Atmospheric seasonal changes is a promising bio-signature because it is a sign of life on Earth and is probably to be present on inhabited exoplanets, as well. So says Stephanie Olson, a researcher at the Center for Alternative Astrobiology at the University of California, Riverside, and lead author of a study published in Astrophysical Journal.
As the Earth orbits the Sun, its inclined axis means that different regions receive more sunlight at different times of the year. The most visible signs of this phenomenon are changes in climate and the length of days but the atmospheric composition is also affected.
For example, in the northern hemisphere, which contains most of the world’s vegetation, plant growth in summer produces significantly lower levels of carbon dioxide in the atmosphere. The opposite happens with the oxygen.
“Inferring life on a seasonal basis would not require a detailed understanding of extraterrestrial biochemistry because it arises as a biological response to seasonal changes in the environment, rather than as a consequence of a specific biological activity that may be unique to the Earth,” Olson adds in a statement.
Atmospheric seasonal changes might represent the ideal method of finding inhabited exoplanets
In the study, the researchers identify the opportunities and difficulties associated with the characterization of seasonal formation and the destruction of oxygen, carbon dioxide, methane and their detection by an imaging technique called spectroscopy.
They also modeled the fluctuations of atmospheric seasonal changes in the case of oxygen on an inhabited exoplanet with low oxygen content, such as the Earth used to be several billions of years ago.
They found that ozone (O3), which is produced in the atmosphere through reactions involving oxygen (O2) gas produced by life forms, would be a more easily bio-signature for seasonal oxygen variability than O2 itself on weakly oxygenated planets.
“It’s really important that we accurately model these kinds of scenarios now so that the space and ground-based telescopes of the future can be designed to identify the most promising bio-signature,” explained Edward Schwieterman, a NASA researcher and Ph.D. at UCR. Scientists concluded that the same atmospheric seasonal changes found in Earth’s atmosphere can be applied as a detection method of inhabited exoplanets.