Elon Musk’s SpaceX has announced it will get rid of 100 Starlink satellites over the next six months after discovering a design flaw that could cause them to malfunction. Instead of posing a threat to other spacecraft, SpaceX will “de-orbit” these satellites so they burn up in the atmosphere.

But atmospheric scientists are increasingly worried that such a clear deviation in the space sector will lead to further changes in the climate on Earth. Recently, a team unexpectedly discovered potentially ozone-depleting metals in spacecraft in the stratosphere, the layer of atmosphere where the ozone layer forms.

Relative “low Earth orbit”, which houses satellites monitoring Earth’s ecosystems, is becoming increasingly cramped; Starlink alone has more than 5,000 spacecraft in orbit. Therefore, clearing debris is a priority for the space industry. Newly launched spacecraft must also be deorbited within 25 years (the US recently implemented a stricter five-year rule), either by moving into a “graveyard orbit” or by descending into Earth’s atmosphere.

Low-orbit satellites are generally designed to use remaining fuel and Earth’s gravity to re-enter the atmosphere. In a controlled entry, a spacecraft enters the atmosphere at a predetermined time and lands in the farthest part of the Pacific Ocean at Point Nemo (also known as the spacecraft graveyard). In an uncontrolled reentry, the spacecraft is left to die a “natural death” and burn up in the atmosphere.

NASA and the European Space Agency support this form of recycling as part of a design philosophy called “design for death.” Building, launching and operating a satellite that is durable enough to operate in hostile space, yet can easily disintegrate and burn during re-entry to prevent hazardous debris from reaching the Earth’s surface, is an environmental challenge. Work is still continuing.

Satellite operators must prove that their designs and reentry plans have a low level of “human hazard” before a license is granted. However, there is limited concern about the impact on the Earth’s upper atmosphere during the re-entry phase. This is not an oversight.

Initially, neither the space industry nor the astrophysics community considered the burn-up caused by satellite reentry to be a serious environmental threat; At least for the atmosphere. After all, the amount of particles ejected by spacecraft is small compared to the 440 tons of meteoroids that enter the atmosphere every day, along with volcanic ash and anthropogenic pollution from industrial processes on Earth.

Bad news for the ozone layer?

So are atmospheric climatologists overreacting to the presence of spacecraft particles in the atmosphere? Their concerns are based on 40 years of research into the cause of ozone holes at the south and north poles, which were first widely noticed in the 1980s.

Today they know that ozone loss is caused by man-made industrial gases combined with natural and high-altitude polar stratospheric clouds, or nacreous clouds. The surfaces of these ether clouds act as catalysts, converting benign chemicals into more active forms that can quickly destroy ozone.

Dan Chitso is an atmospheric researcher at Purdue University in the US and co-author of a recent study identifying ozone-depleting substances in the stratosphere. The question he explained to me is whether new particles from the spacecraft will help form these clouds and cause ozone loss at a time when Earth’s atmosphere is just beginning to recover.

Of greater concern to atmospheric scientists like Chitso is that only a few new particles could form more such polar clouds; not only in the upper atmosphere, but also in the lower atmosphere, where cirrus clouds form. Cirrus clouds are thin clouds of ice that can be seen over six kilometers into the sky. They tend to let the sun’s heat in, but then trap it on its way out, so theoretically more cirrus clouds could add additional global warming on top of what we’re already seeing from greenhouse gases. However, this is not definitive and is still being investigated.

Chitso also explains that we know from anecdotal evidence that high-altitude clouds over the poles are changing, but we don’t yet know what causes this change. Are these natural particles, such as meteorites or volcanic debris, or unnatural particles from spacecraft? This is what we need to know.

I’m worried but not sure

So how do we answer this question? We have some research from atmospheric scientists, spacecraft designers, and astrophysicists, but it’s not precise enough or focused enough to make informed decisions about which direction to go. Some astrophysicists say that alumina (aluminum oxide) particles in the spacecraft will cause chemical reactions in the atmosphere that will likely lead to ozone depletion.

Atmospheric scientists, who examined the issue in detail, could not make this breakthrough due to the lack of scientific evidence. We know that particles from spacecraft are in the stratosphere. But what this means for the ozone layer or the climate is still unknown.

There is a tendency to exaggerate research findings to gain more support. But this is the road to research hell, and naysayers will then use bad findings to discredit the research. We also do not want populist views to be used. But we have also learned that if we wait until concrete evidence is available, as in the case of ozone depletion, it may be too late. This is a constant dilemma.