The Universe is a big place, so scientists are keen-to narrow down their look for alien life, may be by trying to find radio signals or hospitable climates or huge megastructures. Now other sign of alien life that is under consideration: atmospheric pollution.
If there are alien civilizations out-there, hypothesis goes, then their activities & industries may produce pollution like ours have. That pollution might be something that we could be able to spot in our scans of deep space.
A new study suggests, nitrogen dioxide gas (NO2) could indicate-life on other planets: It can be often produced from burning of fossil fuels, also from lighting, volcanoes & other biological, non-industrial sources.
“On Earth, most of the nitrogen dioxide is emitted from human-activity like combustion processes from vehicle emissions & fossil-fueled power plants,” says astrobiologist Ravi Kopparapu, from NASA Goddard Space Flight Center.
“Observing NO2 on a habitable planet could potentially indicate the presence of industrialized civilization.”
The presence of NO2 would be called a technosignature, a symbol of technology on an exoplanet outside our solar system. While these planets are too distant to send probes to, so as to we can study them through our increasingly powerful telescopes.
This new study does not involve any observing, but researchers have used computer models to crunch the numbers on-what a NO2 technosignature look like and whether or not our telescopes would-be able to see it based on how nitrogen dioxide absorbs & reflects light.
The researchers found that enormous telescope just like the James Webb Space Telescope would need about 400 hours of observing time at a distance of 30 light years to identify an Earth-like planet near a Sun-like star, one that was producing about much NO2 as we are on our planet. That is a long observation shift, but not outside the-bounds of possibility.
The team of researchers also suggests, NO2 would be a better technosignature than chlorofluorocarbons (CFCs), which considered before; CFCs do not occur in nature so they are less likely to fool-us compared to NO2, but they could not be a common enough indicator for us to look for.
“As far as we know, CFCs aren’t produced-by biology at all, in order that they are a more obvious technosignature than NO2,” says astrobiologist Jacob Haqq-Misra from Blue Marble Institute of Science.
“However, CFCs are very specific manufactured chemicals which may not be prevalent elsewhere; NO2, by comparison, is a general byproduct of any combustion process.”
During the course of their calculations, researchers found that K & M-type stars are cooler & more common than our Sun, would give-off a stronger, more easily detected NO2 signal, because they produce less interfering ultraviolet light.
With more than 4000 exoplanets discovered over the past 25 years, astronomers have many options to explore and any reliable method which will be used to identify most likely locations for alien civilizations going to be helpful.
However, interpreting light reflections & resulting the data over so great a distance is not easy and we are going to need more advanced models further-down the line, models which can mimic about the presence of clouds or aerosols in the atmosphere, for instance, which may mimic the NO2 technosignature.
“If we observe more NO2 than our models suggest is plausible-from non-industrial sources, then the remaining of the NO2 could be attributed to industrial activity,” says astrobiologist Giada Arney from the NASA Goddard.
“Yet there’s always a possibility of a false positive in the look for life beyond Earth and future work will be needed to make sure confidence in distinguishing true positives from false positives.”