Now we can blame spacecraft for polluting the atmosphere

A group of scientists studying the effects of rocket and satellite reentry vaporization in Earth's atmosphere have found some startling evidence that could point to disastrous environmental effects on the horizon. 

The study, published in the Proceedings of the National Academy of Sciences, found that around 10 percent of large (>120 nm) sulfuric acid particles in the stratosphere contain aluminum and other elements consistent with the makeup of alloys used in spacecraft construction, including lithium, copper and lead. The other 90 percent comes from "meteoric smoke," which are the particles left over when meteors vaporize during atmospheric entry, and that naturally-occurring share is expected to plummet drastically. 

"The space industry has entered an era of rapid growth," the boffins said in their paper, "with tens of thousands of small satellites planned for low earth orbit. 

"It is likely that in the next few decades, the percentage of stratospheric sulfuric acid particles that contain aluminum and other metals from satellite reentry will be comparable to the roughly 50 percent that now contain meteoric metals," the team concluded. 

Atmospheric circulation at those altitudes (beginning somewhere between four and 12 miles above ground level and extending up to 31 miles above Earth) means such particles are unlikely to have an effect on the surface environment or human health, the researchers opined. 

Stratospheric changes might be even scarier, though

Earth's stratosphere has classically been considered pristine, said Dan Cziczo, one of the study's authors and head of Purdue University's department of Earth, atmospheric and planetary studies. "If something is changing in the stratosphere - this stable region of the atmosphere - that deserves a closer look."

One of the major features of the stratosphere is the ozone layer, which protects Earth and its varied inhabitants from harmful UV radiation. It's been harmed by human activity before action was taken, and an increase in aerosolized spacecraft particles could have several consequences to our planet.

One possibility is effects on the nucleation of ice and nitric acid trihydrate, which form in stratospheric clouds over Earth's polar regions where currents in the mesosphere (the layer above the stratosphere) tend to deposit both meteoric and spacecraft aerosols. 

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Ice formed in the stratosphere doesn't necessarily reach the ground, and is more likely to have effects on polar stratospheric clouds, lead author and National Oceanic and Atmospheric Administration scientists Daniel Murphy told The Register.

"Polar stratospheric clouds are involved in the chemistry of the ozone hole," Murphy said. However, "it is too early to know if there is any impact on ozone chemistry," he added

Along with changes in atmospheric ice formation and the ozone layer, the team said that more aerosols from vaporized spacecraft could change the stratospheric aerosol layer, something that scientists have proposed seeding in order to block more UV rays to fight the effects of global warming. 

The materials being injected from spacecraft reentry is much smaller than amounts scientists have considered for intentional injection, Murphy told us. However, "intentional injection of exotic materials into the stratosphere could raise many of the same questions [as the paper] on an even bigger scale," he noted.

A larger share of more metals (20 such materials vaporized from spacecraft were found in the study) could also cause "novel stratospheric chemistry or unusual optical properties." Murphy told us that such optical properties are "more of a technical point," and unlikely to be visible like the sort of changes after a major volcanic eruption.

Nonetheless, "we have not identified any definite implications of the presence of these metals in stratospheric sulfuric acid particles," the team concluded. Whether we want to gamble with those odds as we vaporize more spacecraft in the coming decades is something we need to grapple with - and soon, the team opined. 

"There is an urgent need for research into which materials may be benign and which may have impacts on the stratosphere," Murphy told us. ®