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The Thermosphere’s Role in Managing Space Debris
The thermosphere typically pulls space debris toward its demise. However, as it becomes thinner, there's a chance that disrupted orbits could arise.
One concerning impact of climate change is that Earth's atmosphere is shrinking, which may allow space junk to linger in orbit longer. This could lead to collisions with other debris and create such a mess that low Earth orbits become increasingly problematic.
A rather gloomy forecast was shared on Monday in a Nature Sustainability article titled "Greenhouse gases reduce the satellite carrying capacity of low Earth orbit."
How CO2 Contributes to a Shrinking Thermosphere
Written by researchers from MIT and the University of Birmingham, the paper kicks off with the point: "Human-made greenhouse gas emissions in Earth's atmosphere have been linked to cooling and contraction in the thermosphere."
The thermosphere stretches from around 90 km to 500 km above the planet. Although conditions up there are extreme, it's not a complete vacuum. According to NASA, it has "very low density of molecules," especially when compared to the “extremely low density” of the exosphere.
One of the molecules present in the thermosphere is carbon dioxide (CO2), which transfers heat from the lower atmosphere and then radiates it out.
"As a result, rising levels of CO2 will inevitably cool the upper atmosphere. This cooling leads to a contraction of the global thermosphere, resulting in reduced mass density at the same altitude over time."
The Growing Risk of Space Debris and Kessler Syndrome
That's concerning because even the low density in the thermosphere is enough to create drag on satellites in low Earth orbit—so much so that the International Space Station needs regular boosts to maintain its position.
This drag is also sufficient to gradually slow down space debris, causing it to fall into thicker parts of the atmosphere, where it burns up. The authors caution that a less dense thermosphere could mean more space junk hanging around for extended periods, raising the risk of Kessler syndrome. This scenario involves debris colliding with other debris and breaking into smaller fragments, leading to such a proliferation of space junk that certain orbits become unsafe for satellites.
This situation is particularly troubling, especially since we're heavily relying on low Earth orbit for services like broadband satellites.
What Can Be Done to Prevent a Space Junk Crisis?
The paper suggests we might need to rethink our plans before too long.
"Modeled CO2 emissions scenarios from 2000 to 2100 indicate a potential 50-66 percent decrease in satellite carrying capacity between altitudes of 200 and 1,000 km."
On a positive note, the paper points out that satellite manufacturers are aware of the possibility of Kessler syndrome and often design their systems with collision avoidance features to dodge debris.
The authors hope that manufacturers and operators can collaborate on various debris-reduction strategies and that greenhouse gas emissions are curtailed to keep the thermosphere in good shape.