In a groundbreaking revelation, National Oceanic and Atmospheric Administration (NOAA) scientists have uncovered an unexpected presence of metal-infused particles in the stratosphere, well over seven miles above Earth’s surface. These particles, containing various metals from satellites and spent rocket boosters, have been vaporized by the intense heat generated during re-entry into Earth’s atmosphere.
This discovery is one of the initial findings stemming from the analysis of data collected during a high-altitude research mission by NOAA’s Chemical Science Laboratory, known as SABRE (Stratospheric Aerosol processes, Budget and Radiative Effects). SABRE represents NOAA’s most ambitious and extensive effort to investigate aerosol particles in the stratosphere—a critical atmospheric layer that moderates Earth’s climate and houses the protective ozone layer.
Scientists used an exceptionally sensitive custom-built instrument, located at NOAA’s Boulder, Colorado facility, and mounted within the nose of a NASA WB-57 research aircraft. Their findings revealed the presence of aluminium and exotic metals embedded within approximately 10 percent of sulphuric acid particles, which constitute the majority of particles in the stratosphere. Furthermore, researchers managed to correlate the composition of these rare elements with the special alloys utilized in rockets and satellites, confirming their source as metal vaporized from spacecraft re-entering Earth’s atmosphere.
Notably, this significant discovery was published on October 16 in the Proceedings of the National Academy of Sciences.
“Two of the most surprising elements we saw in these particles were niobium and hafnium,” noted Daniel Murphy, research chemist at the Chemical Sciences Laboratory, who led a collaborative team from CIRES, Purdue, and the University of Leeds. “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.”
The SABRE mission cantered on aerosols, minute particles that either absorb or reflect the Sun’s rays, serving to shield Earth. Under specific conditions, they can also contribute to ozone-destroying chemical reactions. This remarkable discovery by NOAA scientists marks the first direct link between stratospheric pollution and the re-entry of space debris.
CHEMICAL COMPOSITION OF PARTICLES
Notably, niobium and hafnium are not naturally occurring free elements but are refined from mineral ores. They find applications in semiconductors and super alloys.
Apart from these two unusual elements, a significant number of particles contained copper, lithium, and aluminium, with concentrations far exceeding what’s typically found in meteoric ‘space dust.’ Murphy observed, “The combination of aluminium and copper, plus niobium and hafnium, which are used in heat-resistant, high-performance alloys, pointed us to the aerospace industry.”
In total, over 20 distinct elements linked to spacecraft and satellite re-entries were identified by NOAA scientists during the SABRE mission, including silver, iron, lead, magnesium, titanium, beryllium, chromium, nickel, zinc, and lithium. The precise identification of these various metals was possible through a custom-built instrument named PALMS (Particle Analysis by Laser Spectrometry), which meticulously analyzes individual airborne particles in-flight. PALMS ingests these particles, measures their size and speed with detecting laser beams, and then vaporizes them with a high-powered laser, followed by mass spectrometry analysis to determine the exact atomic composition of each particle.
This discovery raises critical questions regarding how these aerospace debris particles interact with other stratospheric aerosols, particularly in light of the anticipated increase in space traffic and its potential impact on the ozone layer. Additionally, scientists aim to understand how potential future proposals to release millions of tons of sulphur aerosols into the stratosphere to combat global warming may be affected by these newly discovered particles.
The presence of aerospace metals in the stratosphere may hold implications for ongoing and future space activities, particularly as thousands of satellites continue to be launched and subsequently re-enter the Earth’s atmosphere, potentially increasing the proportion of stratospheric aerosols containing metal cores. Researchers emphasize the need for further study to fully comprehend the consequences of these novel metals in the stratosphere.
As of October 4, there are 8,697 satellites currently in orbit, with 7,892 of them in low Earth orbit—many of which are destined to burn up upon re-entry into the atmosphere.
Martin Ross, co-author of the study from The Aerospace Corporation, remarks, “At 10%, the current fraction of stratospheric aerosol with metal cores is not large. But over 5,000 satellites have been launched in the past five years. Most of them will come back in the next five, and we need to know how that might further affect stratospheric aerosols.”