 3:2 SOR yields a more homogeneous atmosphere with weaker phase variability but enhanced bolometric flux due to eccentric heating. Phase-resolved LIFE observations confidently distinguish between the SORs and capture seasonal O₃ variability for golden targets like Proxima Centauri b.

In case of abiotic O2/O₃ build-up, the O₃ variability presents a potential false positive scenario. Hence, LIFE can disentangle different spin-orbit states and resolve 4D atmospheric variability, enabling daily characterisation of the 4D physical and chemical state of nearby terrestrial worlds. Importantly, this characterisation requires phase-resolved rather than snapshot spectra.

Marrick Braam, Daniel Angerhausen

Comments: 15 pages, 9 figures, resubmitted version for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2512.16619 [astro-ph.EP] (or arXiv:2512.16619v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2512.16619
Focus to learn more
Submission history
From: Marrick Braam
[v1] Thu, 18 Dec 2025 14:57:47 UTC (1,400 KB)
https://arxiv.org/abs/2512.16619

Astrobiology, Exoplanet,