Nearest Alien Civilization Could Be 33,000 Light-Years Away, Study Suggests

At a joint meeting of the European Planetary Science Congress (EPSC) and the Division for Planetary Sciences (DPS) in Helsinki, scientists from the Space Research Institute of the Austrian Academy of Sciences unveiled a new study suggesting that the nearest technological civilization in our galaxy could be as far as 33,000 light-years away.

According to their findings, for such a civilization to exist at the same time as humanity, it would need to endure for at least 280,000 years, and possibly for millions of years.

The researchers found that planets combining both plate tectonics and a nitrogen-oxygen atmosphere—conditions considered vital for life—are exceedingly rare. These harsh planetary requirements cast doubt on the likelihood of detecting extraterrestrial civilizations anytime soon.

The study emphasizes the pivotal role of carbon dioxide in sustaining life: in the right amounts, it supports photosynthesis and stabilizes the atmosphere, but excessive levels can trigger runaway greenhouse effects or atmospheric toxicity. Plate tectonics help regulate CO₂ through the carbon-silicate cycle. Over geological timescales, however, CO₂ eventually becomes locked into rocks, halting photosynthesis. For Earth, this process is expected to unfold within 200 million to 1 billion years.

Model simulations show that a planet with 10% CO₂ could sustain a biosphere for up to 4.2 billion years, while one with 1% CO₂ would remain habitable for only 3.1 billion years. Moreover, advanced life requires an atmospheric oxygen level of at least 18%—the minimum needed for open-air combustion, metal smelting, and the development of technology.

By comparing the lifespan of habitable environments with the time it took for intelligent life to evolve on Earth, the study concludes that a technological civilization would need to last at least 280,000 years to coexist with us in the Milky Way. If ten civilizations were to coexist, each would need an average lifespan exceeding 10 million years.

These calculations suggest that any neighboring intelligent civilization could be situated on the far side of the Milky Way, some 33,000 light-years away. The researchers caution, however, that key factors such as the probability of life's origin, the emergence of photosynthesis, and the evolution of multicellular organisms remain unknown, leaving significant uncertainty in the final estimates.