# There's more to life than O$_2$: Simulating the detectability of a range of molecules for ground-based high-resolution spectroscopy of transiting terrestrial exoplanets

**Authors:** Miles H. Currie, Victoria S. Meadows, Kaitlin C. Rasmussen  
**arXiv:** [2304.10683](https://arxiv.org/abs/2304.10683)  
**Date:** 2023-04-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2304.10683v1/

## Key points

- Exoplanet research has focused on finding life beyond our solar system
- Detection of biosignatures, such as atmospheric oxygen (O$_2$), is a promising avenue for finding Earth-like planets orbiting M dwarf stars
- O$_2$ alone does not necessarily indicate the presence of life, additional molecules are needed to provide context and rule out false positives
- Simulations were used to explore the detectability of a range of molecules for ground-based high-resolution spectroscopy of transiting terrestrial exoplanets using extremely large ground-based telescopes (ELTs)
- CH$_4$, CO$_2$, O$_2$, NIR and H$_2$O 0.9 $\mu m $ bands are the most accessible molecules for terrestrial planets transiting a range of M dwarf hosts using an E-ELT, TMT or GMT sized telescope
- ELTs have the potential to reveal two biosignature pairs and detect the molecules necessary to discriminate biological and false positive origins for O$_2$
- Some molecules such as N$_2$ may not be detectable with ELTs
- Continued development of techniques for telluric line subtraction and closer transit targets is needed to fully realize the potential of ELT observations in detecting biosignatures on exoplanets

## Summary

The search for life beyond our solar system has been a major focus of exoplanet research in recent years. One promising avenue is the detection of biosignatures, such as atmospheric oxygen (O$_2$), on Earth-like planets orbiting M dwarf stars. However, the presence of O$_2$ alone does not necessarily indicate the presence of life, as it can also be generated abiotically. Therefore, additional molecules are needed to provide context and rule out false positives. In this study, the authors use simulations to explore the detectability of a range of molecules for ground-based high-resolution spectroscopy of transiting terrestrial exoplanets using extremely large ground-based telescopes (ELTs). They consider pre-industrial and Archean Earth-like atmospheres, as well as lifeless worlds with abiotic O$_2$ buildup from CO$_2$ and H$_2$O photolysis. The simulations include explicit treatment of systematic and telluric effects to model high-resolution spectra for GMT, TMT, and E-ELT configurations for systems 5 and 12 pc from Earth. The results suggest that CH$_4$, CO$_2$, O$_2$, NIR and H$_2$O 0.9 $\mu m $ bands are the most accessible molecules for terrestrial planets transiting a range of M dwarf hosts using an E-ELT, TMT or GMT sized telescope. These molecules can help indicate planetary habitability or reveal alternative biosignatures that could rule out abiotically generated O$_2$. The ELTs have the potential to reveal two biosignature pairs and detect the molecules necessary to discriminate biological and false positive origins for O$_2$. However, some molecules such as N$_2$, which is abundant in Earth's atmosphere but not indicative of life itself, may not be detectable with the ELTs. Although this technique still faces considerable challenges, the ELTs will provide access to the atmospheres of terrestrial planets transiting earlier type M dwarf hosts that may not be possible using JWST. The authors emphasize the need for continued development of techniques for telluric line subtraction and closer transit targets to fully realize the potential of ELT observations in detecting biosignatures on exoplanets.