Scientists with the National Oceanic and Atmospheric Administration (NOAA) have used new mission data to show that the stratosphere is being polluted by metals from satellites and spent rocket boosters vaporized during re-entry.
NOAA analyzed the data collected by its high-altitude research plane over the Arctic for its Chemical Science Laboratory mission called SABRE. It revealed aluminum and exotic metals embedded in about 10% of sulfuric acid particles, which comprise the large majority of particles in the stratosphere more than 11 km above the surface.
“Two of the most surprising elements we saw in these particles were niobium and hafnium,” announced NOAA chemist Daniel Murphy, who led a team of scientists from CIRES (Cooperative Institute for Research In Environmental Sciences), Purdue and the University of Leeds, in a statement. “These are both rare elements that are not expected in the stratosphere. It was a mystery as to where these metals are coming from and how they’re ending up there,” added Murphy.
Niobium and hafnium are refined from mineral ores and used in semiconductors and superalloys, according to NOAA.
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The research team also found that a significant number of particles contained copper, lithium and aluminum at concentrations exceeding what’s expected in “space dust” or meteorics.
“The combination of aluminum and copper, plus niobium and hafnium, which are used in heat-resistant, high-performance alloys, pointed us to the aerospace industry,” said Murphy.
In all, scientists identified more than 20 distinct elements from spacecraft and satellite re-entry in particles sampled during SABRE, including: silver, iron, lead, magnesium, titanium, beryllium, chromium, nickel, zinc and lithium.
The elements were identified through a custom-built instrument called PALMS, short for Particle Analysis by Laser Mass Spectrometry, which ingests and chemically analyzes individual particles in the air one by one as the aircraft is in flight.
PALMS is installed into the nose cone of the research aircraft with a large forward-facing air intake inlet, according to NOAA. An aerosol particle passes through two detecting laser beams that measure its size and speed. A third high-powered laser is then precisely triggered to vaporize the particle.
NOAA scientists say they are eager to understand how these particles of aerospace debris interact with other aerosols in the stratosphere because of anticipated increases in space traffic and their potential impact on the ozone layer. They also want to explore the impact of possible future proposals to seed the stratosphere with millions of tons of sulfur aerosols to slow the rate of global warming by reflecting sunlight back to space.
“There will be a lot of work to understand the implications of these novel metals in the stratosphere,” explained Murphy.
As of October 4, the tracking website Orbiting Now lists 8,697 satellites currently in orbit, 7,892 of which are in low Earth orbit and are destined to burn up on re-entry.