Detecting aliens through CO2: New method may spot life on distant planets
Essentially, the approach involves comparing the amount of carbon dioxide on the subject planet with that on neighboring planets and assessing the ozone concentration. Notably, such studies are feasible in today's context.
Planets with potential water and life
The research team made up of scientists from the University of Birmingham and the Massachusetts Institute of Technology posits that a planet with significantly less carbon dioxide in its atmosphere than neighbouring planets stands a high chance of having water, and possibly life.
A decrease in the CO2 concentration could be an indicator that the gas has been absorbed by oceans or biomass, serving as a crucial pointer in identifying planets that might host life.
Up until now, scientists' predictions of water and life on other planets were primarily based on theoretical analysis. They considered factors like the intensity of the star's radiation, on which the planet depends, and its distance from the star.
If a planet is too close to its star, intense radiation causes evaporation of water. Conversely, when the planet is too distant, water freezes, both scenarios impede or prevent the development of life.
From experimental viewpoints, it was proposed to observe the reflection of starlight from a potential ocean, but the current instruments are inadequate for this observation.
New approach
Meanwhile, the novel method of contrasting the amount of carbon dioxide on different planets is simple to apply and doesn't necessitate specialized equipment.
"Measuring the amount of carbon dioxide in a planet's atmosphere is relatively simple as CO2 strongly absorbs infrared radiation, contributing to global warming on Earth. By contrasting the concentration of CO2 in the atmospheres of different planets, we can gauge the presence of oceans and single out planets more likely to have life," explains Prof. Amaury Triaud of the University of Birmingham, co-author of the report published in the 'Nature Astronomy' magazine.
Looking at carbon dioxide on faraway planets might also hint at life, not just water and hospitable conditions.
"On Earth, living beings store 20% of all absorbed carbon dioxide, while the rest is mainly absorbed in oceans. On other planets, this fraction could be substantially more. A sign of CO2 absorption by living entities is the emission of oxygen, which can subsequently transform into ozone. Just like CO2, ozone can be detected on distant planets. Thus, tracking the concentration of carbon dioxide and ozone can inform us of whether a planet hosts life," explains Prof. Julien de Wit from MIT.
A significant advancement?
"Contrary to the prevalent skepticism, our work elicits new hope that the James Webb Space Telescope (JWST) will detect life on exoplanets. Through this carbon dioxide signature, we can not only infer the presence of liquid water but also identify life forms," emphasizes Prof. de Wit.
Investigating the volume of carbon dioxide on exoplanets can also be informative about Earth itself.
"By quantifying the concentration of CO2 in the atmospheres of other planets, we can empirically check the plausibility of life development and juxtapose the results against our theoretical models. In doing so, we can better understand the ongoing climate crisis on Earth and figure out the CO2 concentration at which a planet becomes uninhabitable. For instance, Venus and Earth appear quite similar, but Venus has a vastly higher carbon dioxide concentration. In its history, there could have been a tipping point that made Venus uninhabitable," elaborates Prof. Triaud.
