MIT aerospace engineers have discovered that greenhouse gas emissions are affecting near-Earth space in surprising ways. Their research indicates that, over time, these emissions could limit the number of satellites that can operate sustainably.
According to a study published in Nature Sustainability, greenhouse gases like carbon dioxide can cause the upper atmosphere to shrink. This is critical in the thermosphere, where the International Space Station and many satellites orbit. As the thermosphere contracts, the density decreases, which lessens atmospheric drag. This drag normally helps pull old satellites and debris down, allowing them to burn up in the atmosphere.
With reduced drag, things in orbit stay up longer. This means space junk will linger in valuable regions and raises the risk of collisions between satellites. The researchers ran simulations to see how carbon emissions might influence the capacity for satellites in low Earth orbit. They predict that by 2100, the most popular orbital zones could see a carrying capacity drop by 50-66% because of these environmental changes.
Study author Richard Linares, a professor at MIT, noted, “What we do on Earth with greenhouse gases now affects how we can operate satellites in the future.” His colleague William Parker added, “The upper atmosphere is delicate. Climate change is disrupting its balance at a time when we are launching more satellites than ever.”
This increase in satellite launches, especially for internet services, poses a challenge. If we do not manage emissions and satellite activity, space could become overcrowded, potentially leading to more collisions and debris.
The thermosphere naturally expands and contracts in an 11-year cycle, influenced by solar activity. When solar radiation is low, the thermosphere cools and contracts, while it expands during solar maximum. In the 1990s, scientists began to study how greenhouse gases might impact this cycle. They discovered that while these gases trap heat in the lower atmosphere, they cool the thermosphere at higher altitudes. This cooling leads to a contraction of the thermosphere, decreasing atmospheric density in those regions.
In recent years, scientists have observed changes in satellite drag, indicating a contraction of the thermosphere beyond the natural solar cycle effects. Parker remarked, “The sky is literally falling, albeit at a slow rate that takes decades to manifest.”
Currently, there are over 10,000 satellites in low Earth orbit, which extends up to 1,200 miles (2,000 kilometers) above Earth. These satellites are crucial for services like weather forecasting, communications, and navigation. The rapid increase in satellites means operators must frequently adjust their positions to prevent collisions. Any crash generates debris that can stay in orbit for years, raising the risk of further accidents.
In their study, the researchers modeled various greenhouse gas emission scenarios to explore their impact on atmospheric density and satellite safety. They employed an approach similar to ecological studies, defining a “carrying capacity” for orbital zones. This helped them assess how many satellites low Earth orbit can safely manage.
The team examined different futures, comparing a constant emissions scenario from the year 2000 to others based on projected increases in greenhouse gases. They found that ongoing emissions would significantly reduce the allowable number of satellites in the coming decades.
By 2100, they estimate that regions between 200 and 1,000 kilometers in altitude could hold 50-66% fewer satellites compared to a scenario where emissions remained at 2000 levels. If these limits are surpassed, the researchers warned of a “runaway instability,” where collisions generate so much debris that future satellite operations become unfeasible.
Notably, some orbital regions are already quite crowded, especially with recent large groups of satellites, like SpaceX’s Starlink, which includes thousands of small satellites.
Parker emphasized, “The megaconstellation trend shows that climate change will reduce our satellite capacity in orbit, and we’re nearing those limits now.” Linares added, “The atmosphere helps clear our debris. If it changes, the environment for debris will change too.” They concluded that managing greenhouse gas emissions is crucial for the long-term future of satellite operations and space sustainability.
This important research was funded by the U.S. National Science Foundation, the U.S. Air Force, and the U.K. Natural Environment Research Council.
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