The presence of oxygen in a planet's atmosphere is not a definitive sign that aliens are present, a new study has found.

A team of scientists from John Hopkins University simulated the atmospheres of different planets outside of the solar system. They report that they have successfully created both organic compounds and oxygen inside the lab, but no life.

Their findings were published in the journal ACS Earth and Space Chemistry.

Searching Beyond Oxygen-Rich Exoplanets

To create a simulation of a planetary atmosphere, the team used Planetary Haze (or PHAZER) chamber to test nine different gas mixtures that are consistent with predictions for types of exoplanets that are most common within the Milky Way Galaxy. The researchers then exposed these mixtures to temperatures ranging from about 80 to 700 degrees Fahrenheit.

After three days, the research team measured and identified the resulting gasses and found multiple scenarios where oxygen and organic molecules that could build sugars and amino acids.

"Our experiments produced oxygen and organic molecules that could serve as the building blocks of life in the lab, proving that the presence of both doesn't definitively indicate life," stated Chao He, an assistant research scientist and the first author of the study. "Researchers need to more carefully consider how these molecules are produced."

The Oxygen Problem

Oxygen on Earth is abundant. Oxygen makes up 20 percent of the atmosphere and is considered to be one of the most robust biosignature gases on the planet.

However, the human race can thank plants and cyanobacteria for Earth's oxygen-rich atmosphere. Without biology, there will be no oxygen.

Little is understood about how different energy sources initiate chemical reactions and how chemical reactions can create biosignatures — like oxygen— in other planets. He said that, while similar studies have been conducted in the past, theirs is the first that was conducted in the lab.

A separate study also refuted the axiom that oxygen in the atmosphere is a definitive sign of alien life. The researchers argued that an oxygen-rich atmosphere might have been caused by red dwarfs, which are very common within the Milky Way Galaxy, hot enough to vaporize a nearby planet, with the hydrogen escaping into space. 

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