Minuscule traces of metal from space junk that's designed to be disposable are invisibly polluting the Earth's atmosphere, a new study has found.
In recent times, spacecrafts launched into space have been designed so that they fall out of orbit and fall back down to Earth after their intended use.
So instead of the materials crashing on land, they can burn up in the upper atmosphere.
Although the debris of rockets and satellites burn up when re-entering the planet's atmosphere, the consequences of metal vapour being left behind currently remain unknown.
But given the amount of space exploration taking place, the amount of metal vapour is expected to rise in the years to come.
Physicist Daniel Murphy of the National Oceanic and Atmospheric Administration (NOAA) has led a team of researchers to investigate what effects this metal vapour could have as well as its impact over time and this study was published in Proceedings of the National Academy of Sciences, as per Science Alert.
He listed "iron, silicon, and magnesium from the natural meteoric source" as the current refractory material in stratospheric particular.
Murphy has warned how this composition could be affected by the metal vapour from space junk.
"However, the amount of material from the reentry of upper-stage rockets and satellites is projected to increase dramatically in the next 10 to 30 years," he wrote.
"As a result, the amount of aluminum in stratospheric sulfuric acid particles is expected to become comparable to or even exceed the amount of meteoric iron, with unknown consequences for inclusions and ice nucleation."
To find out if metal vapour remained, Murphy and his team took and analyzed 500,000 stratospheric aerosol droplet samples to see if they had traces of spacecraft metals.
Aerosols contain sulfuric acid droplets made from the oxidation of the carbonyl sulfide gas and in the atmosphere, this can appear naturally or as a pollutant.
Metal and silicon traces can be found in these droplets too, acquired from meteors which vaporize upon atmospheric entry.
Around 20 metals were discovered from this research, and while some metals had similar ratios to the vaporizing meteors, other metals such as lithium, aluminium, copper, and lead exceeded the anticipated amounts.
Particles from vaporized spacecraft were found in 10 per cent of stratospheric aerosols over a certain size while other common spacecraft metals such as niobium and hafnium were also present.
Consequently, these traces of spacecraft particles could affect how water freezes into ice in the stratosphere, and stratospheric aerosol particles could change in size.
Due to more space exploration planned in an "era of rapid growth" for the industry, the researchers predict "the percentage of stratospheric sulfuric acid particles that contain aluminum and other metals from satellite reentry will be comparable to the roughly 50 per cent that now contain meteoric metals."
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