CO2 Levels Hold Key to Finding Habitable Planets

Thursday - January 4 2024, 01:16 UTC - 10 months ago

Scientists have devised a new way to identify habitable planets based on the amount of carbon dioxide in the atmosphere, by comparing it with neighboring planets. The method requires current facilities using infrared light to observe, and helps show environmental tipping points. The lead author of the research is Amaury Triaud, Professor of Exoplanetology at the University of Birmingham.

Atmospheric CO2 levels hold the key to finding habitable planets and potentially life itself.

Scientists have devised a new way to identify habitable planets and potentially inhabited planets, by comparing the amount of carbon dioxide in their atmosphere, to neighboring planets. An international team of researchers from the University of Birmingham (UK), the Massachusetts Institute of Technology (MIT) (US), and elsewhere, have shown that if a planet has a reduced amount of CO2 in its atmosphere compared to neighboring planets, it suggests there is liquid water on that planet’s surface. The drop in CO2 levels implies that the carbon dioxide in the atmosphere of the planet is being dissolved into an ocean or sequestrated by a planetary-scale biomass.

The research was published on December 28, 2023, in Nature Astronomy.

Habitability is a theoretical astronomical concept that means that a celestial body is capable of hosting and retaining liquid water on its surface. Planets too close to their star are too hot (such as Venus), those too far, are too cold (like Mars), whereas planets in the ‘habitable zone’ are just right. The habitable zone is sometimes referred to as the Goldilocks zone.

The researchers devised a new ‘habitability signature’ with which they can identify whether a planet does indeed have liquid water. Before this, the closest scientists had come to identifying liquid on a planetary surface was to use its glint, how starlight reflects off water. However, this signature is far too weak for current observatories to detect whereas the new method can be applied with current facilities.

Amaury Triaud, Professor of Exoplanetology at the University of Birmingham, who co-led the study said: “It is fairly easy to measure the amount of carbon dioxide in a planet’s atmosphere. This is because CO2 is a strong absorber in the infrared, the same property causing the current rise in global temperatures here on Earth. By comparing the amount of CO2 in different planets’ atmospheres, we can use this new habitability signature to identify those planets with oceans, which make them more likely to be able to support life.

“For example, we know that initially, the Earth’s atmosphere used to be mostly CO2, but then the carbon dissolved into the ocean and made the planet able to support life for the last four billion years or so.” .

As well as developing a new way to identify habitable planets, the research can be used to reveal more insights into environmental tipping points.

Amaury Triaud continues, “By examining the levels of CO2 in other planets’ atmospheres we can empirically measure habitability and compare it to our theoretical expectations. This helps gather context for the climate crisis we face on Earth to find out at which point the levels of carbon make a planet uninhabitable. For example, Venus and Earth look incredibly similar, but there is a very high level of carbon in Venus’ atmosphere. There may have been a past climatic tipping point that led to Venus becoming uninhabitable.” .