Astronomers identify trick to root out false-positives in the search for life

Artist's impression of Kepler 62e, an exoplanet in the habitable zone of a small red dwarf in the constellation Libra(Credit: NASA Ames/JPL-Caltech/T. Pyle)

A new study hopes to cut down on false positive readings in the search for ET. It highlights two scenarios in which the detection of oxygen (O2) in the atmosphere of a distant exoplanet would not represent the presence of extraterrestrial life.

One of the methods currently in use by astronomers engaged in the hunt for extraterrestrial life is to analyze the atmospheres of distant exoplanets searching for O2, a gas which on Earth is created largely via photosynthesis in plants and algae, and is synonymous with the existence of life.

So, how do astronomers determine whether an exoplanet has O2 in its atmosphere? Scientists are able to observe exoplanets as they pass in front of their parent stars, taking the opportunity to analyze the spectral features of the light as it glances through the planet's atmosphere. From this, astronomers are able to break down the composition of the atmosphere, and infer certain characteristics about their quarry, including the interpretation of significant levels of O2 as a potential indicator for life.

However, a new study has outlined two cases in which the detection of O2 in the atmosphere of a distant planet would provide a false positive indicator in the search for life. In both scenarios, the O2 present in an exoplanet's atmosphere would exist as a result of abiotical production.

One such scenario would see ultraviolet light from a common star smaller than our Sun strike an exoplanet's atmosphere, breaking down carbon dioxide (CO2) to free O2 particles. The team ran computer models to simulate the interaction and discovered that alongside producing O2, that the CO2 split would also produce large quantities of carbon monoxide (CO)

Therefore, if oxygen is detected alongside a strong presence of CO2 and CO, it could represent a false positive. A low-mass star is once again the catalyst for another potential false positive indicator in the search for life wherein light from the star could work to break down atmospheric water.

This creates vast quantities of O2 which may collide with each other to create short lived O4 molecules. The detection of O2 alongside O4 could serve as another indicator for a false positive, allowing astronomers to save valuable time by viewing more promising targets.

Research such as this will provide a valuable framework in the search for life, as it is aided by the next generation of scientific instruments, including NASA's greatly anticipated James Webb Space Telescope.

A paper on the study has been published in The Astrophysical Journal.

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