An article published in the journal “Nature Astronomy” reports a study that examines the possibility of using the measurement of carbon scarcity in the atmosphere of a temperate rocky planet as an indicator of the presence of oceans of liquid water and possible life forms. A team of researchers led by Julien de Wit of MIT and Amaury Triaud of the British University of Birmingham devised a strategy based on the James Webb Space Telescope’s detection capabilities and includes an additional step consisting of the detection of ozone.
There are now over 5,000 exoplanets identified and several of them are in their planetary system’s habitable zone. However, that location represents only one of the requirements for the possibility that they host life forms similar to those on Earth. The problem is finding a way to understand whether they are really habitable with liquid water on their surface. This new study offers some ideas for recognizing those cases.
The basic idea came from observing the planets in the solar system’s habitable zone. Earth is the only one of the three on which there’s liquid water and another difference compared to Venus and Mars is the much lower presence of carbon dioxide in its atmosphere.
The researchers assume that the three planets formed similarly, and studies of their history indicate that both Venus and Mars were much more similar to Earth when they were young. Today, their atmospheres contain high percentages of carbon dioxide. On Earth, carbon was largely removed from the atmosphere thanks to a cycle involving the oceans, which absorb this gas.
According to the researchers, rocky exoplanets can be examined for chemical traces of carbon dioxide in their atmospheres. This compound leaves very strong spectral signatures in the infrared, so it’s easy to detect. The presence of more than one rocky exoplanet in a system can help assess where carbon dioxide was absorbed as indirect evidence of liquid water oceans.
Finding a planet habitable for life forms similar to those on Earth offers no certainty that it actually hosts living beings. For this reason, the researchers also proposed the next step in the study of promising exoplanets.
On Earth, photosynthetic organisms absorb carbon dioxide and emit oxygen, which reacts with sunlight to form ozone molecules. This is an easier molecule to detect than the more common one made up of two oxygen atoms. According to researchers, an exoplanet that has little carbon dioxide and at the same time has ozone in its atmosphere is likely to host life forms.
The James Webb Space Telescope was also designed to be able to study the atmospheres of exoplanets. Among other things, it can detect and measure the presence of carbon dioxide and ozone in the atmospheres of rocky exoplanets in systems in the cosmic neighborhood. Where there’s more than one rocky planet, the proposed system works better by comparing the atmospheres of the different planets. The TRAPPIST-1 system, with its seven rocky planets, represents a truly interesting potential target for this type of research.
Finding potentially habitable exoplanets represents one of the frontiers of astronomy. There’s hope that this is another field of research in which the James Webb Space Telescope can lead to great discoveries. In fact, there could be exoplanets inhabited by life forms based on a biochemistry completely different from the Earth’s but for now, it’s only possible to search for biomarkers connected to life forms similar to those on Earth. It’s a field of research where extraordinary progress could come at any time.
