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Study Indicates That Possible Alien Civilizations in the Milky Way Would Be 33 Light-Years Away and Up to 280,000 Years Older
A study presented at the Europlanet Scientific Congress – Joint Meeting of the Division of Planetary Sciences 2025 (EPSC–DPS 2025) proposes that, if alien civilizations exist in the Milky Way, they are likely rare, extremely distant, and much older than humanity.
The authors suggest that the nearest technological civilization may be about 33,000 light-years from Earth and have about 280,000 years of evolutionary advantage.
According to the researchers, the chance of two technological species coexisting at the same time is minimal.
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This time interval drastically reduces the likelihood of communication or mutual detection between alien civilizations and the human species, limiting the potential for interstellar interactions even on astronomical scales of time and space.
Atmosphere and Tectonics as Prerequisites for Complex Life
The research highlights that the existence of alien civilizations depends on a specific combination of environmental factors.
Among the essential elements identified are the appropriate atmospheric composition and the presence of ongoing geological activity, both considered determinants for the emergence and maintenance of complex organisms and, subsequently, technologically advanced societies.
On Earth, the atmosphere is primarily composed of nitrogen (78%) and oxygen (21%), with a very small but crucial fraction of carbon dioxide (0.042%). This balance allows photosynthesis and sustains the biosphere.
According to the study, significant variations in this balance would make complex biological processes impossible on other worlds.
Risk of Biosphere Collapse Without Gas Balance
The authors note that the absence or excess of carbon dioxide drastically alters the stability of ecosystems.
Very low concentrations would cause the collapse of the biosphere, as plants would not be able to perform photosynthesis.
In contrast, elevated levels could induce an uncontrolled greenhouse effect or generate widespread atmospheric toxicity, preventing the emergence of complex and lasting forms of life.
The maintenance of this balance depends on plate tectonics, which regulates the amount of atmospheric carbon dioxide through the carbon-silicate cycle.
This process removes gas from the atmosphere and gradually returns it over geological time.
However, scientists warn that excessive carbon accumulation in rocks could halt photosynthesis, eliminating essential support for life.
Scarcity of Extraterrestrial Intelligences in the Milky Way
The study concludes that the combination of necessary conditions for the evolution of alien civilizations makes their occurrence extremely rare.
The difficulty in achieving a stable atmosphere, constant geological activity, and sufficient evolutionary time drastically reduces the number of habitable planets capable of generating advanced technological species.
According to researcher Manuel Scherf from the Space Research Institute of the Austrian Academy of Sciences, “extraterrestrial intelligences — ETIs — in our galaxy are likely very rare.”
This statement reflects the estimate that the probability of such civilizations coexisting with humanity in the same time frame is extremely low.
Implications for the Search for Extraterrestrial Intelligence
While the study reinforces the hypothesis of the scarcity of alien civilizations, the authors advocate for the continuation of the search for extraterrestrial intelligence (SETI). According to Scherf, only direct investigation can confirm or refute the proposed model.
If the searches remain fruitless, the scenario of cosmic isolation will become more plausible.
If SETI identifies signals from another civilization, it would represent one of the greatest scientific advances in history, demonstrating that humanity is not alone in the universe.
The study also emphasizes that the current balance of Earth’s atmosphere is delicate and temporary.
Therefore, substantial changes in this system could compromise the stability required for the maintenance of complex life on the planet, reinforcing the uniqueness and vulnerability of the conditions that sustain human civilization.
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