Assessing the Feasibility of High-Contrast Direct Imaging in Near-Infrared and Low-Spectra-Resolution Mode with Extremely Large Telescope for Atmosphere of Rocky Exoplanets

In the upcoming decades, one of the primary objectives is to search for habitable planets and signs of extraterrestrial life in the universe. Chemical imbalances in the atmospheres of terrestrial planets can indicate the presence of life. An example of such a biosignature is the thermal-dynamical or photochemical disequilibrium between O₂ and CH₄, as observed in the atmosphere of Modern Earth (beginning 540 million years ago). High-contrast direct imaging with the Extremely Large Telescope (ELT) is a promising method to detect these biosignatures in exoplanets. Habitable planets with reasonable angular separations and contrast can be suitable candidates for direct imaging. In this study, we identified 14 rocky planets and used a framework to simulate the ELT direct imaging of these planets in the near-infrared spectroscopy (NIRS) mode. We quantified the signal-to-noise ratio (SNR) for the detection of CH₄, O₂, H₂O, and CO₂ based on simulated data and ranked the biosignature detectabilities. Our results indicate that GJ 887 b is the most promising candidate for biosignature detection. We also studied the TRAPPIST-1 system, the archetype of nearby transit rocky planet system. We compared the biosignature detection ability of JWST using the transit method and ELT using the direct imaging method. Our findings indicate that JWST is more suitable for detecting and characterizing the atmosphere of small-angular-separation planets.