Humanity’s trash can be found from the ocean’s deepest depths to the solar system’s outer reaches. Now, it’s been discovered metallic aerosols from burnt-up space junk are polluting our stratosphere. And perhaps even those of other planets.
Purdue University researchers have been flying aircraft fitted with atmospheric “sniffing” devices 19km above Alaska. The samples have unexpectedly returned significant traces of refined metals.
“Just to get things into orbit, you need all this fuel and a huge body to support the payload,” warns Professor Dan Cziczo, whose team has just published their findings in the Proceedings of the National Academy of Sciences.
“There are so many rockets going up and coming back and so many satellites falling back through the atmosphere that it’s starting to show up in the stratosphere as these aerosol particles,” says Cziczo.
“Like the wakes of great ships trolling through the ocean, rockets leave behind them a trail of metals that may change the atmosphere in ways scientists don’t yet understand.”
Dealing with rocket pollution
Signs of aerosol metals aren’t entirely unexpected.
Some 50 to 100 tonnes of meteoroids and interplanetary dust burn up on impact every day.
We have a good idea of what the building blocks of the solar system are. And scientists have been watching “meteor smoke” for decades to further refine this.
“Scientists recently started noticing that the chemical fingerprint of these meteoritic particles was starting to change, which made us ask, ‘Well, what changed?’ because meteorite composition hasn’t changed. But the number of spacecraft has,” says Cziczo.
The researchers found more than 20 elements appearing in far higher ratios than expected. And those elements feature prominently in spacecraft construction.
Lithium. Aluminium. Copper. Lead.
The quantities of these floating about as aerosols in the upper reaches of our atmosphere far outweigh the amounts expected to be produced by cosmic dust.
“The archaeological record of human activities in space is now represented in the upper atmosphere,” Flinders University space archaeologist Dr “Space Junk” Alice Gorman told Cosmos. “You could call it part of the technosphere – thirty trillion tons of human-manufactured materials, according to geologist Jan Zalasiewicz, circulating between space and Earth. It’s a system in the same way we think of an ecology.”
For example, just one aluminium-lithium alloy SpaceX Falcon 9 rocket weighs 550 tons.
Some 270 of these have been launched over the past 13 years. And that rate is expected to only accelerate.
But the metallic aerosol metals appear to be contaminating the chemistry of Earth’s boundary layers. The report estimates that some 10 per cent of the large sulfuric acid particles that “buffer” the ozone layer now carry aluminium and other spacecraft-associated metals.
With as many as 50,000 low-Earth orbit satellites expected to be in place by 2030, the researchers believe this figure will quickly soar as high as 50 per cent.
Dr Gorman says the potential impact may extend beyond our own planet.
“The Galileo mission sent a probe and an orbiter into Jupiter’s atmosphere, and NASA’s Juno spacecraft is set to de-orbit in 2025,” she explains. “The Cassini spacecraft fell into Saturn’s atmosphere in 2017. Mars has a much thinner atmosphere than Earth, but it’s likely a few orbiters have fallen out of orbit and burnt up after their mission life was over.
‘There is unlikely to be any impact on other planets at this stage but it’s something to be aware of in future missions.’
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