Till date, oxygen has been thought to be essential for life. Now, a Japanese researcher has presented a novel hypothesis that it could be possible for distant planets to have large quantities of abiotic (non-biologically produced) oxygen.
According to assistant professor Norio Narita from the Astrobiology Center of National Institutes of Natural Sciences (NINS), abiotic oxygen produced by the photocatalytic reaction of titanium oxide and known to be abundant on distant planets and the moon cannot be discounted.
"To search for life on extrasolar planets through astronomical observation, we need to combine the knowledge from various scientific fields and to promote astrobiology researches to establish the decisive signs of life," Narita noted.
"Although oxygen is still one of possible biomarkers, it becomes necessary to look for new biomarkers besides oxygen from the present result," he added.
The Earth's atmosphere contains oxygen because plants continuously produce it through photosynthesis.
For a planet with an environment similar to the Sun-Earth system, continuous photocatalytic reaction of titanium oxide on about 0.05 percent of the planetary surface could produce the amount of oxygen found in the current Earth's atmosphere.
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In addition, the team estimated the amount of possible oxygen production for habitable planets around other types of host stars with various masses and temperatures.
They found that even in the least efficient production case of a low-temperature star, the photocatalytic reaction of the titanium oxide on about 3 percent of the planetary surface could maintain this level of atmospheric oxygen through abiotic processes.
"In other words, it is possible that a habitable extrasolar planet could maintain an atmosphere with Earth-like oxygen, even without organisms to perform photosynthesis," the authors noted.
This study is a good example of inter-disciplinary studies that combine knowledge from different fields of science to promote astrobiology in the search for life on extrasolar planets.
The paper appeared in the journal Scientific Reports.