As the number of satellites in low Earth orbit continues to grow, a new study warns that greenhouse gas emissions could exacerbate the risk of collisions in space. The research, published in Nature Sustainability, suggests that the buildup of greenhouse gases in the atmosphere could lead to a contraction of the upper atmosphere, reducing the drag on space debris and increasing the likelihood of satellite collisions.

The study's lead author, William Parker, a PhD candidate at the Massachusetts Institute of Technology, notes that the finite nature of space is often overlooked. "We've really reached the end of that era of 'space is big,'" Parker says. "People don't realize that the space sustainability issue is really an issue that impacts them directly." As the atmosphere becomes less dense, it reduces the natural cleanup process of dead satellites and debris, allowing them to linger in orbit for longer and increasing the risk of collisions.

The research estimates that satellite carrying capacity could decline by 50 to 66 percent between the altitudes of 200 and 1,000 km above Earth in a worst-case scenario, with high greenhouse gas emissions continuing to rise. Even in a more moderate scenario, carrying capacity would still decrease by 24 to 33 percent. This reduction in capacity would have significant implications for satellite operators, particularly as the number of satellites in low Earth orbit continues to grow rapidly.

SpaceX's Starlink constellation alone plans to launch up to 42,000 satellites into orbit, adding to the already crowded environment. In the first half of 2024, SpaceX satellites performed 50,000 collision avoidance maneuvers to avoid other spacecraft and debris. As greenhouse gas emissions increase, the risk of collisions will only grow, highlighting the need for sustainable space management practices.

While this study is the first to quantify the impact of decreasing atmospheric density on satellite collisions, it builds on previous research into the effects of greenhouse gas emissions on the upper atmosphere. Petr Šácha, a researcher in the atmospheric physics department at Charles University, notes that there are still uncertainties in the research, particularly regarding the response of gravity waves to atmospheric changes caused by greenhouse gas emissions.

However, the study's authors emphasize the importance of raising awareness about the finite nature of space and the need for sustainable practices. "We all want to make sure that future generations are able to take advantage of the benefits that we get from space," Parker says. As the reliance on satellites for everyday services like GPS and weather forecasts continues to grow, it is essential to address the risks posed by greenhouse gas emissions to ensure the long-term sustainability of space exploration and utilization.

The study's findings serve as a warning to the satellite industry and policymakers to take proactive steps to mitigate the risks of satellite collisions and promote sustainable space management practices. As the world continues to rely on space-based technologies, it is crucial to address the environmental implications of human activities in space and ensure a safe and sustainable future for space exploration.