Liquid water on exoplanets can be found using new approach

Scientists have introduced a novel approach to discern habitable and potentially inhabited planets by analyzing the carbon dioxide levels in their atmospheres in comparison to neighboring planets.

An international team of researchers, including members from the University of Birmingham (UK) and the Massachusetts Institute of Technology (MIT) (US), has demonstrated that a planet exhibiting lower levels of CO2 in its atmosphere compared to nearby planets indicates the presence of liquid water on its surface. The decline in CO2 levels suggests that the carbon dioxide in the planet’s atmosphere is either dissolving into an ocean or being sequestered by a planetary-scale biomass.

The findings of this research have been published in Nature Astronomy on December 28, 2023.

Habitability, a theoretical concept in astronomy, denotes a celestial body’s ability to host and retain liquid water on its surface. Planets situated too close to their stars are excessively hot (like Venus), while those too distant are exceedingly cold (such as Mars). Planets within the ‘habitable zone,’ often referred to as the Goldilocks zone, are deemed suitable for life.

While significant efforts have been invested in identifying planets within the theoretical habitable zones of their stars, the absence of a method to confirm the presence of liquid water on these planets remained a challenge. Despite progress in defining biosignatures, which are chemical indicators of biological processes, a practical approach for detecting habitability, a crucial indicator of liquid water presence, was lacking.

The researchers devised a new ‘habitability signature’ that enables the identification of planets with liquid water. Previously, scientists had attempted to identify liquid on a planetary surface by observing its glint, the reflection of starlight off water. However, this signature was too faint for current observatories to detect, whereas the new method can be applied with existing facilities.

Amaury Triaud, Professor of Exoplanetology at the University of Birmingham and co-leader of the study, explained, “It is fairly easy to measure the amount of carbon dioxide in a planet’s atmosphere. 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.”

In addition to offering a new method for identifying habitable planets, the research provides insights into environmental tipping points. Triaud notes, “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.”

The innovative method not only serves as a signature for habitability but also functions as a biosignature, given that biology captures carbon dioxide as well.

Ravi Mandalia

Ravi has a masters degree in computer science with specialisation in Network Security and Compliances. He has been at the helm of many news portals and Indian Science is his latest venture.

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