Potential Capabilities of Life Itself Extending the Inhabitability Duration of certain Venus-like Exoplanets
Complex existence on Earth is largely believed to be feasible due to Earth's geophysics, particularly its plate tectonics. This allows for substantial amounts of carbon dioxide to be continually eliminated from Earth's atmosphere and reintegrated into its crust.
On the other hand, Venus-like planets at the inner edge of extrasolar habitable zones often exhibit what's known as "stagnant lid" geophysics. This means there's no systematic recycling of the planet's atmosphere, resulting in an early onset of a catastrophic greenhouse effect.
However, a paper set for publication in the journal Astronomy & Astrophysics proposes that planets at the inner edge of a solar system's habitable zone might remain habitable for approximately 2 billion years longer than initially thought. This supposition is based on the assumption that life had developed early enough to prevent a greenhouse effect.
In such a scenario, planets that were previously deemed unsuitable for complex life development might become viable for intelligence evolution.
Researchers propose a novel strategy for identifying life on exoplanets: by searching for lower CO2 levels in atmospheres where higher concentrations are expected. According to Dennis Höning, a planetary scientist at Germany's Potsdam-Institute for Climate Impact Research and the paper's lead author, "Life could counteract rising temperatures by enhancing weather, removing CO2, and extending habitability for billions of years."
The Role of Time
In their research, the team compared the runaway greenhouse onset time between identical planet compositions with and without a biosphere. They found that a biosphere-possessing planet remained habitable for 1-2 billion years longer than an aimless planet, said Höning.
This study marks the first direct link between the CO2 atmospheric signature of planets near the inner edge of the habitable zone and the presence or absence of a biosphere, said Höning and colleagues. They found that planets with low atmospheric CO2 levels in this region are more likely to be inhabited, as biological processes efficiently manage CO2 levels through enhanced weathering, thereby delaying the greenhouse effect and the subsequent dramatic rise in atmospheric CO2.
Biology and Climate Regulation
The researchers propose the idea that low atmospheric CO2 levels on planets near their stars might function as an indirect biomarker. On Earth, the biosphere assists in climate regulation by considerably increasing weathering, which eventually binds CO2 in rocks, acting against the planet's heating, said Höning. They found that life could delay the greenhouse effect by up to 1-2 billion years compared to lifeless planets, said Höning.
Complex Evolution
Extended habitable periods offer life more time to evolve complexity, said Höning. Developing complex or even intelligent life is not a linear process; this extended timeframe could boost the likelihood of a planet developing intelligent life, said Höning.
To locate such planets, Höning suggests searching for rocky planets at least 4 billion years old and examining the aging indicators in their host stars. Subsequently, evaluate the planet's location within its star's habitable zone, said Höning. As the star ages, the habitable zone shifts outward, causing the planet to receive marginally too much energy, causing its water oceans (if they ever existed) to evaporate, said Höning.
The Key Takeaway
This study asserts that a biosphere can counteract a stagnant lid and extend the habitable period, according to Stephen Kane, a planetary geophysicist at the University of California, Riverside, who did not contribute to the study. This research underscores the intricate interplay between a biosphere and its environment, said Kane.
For future telescopes, context is crucial.
Detecting individual molecules is insufficient, said Carone. Methane, a potential biomarker, can be blocked by thick clouds or eliminated through excessive humidity, she said. Ultimately, we might require a multi-telescope strategy to correctly identify habitable exoplanets, said Carone.
The Complexity of Rocky Planets
The intriguing aspect of rocky planets is their complexity, which demands multidisciplinary approaches, said Höning. Integrating geophysics, atmospheric science, astronomy, and even biology is a challenging task, but it's the key to unlocking the next advancements in discovering extraterrestrial life, said Höning.
Venus-like planets at the inner edge of other star systems' habitable zones, which often exhibit "stagnant lid" geophysics, might not be as unsuitable for complex life development as previously thought. This is due to the proposed idea that life could extend the habitability period by managing CO2 levels through enhanced weathering, potentially delaying the greenhouse effect for billions of years.
The researchers suggest that low atmospheric CO2 levels on planets near their stars could function as an indirect biomarker of potential life. This is based on Earth's biosphere's ability to assist in climate regulation by increasing weathering, which eventually binds CO2 in rocks, counteracting the planet's heating and delaying the greenhouse effect.
