The ongoing surge of greenhouse gas emissions in the near-Earth environment could cause dramatic declines in the number of satellites orbiting the planet by the end of the century, a new study has found.
By the year 2100, the “satellite carrying capacity” of the most popular low-orbit regions could decline by 50 to 66 percent due to the impacts of these emissions, according to the study, published on Monday in Nature Sustainability.
“Our behavior with greenhouse gases here on Earth over the past 100 years is having an effect on how we operate satellites over the next 100 years,” senior author Richard Linares, an associate professor at the Massachusetts Institute of Technology, said in a statement.
Linares and his colleagues determined that carbon dioxide and other greenhouse gases can cause the upper atmosphere to shrink.
The researchers found that the contraction of the thermosphere — the atmospheric layer where the International Space Station orbits today — causes a plunge in density, leading to ripple effects.
Specifically, that decrease in density reduces “atmospheric drag,” or a force that pulls old satellites and other debris down to altitudes where they will combust from interactions with air molecules.
Less drag, therefore, means longer lives for “space junk,” which the researchers said would litter popular orbital regions for decades and raise the risk of collisions.
“The upper atmosphere is in a fragile state as climate change disrupts the status quo,” lead author William Parker, an MIT graduate student, said in a statement.
Despite this fragility, there has been a significant surge in the number of satellites launched in recent years, particularly for delivering broadband Internet from space, Parker explained.
“If we don’t manage this activity carefully and work to reduce our emissions, space could become too crowded, leading to more collisions and debris,” he added.
The thermosphere naturally contracts and expands every 11 years in response to the sun’s routine activity cycle, the scientists noted. When that activity is low, the Earth receives less radiation, and the outermost atmospheric layer cools and contracts before expanding again.
While modeling from the 1990s already showed that greenhouse gases trap heat in the lower atmosphere, more recent research determined that the same gases also radiate heat at much higher altitudes — thereby cooling the thermosphere.
Yet only in the past decade have scientists been able to measure shifts in satellite drag, indicating that the thermosphere could be contracting in response to influences other than the sun’s natural cycle, the authors explained.
“The sky is quite literally falling,” Parker said.
Today, more than 10,000 satellites are in low orbit, or up to 1,200 miles from the Earth’s surface, per the study. And while these satellites deliver essential services to humans, collisions among them can generate debris that stays in orbit for decades or centuries, the authors warned.
Aiming to understand whether the current trajectory is sustainable long-term, the scientists simulated different greenhouse gas emissions scenarios over the next century.
For each altitude range of interest, they modeled the orbital dynamics and the threat of satellite collisions, based on the number of objects floating in that area. Through this approach, the researchers could identify each range’s “carrying capacity,” or the number of satellites that could be supported.
Ultimately, they estimated that the number of satellites that could be safely accommodated within the altitudes of 124 to 621 miles might plunge by 50 to 66 percent — if emissions remain at year-2000 levels.
If satellite capacity were to be exceeded, the researchers forecasted that a given area could experience what’s known as a “runaway instability,” or a cascade of collisions that would close the range to safe satellite operations.
“We rely on the atmosphere to clean up our debris. If the atmosphere is changing, then the debris environment will change too,” Parker said. “We show the long-term outlook on orbital debris is critically dependent on curbing our greenhouse gas emissions.”
