In their search for life in solar systems near and far, researchers have often accepted the presence of oxygen in a planet's atmosphere as the safest sign that life may be present there. However, a new Johns Hopkins study recommends a review of the rule of thumb.
Simulate in the lab's atmosphere of planets in addition to the solar system, scientists successfully created both organic compounds and oxygen, absent in life.
The results, published December 11th in the journal ACS Earth and Space Chemistry, serving as a precautionary story for researchers who suggest the presence of oxygen and organic substances in distant worlds is proof of life there.
"Our experiments produced oxygen and organic molecules that can serve as the building blocks of life in the laboratory, which shows that the presence of both does not definitely show life," said Chao He, assistant researcher at Johns Hopkins University Department of Earth and Planetary Sciences and the first author of the study. "Researchers need to carefully consider how these molecules are produced. "
Acid accounts for 20 percent of the Earth's atmosphere and is considered to be one of the most robust biosignature gases in the earth's atmosphere. However, the search for life beyond the Earth's solar system is a bit known about how different sources of energy initiate chemical reactions and how these reactions can create biosignatures like acid. While other researchers have driven photochemical models on computers to predict what exoplanet environments could create, no such simulations to his knowledge have previously been carried out in the laboratory.
The research team conducted the simulation experiments in a specially designed Planetary HAZE (PHAZER) chamber in the laboratory Sarah Hörst, Assistant Professor of Earth and Planet Sciences, as well as the co-author of the paper. The researchers tested nine different gas mixtures, in accordance with predictions for super-soil and mini-Neptune-type exoplanet atmospheres; Such exoplanets are the most abundant type of planet in our Milky Way galaxy. Each blend had a specific composition of gases, such as carbon dioxide, water, ammonia and methane, and each heated at temperatures ranging from about 80 to 700 degrees Fahrenheit.
He and the team allowed each gas mixture to flow into the PHAZER setting and then expose the mixture to one of two types of energy intended to emulate energy that triggers chemical reactions in planetary atmospheres: plasma from an AC light or light from an ultraviolet lamp. Plasma, a source of energy stronger than UV light, can simulate electrical activities such as lightning and / or energetic particles, and UV light is the main driving force for chemical reactions in planetary atmospheres such as Earth, Saturn and Pluto.
After the experiments were run continuously for three days, corresponding to the amount of time gas, would be exposed to energy sources in space, the researchers were measured and identified the resulting gases with a mass spectrometer, an instrument that sorted chemical substances through their bulk to charge ratio.
The research group found several scenarios that produced both oxygen and organic molecules that could build sugars and amino acids – raw materials for which life could begin – like formaldehyde and hydrogen cyanide.
"People used to suggest that oxygen and organic substances are present together indicate life, but we produced them abiotic in several simulations," he says. "This suggests that even the awareness of widely accepted biosignatures can be a false positive for life."
This study was funded by NASA Exoplanet's Research Program Grant NNX16AB45G. Chao He received funding from Morton K. and Jane Blaustein Foundation.
Johns Hopkins University. .