Collisions in space could pose a greater danger due to greenhouse gas pollution.

Recent research suggests that greenhouse gas emissions could influence satellite launches in the future. As pollution accumulates, it causes the upper atmosphere of the Earth to contract, raising the risk of collisions of satellites in orbit. This situation represents a new way in which fossil fuel emissions are affecting everyday aspects of life, particularly as telecommunications companies launch megaconstellations of satellites into space. The availability of space is evidently a limited resource that requires more careful management as climate change makes it even more constrained, the authors of the study point out.

William Parker, the lead author of the research and a doctoral candidate at the Massachusetts Institute of Technology, states that we have reached the end of the belief that "space is big." He asserts that the issue of space sustainability directly impacts people, an aspect that is often not understood.

Greenhouse gas emissions trap heat in the lower atmosphere, increasing average global temperatures. However, in the upper atmosphere, there is a decrease in temperature, causing cooling and contraction. Parker uses the metaphor of a balloon shrinking when placed in a freezer to illustrate the phenomenon. A strong atmosphere is crucial for inactive satellites and other debris in orbit to eventually fall, as most burn up upon re-entry. With less dense air, resistance to space debris is reduced, allowing it to remain in orbit longer and increasing the risk of collisions.

The study estimates that the satellite payload capacity could decrease by between 50% and 66% at altitudes of 200 to 1,000 km above the Earth, in the worst-case scenario with high greenhouse gas emissions. Fortunately, there is still time to mitigate the risks. In a mid-range scenario, considered more likely with moderate emissions, the payload capacity could decrease by between 24% and 33%, a significant change that satellite operators will need to consider, especially as low Earth orbit becomes increasingly congested.

Since 1957, approximately 20,650 satellites have been launched, of which around 11,100 are still operational. In the last decade, these numbers have skyrocketed thanks to satellite internet services. SpaceX, for example, plans to send up to 42,000 satellites into orbit. Collisions are a growing concern as space debris increases, and it is reported that SpaceX satellites performed 50,000 collision avoidance maneuvers just in the first half of 2024.

Although there has been previous research on how greenhouse gas emissions affect the upper atmosphere, this study is likely the first to quantify how the decrease in atmospheric density impacts the orbital capacity of low Earth orbit. Parker and his collaborators employed atmospheric models to estimate how many satellites can safely orbit under different emission scenarios. While researcher Petr Šácha notes that other factors could cause short-term anomalies in density, current understanding of how gravitational waves will respond to atmospheric changes is still limited.

Parker seeks to avoid a tipping point where traffic in low Earth orbit triggers cascading collisions, which could result in the loss of access to certain areas of space, similar to a road closure following an accident on a highway. Humanity currently relies on satellites for many everyday services, from GPS navigation to weather forecasting. "We all want to ensure that future generations can benefit from what we get from space," Parker concludes. The goal of this study is to raise public awareness about space sustainability and underscore the importance of managing this limited resource.