NASA could look for aliens by searching for pollution in exoplanets’ atmospheres

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On Earth, the industrial age has led to a surge in nitrogen dioxide (NO2) – a major air pollutant which is ploughed into the atmosphere during the burning of fossil fuels. If another civilisation on a different planet had a similar industrial boom, they too would likely have an abundance of NO2 or other pollutants in its atmosphere.

A new study from NASA has shown that scientists could begin observing the atmosphere of other planets for NO2.

Ravi Kopparapu of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said: “On Earth, most of the nitrogen dioxide is emitted from human activity—combustion processes such as vehicle emissions and fossil-fueled power plants.

“In the lower atmosphere (about 10 to 15 kilometres or around 6.2 to 9.3 miles), NO2 from human activities dominate compared to non-human sources.

“Therefore, observing NO2 on a habitable planet could potentially indicate the presence of an industrialised civilisation.”

Experts have so far discovered more than 4,000 planets in the Milky Way which could be habitable as they have the right conditions – mainly being a suitable distance from their host star.

As these planets are so far away, they would be impossible to reach using current technology.

However, experts can use powerful telescopes to examine the atmospheres of distant worlds.

Scientists look at the biosignature of planets, which is an indication of life through gasses, such as oxygen and methane.

However, they can also look for technosignatures, which include NO2 which would likely indicate the burning of fuels on a planet.

As part of a new study, NASA scientists looked at whether NO2 would give off a strong enough signal to be detected from Earth.

NO2 in the atmosphere absorbs some wavelengths of visible light.

This means that if scientists were to look for NO2, they would look for reflections of light from a planet and determine which wavelengths are shorter.

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The research found that if a civilisation is producing as much NO2 as we do on Earth, it “could be detected up to about 30 light-years away with about 400 hours of observing time using a future large NASA telescope observing at visible wavelengths”.

Giada Arney of NASA Goddard said: “On Earth, about 76 percent of NO2 emissions are due to industrial activity.

“If we observe NO2 on another planet, we will have to run models to estimate the maximum possible NO2 emissions one could have just from non-industrial sources.

“If we observe more NO2 than our models suggest is plausible from non-industrial sources, then the rest of the NO2 might be attributed to industrial activity.

“Yet there is always a possibility of a false positive in the search for life beyond Earth, and future work will be needed to ensure confidence in distinguishing true positives from false positives.”

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