Astronomers Investigate CO as a Potential Biosignature on Exoplanets

A new study titled “Relative abundances of CO2, CO, and CH4 in atmospheres of Earth-like lifeless planets” examines the presence of carbon species, particularly carbon monoxide (CO), in the atmospheres of exoplanets that are similar to Earth. The aim of the study is to understand how the presence of CO can potentially indicate the existence of simple life on these exoplanets.

Carbon, in this context, refers to major carbon species such as carbon dioxide (CO2), carbon monoxide (CO), and methane (CH4). The research focuses on determining the conditions under which a CO-rich atmosphere could form, as this could be favorable for the origin of life. The authors of the study, Yasuto Watanabe and Kazumi Ozaki, affiliated with the University of Tokyo and the Tokyo Institute of Technology, respectively, aim to unravel the complexities of exoplanet atmospheres in order to identify specific carbon molecule mixtures that could serve as biosignatures.

The study explores a concept called CO runaway, which occurs in atmospheres similar to early Earth’s atmosphere that had limited amounts of oxygen. CO is produced through photodissociation from UV radiation and is destroyed by chemical reactions resulting from the photodissociation of water. However, under certain conditions, more CO can be produced than destroyed, leading to CO runaway. This phenomenon is significant because a CO-rich atmosphere is more conducive to the creation of prebiotic chemicals necessary for life compared to a CO2-rich atmosphere.

Using atmospheric chemistry models, the researchers discovered a distinct gap structure in atmospheric chemistry that could be vital for the presence of life. The results suggest that an observable gap exists in the phase space of pCH4/pCO2 versus pCO/pCO2, indicating the potential presence of a CO gap. This gap structure, resulting from the different behaviors of atmospheric CO and CH4, could be a common feature among various Earth-like exoplanets.

In conclusion, understanding the relative abundances of carbon species in exoplanet atmospheres has significant implications for the search for habitable planets beyond our solar system. The study’s findings shed light on how the presence of CO in an exoplanet’s atmosphere could serve as a potential biosignature, indicating the possibility of simple life forms existing on these distant worlds.

Sources:
– “Relative abundances of CO2, CO, and CH4 in atmospheres of Earth-like lifeless planets” – Yasuto Watanabe and Kazumi Ozaki (pre-print on arXiv)
– Image source: Watanabe and Ozaki 2023