![]() ![]() They also looked at the scenario of an exoplanet that is an analog of the early-Earth, where life existed but where there was still very little oxygen in the atmosphere. Carbon dioxide seasonality would be difficult to detect on other planets, but it is a powerful indicator of the presence of life since it is unlikely to occur on planets with an ocean unless life is present. This is seen on Earth, where the ocean-dominated Southern Hemisphere has a weaker CO 2 variability signal than the Northern Hemisphere. They found that the seasonal carbon dioxide (CO 2) signal would be dominated by land-based ecosystems, which are in direct contact with the atmosphere, indicating that CO2variability might not be detectable on ocean worlds. Carbon dioxide is an important atmospheric component on habitable worlds due to the role it plays in climate regulation via weathering. The researchers examined the seasonal variations in carbon dioxide on Earth, a signal that could be detectable on other planets assuming that life elsewhere is also carbon-based. ![]() The maximum production of oxygen occurs during the summer months when temperatures are warm. Photosynthesis occurs as carbon dioxide and water react to become organic matter and oxygen, and aerobic respiration causes the reverse reaction, producing carbon dioxide and water. Seasonal variations shift the balance between two different reactions: photosynthesis and aerobic respiration. Seasonality in the Earth’s atmosphere arises because of the interactions between the biosphere and the varying solar radiation reaching Earth at different points in its orbit. “Rather that simply recognizing that a planet hosts life, we may be able to say something about how the activities of its biosphere vary in space and time,” says Olson. By understanding how atmospheric gases vary over the course of a year on Earth, it will help inform scientists about what signals to look for on other planets. Signals from an exoplanet that vary over time, such as with the seasons, could help to rule out false positives or negatives that occur in single snapshot observations. The second paper is by Joshua Krissansen-Tottonat the University of Washington, along with Olson and David Catling, and looked at potential biosignatures produced by atmospheric gases that can only co-exist in the presence of life. Now, two recent papers discuss new ways of looking for biosignatures by studying how life can influence a planet’s atmosphere.Ī paper by Stephanie Olson at the University of California, Riverside, and colleagues, discusses how seasonal changes in the atmosphere caused by life could be used as a biosignature. Similarly, methane is produced by life and is a potential biomarker, but can also be produced by other means. Oxygen is produced by photosynthesis and is commonly thought to be a potential biosignature on other worlds, although it is also possible for oxygen to be produced from abiotic sources. ![]()
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