Le Monde: Are space activities threatening the upper atmosphere?
Summary of my interview on the atmospheric impacts of spacecraft re-entry.
As if the list of ecological challenges we face wasn’t already long enough, Le Monde exposes in this article a relatively new threat that many will discover for the first time: the consequences of space activities on the upper atmosphere.
Why talk about it now?
The novelty lies in the drastic change in scale represented by the deployment of satellite mega-constellations like Starlink, which aim to provide low-latency internet access everywhere on the planet.
The quest for the lowest possible latency leads to placing these satellites at very low altitudes, which mechanically increases the total number of satellites required to ensure global coverage. As a result, Starlink plans for up to 42,000 satellites, each eventually weighing between 740 and 1,250 kg [Update: now up to 2 tons in 2026!], with a short lifespan of about 5 years. This has earned them the nickname “space Kleenex.”
To understand the colossal nature of this project, these figures must be put into perspective with the history of the space sector:
- Between the launch of the first satellite, Sputnik, and the start of Starlink’s deployment in 2019, nearly 9,000 satellites were launched. The same number has been launched between 2019 and today.
- To maintain Starlink, approximately 8,400 tons would need to be placed in orbit every year—20 times more than the entirety of space activities in 2019.
It is in this context that the article warns about the consequences of increasing metallic particle emissions caused by the reentry of these satellites. Injected into the mesosphere (between 50 and 90 km altitude), these particles gradually descend until they reach the stratosphere, where they cause various disruptions (ozone depletion, cloud formation, etc.), the magnitude of which has not yet been quantified. Since this migration potentially occurs over a long period (up to 30 years), there is a dangerous delay between the emissions and their consequences.
Of course, it is possible—and even highly desirable at this stage—that these consequences turn out to be benign. But as I emphasize in the article, the precautionary principle should prevail. Although unlikely in practice, a moratorium on the deployment of these mega-constellations would give scientists time to do their work, allow regulators to draw eventual conclusions, and perhaps enable citizens to democratically debate the utility of these satellites.
This also applies to the climate effects caused by rocket emissions during launch, which, although uncertain, are better identified and understood than the impact of reentry. The same goes for the damage caused to astronomy and, more generally, to humanity’s common heritage: the night sky, a subject addressed in another article published simultaneously by Le Monde.