Two researchers said that if you look at the development of technology on Earth, you will find that fire is at the core of it. So what does a fire need to burn? Oxygen, whose chemical signature could provide clues to technological societies in the world beyond our own. So far, researchers have confirmed the existence of more than 5,000 planets beyond Earth. While we don't yet have telescopes powerful enough to show us the surfaces of these exoplanets, we do have astroimagers that can reveal the chemical composition of their atmospheres. Therefore, using this technology is currently our best hope for discovering life on other planets.
To that end, just last week, researchers at MIT and the University of Birmingham proposed studying the carbon dioxide signature of exoplanets. They say those planets with lower carbon dioxide levels are likely worlds filled with huge oceans that have removed carbon dioxide gas from the atmosphere. Where there is alien water, there may be alien life.
Earlier last month, another research team discovered never-before-seen phosphorus in a region of the Milky Way, leading them to believe it could make this a region ripe 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 Rome Tor Vergata in Italy, propose applying another chemical indicator to exoplanets. Searching for levels of oxygen in the atmosphere could help determine not only whether life exists on an exoplanet, but also whether it is advanced enough to develop technology, they say. This is because the presence of oxygen is essential for fire, which they believe is key to creating the components of any advanced technology.
Specifically, they say the oxygen content in an exoplanet's atmosphere would need to exceed 18 percent to facilitate the controlled use of fire -- a number they determined by studying the development of life on our planet.
"In a world without oxygen, you might be able to get living things - you might even get intelligent life - but without a ready source of fire, you'd never be able to develop higher technologies, because higher technologies require fuel and melting," Frank said.
Because life can exist at levels lower than this number, researchers have coined the term "oxygen bottleneck" to describe the critical point in an alien atmosphere required between simply supporting life forms to allowing those life forms to use fire to create advanced technology.
He added: "The presence of high concentrations of oxygen in the atmosphere is like a bottleneck through which you have to pass in order to have a technological species. You can have everything else, but you cannot have a technological species without oxygen in the atmosphere."
Therefore, future searches for planets harboring alien technology should focus only on exoplanets with enough oxygen in their atmospheres, the researchers say. Frank has previously described such indicators as a "technosignal," a measure of an exoplanet's chemical makeup that can indicate whether a society uses advanced technology, whether it's rudimentary metallurgy or the manufacture of microchips.
Balbi said: "The implications of discovering intelligent and technological life on another planet would be enormous. Therefore, we need to be very cautious when interpreting possible detection results. Our study shows that we should be skeptical of potential technological signals from planets with insufficient oxygen in their atmospheres."
Balbi and Frank's research was published in the journal Nature Astronomy.