Diagnostic potential of the mid-infrared space interferometer LIFE for studying Earth analogs

With current instruments, it is hard to detect and characterize planets that are similar to the Earth in the habitable zone around their stars. That is why concepts for future space missions have been proposed, from a large IR/O/UV single-aperture telescope for studies in reflected light [1,2], to the Large Interferometer for Exoplanets (LIFE) to characterize the thermal emission of the planetary spectrum [see Quanz+, this conference]. Using nulling interferometry, LIFE will allow us to gather information about the atmospheric structure and composition of a few dozens of terrestrial planets. Because of the lack of observational data, we rely on theoretical spectra of terrestrial exoplanets to develop analysis pipelines that could be most effective for the characterisation of such targets. We feed these spectra to Bayesian retrieval routines to produce a statistically robust analysis of an atmospheric spectrum given a set of parameters (pressure-temperature structure, chemical abundance, planetary dimensions). We have built our own retrieval framework and in an accompanying project we have validated our routines with an Earth twin orbiting a Sun-like star at 10 pc distance from the observer [see Konrad+, this conference]. In this contribution, we analyse simulated spectra of the Earth at various stages of its evolution [3]: a prebiotic Earth at 3.9 billion years ago (Ga), the Earth during the Great Oxygenation Event at 2.0 Ga, and the Neoproterozoic Oxygenation Event at 0.8 Ga, and the modern Earth. We assume to detect such atmospheres on a terrestrial exoplanet at 10 pc distance. This allows us to study the robustness of the framework when branching out of the modern Earth scenario while still in the realm of habitable (and inhabited) exoplanets. We create mock observations with LIFE by running the simulated spectra through the LIFEsim simulator [Ottiger+, subm.], considering all major astrophysical noise sources. We assume a spectral resolution of 50, a signal to noise ratio of 10 at 11 micron, and a wavelength range of 4-18.5 micron, which are the minimum requirements for LIFE [see Konrad+, this conference]. We find that these requirements allow for the identification of the main spectral features of all input spectra (most notably CO₂, H₂O, O₃, CH₄). For the most promising candidates, doubling the S/N would allow us to detect more precise and accurate results of the potential biosignature pair O₃/CH₄ in the biotic epochs.

References:

[1] Gaudi, B. S., et al. (2020), arXiv:2001.06683

[2] Peterson, B. M. et al. (2017), AAS Meeting 229 Abstracts, 405.04

[3] Rugheimer S. & Kaltenegger L. (2018), ApJ, 854 19