Liquid water is often touted as the key to finding life on other planets. But what about finding alien technology?
For that, claim two astronomers, the key ingredient might be oxygen.
In a study published in Nature Astronomy, they suggest oxygen in the atmosphere – a mark of the ability for a civilisation to burn things – is the crucial element to developing technology on any planet.
They’re calling it an “oxygen bottleneck”.
“In our paper, we explore whether any atmospheric composition would be compatible with the presence of advanced technology,” says Associate Professor Amedeo Balbi from the University of Roma Tor Vergata, Italy.
“We found that the atmospheric requirements may be quite stringent.”
Balbi and his collaborator, Professor Adam Frank of the University of Rochester, US, argue that fire – combustion – is critical to the development of advanced technology.
“On Earth, fire certainly played a crucial role in the establishment of human civilisation and the onset of technology,” they write.
Fire facilitates cooking, environmental controls and energy, according to the researchers. Of particular importance is metallurgy: extracting, alloying and moulding metals.
“You might be able to get biology – you might even be able to get intelligent creatures – in a world that doesn’t have oxygen,” says Frank, “but without a ready source of fire, you’re never going to develop higher technology because higher technology requires fuel and melting.”
If oxygen makes up less than 16% of the atmosphere, it’s not in a high enough concentration to allow combustion. Below 18.5%, and ignition is very unlikely. Above about 25%, however, and fires become too easy to ignite, leading to widespread combustion and a drop in oxygen levels.
Currently, Earth’s atmosphere is about 21% oxygen, although this has fluctuated over time.
Balbi and Frank found, based on Earth’s history, that control of fire was only possible when oxygen levels were above 18%.
This is their proposed bottleneck: lower than 18% oxygen, and a planet shouldn’t be able to host advanced technology.
“Targeting planets with high oxygen levels should be prioritised because the presence or absence of high oxygen levels in exoplanet atmospheres could be a major clue in finding potential technosignatures,” Frank says.
“The implications of discovering intelligent, technological life on another planet would be huge,” adds Balbi.
“Therefore, we need to be extremely cautious in interpreting possible detections. Our study suggests that we should be sceptical of potential technosignatures from a planet with insufficient atmospheric oxygen.”