When a multi-ton spacecraft blows up mid-air, you can't just brush aside its environmental impact.
Following the explosion of the upper stage of SpaceX's Starship, which sent fiery streaks of debris raining over the Caribbean last month, a scientist warned that the rocket's spectacular demise may have caused significant amounts of atmospheric pollution.
"This event potentially released an estimated 45.5 tonnes of metal oxides and 40 tonnes of reactive nitrogen into the upper atmosphere," wrote University College London researcher Connor Barker in a LinkedIn post, which was highlighted this week by Space.com.
That's about 35 percent of all the aluminum that enters the atmosphere from meteors every year, Barker estimated. The researcher recently published a catalog of air pollutant emissions associated with rocket launches.
He stressed in an email to Space.com, however, that the numbers are preliminary. And according to astronomer Jonathan McDowell, "many tons" of the debris probably fell in the ocean instead of burning up in the atmosphere, he told the website, so the numbers put forth by Barker are likely the upper end of the damage spectrum.
The "rapid unscheduled disassembly" occurred during the rocket's seventh orbital flight test on January 16. While the 85-ton spacecraft was performing an ascent burn after separating from its booster, control lost contact with the vehicle, before it exploded roughly eight and a half minutes after liftoff.
SpaceX CEO Elon Musk claimed that a propellant leak was likely responsible, though a full investigation is still ongoing.
Whatever the cause, it had immediate, dramatic consequences. Dozens of flights were diverted to avoid the falling remains, with the Federal Aviation Administration creating a "debris response era" to keep aircraft away.
And everything didn't harmlessly fall into the sea, either. Some of the debris showered down on a nearby island, with residents discovering shards of the rocket alarmingly close to their homes.
But if Barker's onto something, we should also be worrying about what didn't fall to Earth.
It would echo concerns raised by other scientists about the serious amounts of aluminum oxides and other harmful pollutants released by another SpaceX venture, Starlink, whose thousands of expendable satellites are designed to burn up in the atmosphere.
Some research has suggested that aluminum oxides may be contributing to ozone depletion. A controversial paper has also raised the possibility that metallic particles released by the satellites could even weaken the Earth's magnetic field.
We should note, though, that this is a spacefaring problem, and not just a SpaceX one; the authors of the magnetic field paper estimated that the amount of metallic particles in our atmosphere has increased by a millionfold since the start of the space age.
As Space.com notes, there is a silver lining. Unlike SpaceX's other spacecraft, Starship's upper stage is made of stainless steel, not aluminum. That doesn't mean it didn't produce other harmful oxides, though, as Barker speculated. It very likely did — but it could've been even worse.
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