The conditions favouring the rise of advanced aliens are much rarer than previously thought, according to a new study, which suggests the nearest planet hosting extraterrestrial civilisation could be 33,000 light years away.
For such technologically advanced aliens to exist at the same time as us, their civilisation would have to be at least 280,000 years old, according to research recently presented at the joint meeting of the Europlanet Science Congress and the American Astronomical Society’s Division for Planetary Science (EPSC-DPS2025).
Researchers from the Austrian Academy of Sciences arrived at these numbers by considering the odds of finding Earth-like worlds that have plate tectonics, and a nitrogen-oxygen-dominated atmosphere with just the right amount of oxygen and carbon dioxide.
These factors make the possibility of the success of finding extraterrestrial intelligence “bleak”, they say.
“Extraterrestrial intelligences – ETIs – in our galaxy are probably pretty rare,” Manuel Scherf from the Space Research Institute said.
Scientists drew parallels to the evolution of life on Earth, observing that our planet’s atmosphere is dominated by nitrogen (78 per cent) and oxygen (21 per cent), as well as trace gases like carbon dioxide (0.042 per cent).
The research argues that the more carbon dioxide a planet has in its atmosphere, the longer it can sustain conditions conducive for life, and prevent its atmosphere from escaping into space.
However, they observe that such a planet would need a careful balance, as too much carbon dioxide can lead to a runaway greenhouse effect or render the atmosphere too toxic for life.
A planet with higher levels of carbon dioxide, like ten per cent of the gas, could avoid a runaway greenhouse if it is further from its sun, or its sun is younger.
Researchers estimate that such a planet could at best maintain conditions conducive to life for 4.2 billion years.
On the other hand, a planet whose atmosphere has about 1 per cent carbon dioxide can maintain a biosphere for a maximum of 3.1 billion years, they say.
In both these cases, the worlds would also need no less than 18 per cent oxygen, scientists say.
If oxygen levels fall below this threshold, conditions won’t enable combustion and fire, without which smelting of metal would be unfeasible and negate any possibility for the rise of a technological civilisation, they say.
Plate tectonics also plays a role in regulating the amount of carbon dioxide in the atmosphere via the carbon-silicate cycle, meaning any habitable planet would require this geological process.
But despite these processes, any planet, including the Earth, faces the risk of the carbon dioxide gradually being drawn out of the atmosphere and getting locked away in rocks, rather than being recycled.
“At some point, enough carbon dioxide will be drawn from the atmosphere so that photosynthesis will stop working...For the Earth, that’s expected to happen in about 200 million to roughly one billion years,” Dr Scherf said.
Comparing these lifespans with the amount of time it takes for technological life to evolve, scientists estimated the possible lifetime of a technological species, which on Earth rose after 4.5 billion years.
With these factors in mind, researchers concluded that technological species living on a planet with 10 per cent carbon dioxide would have to survive for at least 280,000 years for there to even be one other civilisation in the galaxy at the same time we are.
“The numbers of ETIs are pretty low and depend strongly upon the lifetime of a civilisation,” Dr Scherf said.
The findings suggest that if we do detect an ETI, it is most likely to be much older than humanity.
Based on these calculations, scientists estimate that the next closest technological civilisation is 33,000 light years away, which is about the distance to the other side of the Milky Way.
“Although ETIs might be rare there is only one way to really find out and that is by searching for it,” Dr Scherf says.
“If these searches find nothing, it makes our theory more likely, and if SETI does find something, then it will be one of the biggest scientific breakthroughs ever achieved as we would know that we are not alone in the Universe,” he added.
New black hole discovery changes what we know about cosmic evolution
NASA will say goodbye to the International Space Station in 2030. Here’s why
NASA launches new satellites to uncover secrets of the sun
Astronomers want to blow up this asteroid before it may strike Moon
SpaceX completes final test ahead of crucial Starship launch
Nasa’s Moon mission could be ‘years late’ due to issues with Elon Musk’s Starship
