Carbon-Lite Atmosphere May Indicate Water and Life on Other Planets, Researchers Say


A carbon-lite atmosphere could be a potential indication of liquid water and the potential for life on terrestrial planets, according to a study conducted by scientists at MIT, the University of Birmingham, and other institutions. The researchers propose that if a planet has significantly less carbon dioxide in its atmosphere compared to other planets in the same system, it could be indicative of liquid water and the possibility of life on its surface.

The findings of the study, which is set to be published in Nature Astronomy, suggest that the absence of a specific chemical feature in planetary atmospheres could provide astronomers with the best chance of finding liquid water and signs of life on other planets. The researchers claim that this new signature, characterized by relatively depleted carbon dioxide, is the only detectable sign of habitability with current technologies.

While current telescopes can determine a planet’s distance from its star and its orbit time, these measurements do not confirm the presence of liquid water and thus do not provide direct evidence of a planet’s habitability. The team looked at similarities between Venus, Earth, and Mars, noting that Earth is the only planet among the three that currently possesses liquid water and has significantly less carbon dioxide in its atmosphere.

Based on their observations, the team posits that if a planet in a distant system exhibits a depletion of carbon dioxide relative to neighboring planets, this would be a reliable indicator of the presence of liquid water and potentially life on its surface. The Earth’s oceans, and the subsequent absorption of carbon dioxide, have played a crucial role in regulating climate and supporting habitability over billions of years.

The team proposes a strategy to detect habitable planets by searching for a signature of depleted carbon dioxide. This search would be most effective for systems in which multiple terrestrial planets of similar size orbit closely together, much like the planets within our own solar system. The first step would involve confirming the presence of atmospheres on these planets, followed by measuring their carbon dioxide content. Planets that show significantly less carbon dioxide than the others would be considered habitable, potentially indicating the presence of liquid water.

However, habitable conditions on a planet do not necessarily guarantee the presence of life. To determine the likelihood of life, the researchers suggest that astronomers also look for the presence of ozone in a planet’s atmosphere. On Earth, plants and some microbes contribute to removing carbon dioxide from the atmosphere and emit oxygen, which reacts with sunlight to form ozone.

If a planet’s atmosphere exhibits both depleted carbon dioxide and signs of ozone, there is a high probability that the planet is habitable and may support life. The researchers estimate that NASA’s James Webb Space Telescope (JWST) would be capable of measuring carbon dioxide and potentially ozone in nearby multi-planet systems, such as TRAPPIST-1, a seven-planet system located just 40 light years away from Earth.

TRAPPIST-1 is among a handful of systems where terrestrial atmospheric studies could be conducted using the JWST, providing a roadmap for the discovery of habitable planets. The researchers suggest that with collaborative efforts, paradigm-shifting discoveries could be made within the next few years.

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