Findings in the Stratosphere
Researchers have made remarkable and initially mysterious discoveries more than 11 kilometers above the Earth’s surface: they have stumbled across various metals usually not found naturally. This finding leads researchers to an alarming conclusion.
Origins of the Metals
The indications are that these metallic particles originate from satellites and rocket stages that have fallen back into the Earth’s atmosphere, evaporating under the force of intense friction and heat. Thus, for the first time, concrete evidence has been found that space debris also pollutes our stratosphere. This is discussed in the journal “Proceedings of the National Academy of Sciences”.
Behind the SABRE Investigation
The researchers base their conclusion on a research mission referred to as SABRE, which stands for Stratospheric Aerosol processes, Budget and Radiative Effects. In this mission, an airplane equipped with a highly sensitive instrument developed specifically for this investigation, is taken up to a height of approximately 11 kilometers, for the purposes of investigating aerosols (tiny dust or liquid particles floating in the air) that exist within the operation of our climate and the well-known ozone layer.
The Mysterious Elements
The investigation leads to a noteworthy conclusion. It appears that as much as 10 percent of the sulfuric acid particles, which make up a significant portion of the particles in the stratosphere, harbor aluminum and exotic metals. “Two of the most surprising elements we found in these particles were niobium and hafnium,” says researcher Daniel Murphy. “Both of these are rare elements that you do not expect to encounter in the stratosphere. It was a mystery where these metals came from and how they got here.”
Niobium and hafnium do not naturally occur; they are locked within minerals and must be extracted. Humans are willing to make the effort for this extraction, both metals are commonly used in semiconductors and so-called superalloys, which are resistant to high temperatures.
The Space Travel Industry
Along with these two noticeable elements, the researchers also found copper, aluminum, and lithium. These elements were present in much higher concentrations than those typically found in meteorites or space-originating grit. This lead researcher Murphy to an idea. “The combination of aluminum and copper, together with niobium and hafnium – which are used in heat-resistant alloys – pointed us towards the space travel industry.” Follow-up research confirmed that the scientists were on the right path. The ratio in which these elements were found in the stratosphere neatly matched the ratio in which they occur in rockets and satellites. This makes the researchers convinced that these elements land in the stratosphere when the objects they have been used in, return to the earth and evaporate in the Earth’s atmosphere.
The Effect
In total, the researchers discovered over 20 different elements that can be traced back to spacecraft and satellites. These elements include copper, aluminum, niobium, and hafnium, as well as silver, iron, magnesium, nickel, and zinc. It is still unknown to what extent they actually affect the stratosphere. Subsequent research is required to determine if and how they interact with other aerosols in the stratosphere and whether they might also impact the ozone layer.
More Satellites
Such follow-up research is certainly not insignificant, the researchers emphasize. The number of satellites in low orbit around the Earth – thus eventually due to fall back to Earth and burn in the atmosphere – is increasing at a rapid pace. “About ten percent of stratospheric aerosols harbor metals; that’s not much,” states researcher Martin Ross. “But in the past 5 years, over 5000 satellites have been launched. Most of them will return to Earth in the next five years. We need to know how this could potentially influence stratospheric aerosols.”
Space Debris Removal
The latter is also vitally important in light of plans to start removing space debris – defunct satellites and forgotten rocket boosters that circulate in higher orbits around the Earth. Such efforts include ESA’s working on a spacecraft that ‘catches’ these satellites and pulls them into the atmosphere, where they evaporate. While this will make the space cleaner, the stratosphere may indeed become more polluted, as suggested by this new research. It provides a good reason to quickly determine the impact of the particles, left behind in the stratosphere after the burning of space debris, on our atmospheric environment.
