Look at the development of Earth-bound tech and you'll find fire at the heart of it, says a duo of researchers. And what does fire need to burn? Oxygen, whose chemical signature could provide clues to technological societies on worlds beyond our own.
To date, researchers have already confirmed the existence of more than 5,000 planets beyond Earth. While we don't yet have telescopes that are powerful enough to show us the surface of these exoplanets, we do have celestial imagers that can reveal the chemical composition of their atmospheres. Using that technology, then, is currently our best hope at finding life on other planets.
To that end, just last week researchers from MIT and the University of Birmingham recommended looking at the carbon dioxide signatures of exoplanets. Those with a low level, they said, would likely be worlds filled with vast oceans that had removed the gas from the atmosphere. And where there's alien water, there just might be alien life.
Earlier last month, a different team of researchers spotted phosphorus in an area of the galaxy in which it hadn't been seen before, leading them to believe it could make it a ripe zone for life.
Now Adam Frank, a professor of physics and astronomy at the University of Rochester, and Amedeo Balbi, an associate professor of astronomy and astrophysics at the University of Roma Tor Vergata in Italy propose applying another chemical metric to exoplanets. Searching for a certain level of atmospheric oxygen, they say, will help determine not only if life exists on an exoplanet, but also if it is advanced enough to have developed technology. That's because the presence of oxygen is critical for fire, and fire, they argue, is key to creating the components of any advanced tech.
Specifically, they say the level of oxygen in an exoplanet's atmosphere needs to be over 18% in order to facilitate the controlled use of fire – a figure they determined by examining the advancement of life on our own planet.
“You might be able to get biology – you might even be able to get intelligent creatures – in a world that doesn’t have oxygen, but without a ready source of fire, you’re never going to develop higher technology because higher technology requires fuel and melting,” Frank said.
Because life can exist at levels below this figure, the researchers have coined the term "oxygen bottleneck" to describe the tipping point needed in an alien atmosphere between simply supporting lifeforms and allowing those lifeforms to use fire in the creation of advanced tech.
“The presence of high degrees of oxygen in the atmosphere is like a bottleneck you have to get through in order to have a technological species,” Frank added. “You can have everything else work out, but if you don’t have oxygen in the atmosphere, you’re not going to have a technological species.”
The researchers say that future searches for planets harboring alien technology should therefore be focused only on exoplanets with sufficient oxygen in the atmospheres. Frank had previously described such a metric as a "technosignature," a measure of an exoplanet's chemical makeup that could point to the existence of a society's use of advanced technology, whether that be rudimentary metallurgy or the creation of microchips.
“The implications of discovering intelligent, technological life on another planet would be huge,” said Balbi. “Therefore, we need to be extremely cautious in interpreting possible detections. Our study suggests that we should be skeptical of potential technosignatures from a planet with insufficient atmospheric oxygen.”
Balbi and Frank's work has been published in the journal Nature Astronomy.
Source: University of Rochester