What are the chances that we’ll hear from an alien civilization someday?
We have no way to estimate how many civilizations might develop the technology for interstellar communication. But University of Rome astronomer Amedeo Balbi and University of Rochester astrophysicist Adam Frank suggest that we could start by figuring out how many planets have atmospheres with enough oxygen to start a fire. They published their work in a recent preprint paper (which has not yet been peer-reviewed).
Most of the time, the search for extraterrestrial intelligence (SETI) means looking for pretty high-tech things: radio signals, giant gleaming cityscapes, interstellar probes, or Dyson spheres. However, building those things requires the ability to work metal, make rocket engines work, and do lots of sophisticated manufacturing. And since all of those things require combustion, you can’t do any of them unless your planet’s atmosphere is at least 16 percent oxygen, and you’re better off with at least 18.5 percent.
In other words, say Balbi and Frank, astronomers looking for signs of high-tech alien civilizations should focus their efforts on planets with oxygen-rich atmospheres.
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