NASA suggests looking for signs of life on polluted planets
The study examines the presence of gaseous nitrogen dioxide (NO2), which is produced on Earth by the burning of fossil fuels and by volcanic activity.
Ravi Copparapu of NASA's Goddard Space Flight Center in Greenbelt notes that industrial NO2 predominates in the lower atmosphere at altitudes between 10 and 15 km. Hence, he said, the presence of NO2 on another planet could potentially indicate the presence of an industrial civilization.
To date, astronomers have discovered over 4,000 planets orbiting other stars. Some of them may have conditions suitable for life. Since exoplanets are far from Earth, scientists must use powerful telescopes to study their atmospheres.
Previously, the presence of oxygen and methane in the atmosphere was considered as a possible sign on the planet. Now scientists propose to detect the presence of NO2 as well.
Other studies have examined chlorofluorocarbons as possible techno signatures. They were widely used on our planet until it was discovered that it depletes the ozone layer. CFCs are a potent greenhouse gas that is not produced by biological sources. However, they are very specific chemicals that may not be found on other planets, but NO2 is a byproduct of any combustion process.
The research team used computer simulations to predict whether NO2 contamination would be detected using existing and planned telescopes. It turned out that NO2 in our atmosphere actively absorbs some wavelengths of visible light. This confirms that extraterrestrial civilization can be detected at a distance of up to 30 light-years with approximately 400 hours of observation.
Colder than the Sun, stars will produce a stronger and more easily detectable NO2 signal, as they emit less UV light.
However, the difficulty lies in the fact that when NO2 is detected, scientists will have to confirm that it is of industrial origin. So, on Earth, about 76% of NO2 emissions are from industrial activities. To estimate the ratio of natural gas to industrial gas on another planet, you will need to run simulations. In this case, there is a likelihood of a false triggering of the model.
Clouds or aerosol gases in the atmosphere can also interfere with observations. They absorb light with the same wavelength as nitrogen dioxide, so they can mimic its signature. In order to distinguish the presence of NO2 from other gases and clouds, scientists will need to develop advanced 3D models.
In January, a NASA mission led by the Massachusetts Institute of Technology discovered a multi-planetary system. These are four exoplanets orbiting a sun-like star just over 200 light-years from Earth. Scientists plan to observe the system to understand how new planets appear and evolve.