Climate change, often associated with its effects on Earth, could well impact the space near our planet. A recent study reveals that greenhouse gas emissions risk significantly reducing the capacity for satellites in low Earth orbit by the end of the century.
Researchers at the Massachusetts Institute of Technology (MIT) have discovered that the increase in greenhouse gases cools and contracts the thermosphere, the atmospheric layer where most satellites operate. This contraction reduces the density of the atmosphere, thereby decreasing the phenomenon of "atmospheric drag" that helps remove space debris. Indeed, atmospheric drag acts as a frictional force, slowing down objects in orbit and causing them to gradually descend until they burn up in the denser layers of the atmosphere.
A domino effect in space
The thermosphere, located between 85 and 600 kilometers (53 and 373 miles) in altitude, plays an important role in managing space debris. The atmospheric drag it generates helps slow down orbiting objects, causing them to descend and burn up in the atmosphere. However, with the contraction of this layer, debris remains in orbit longer, increasing the risk of collisions.
This reduction in atmospheric drag has direct consequences on the longevity of space debris. Normally, objects in low Earth orbit gradually lose altitude and eventually disintegrate. But with a less dense atmosphere, this process slows down, leaving debris floating for decades, or even centuries.
a) Potential reduction in thermosphere density in low Earth orbit according to the SSP1–2.6 scenario.
b) Reduction according to the SSP2–4.5 scenario.
c) Reduction according to the SSP5–8.5 scenario.
d) Thermosphere density at 600 km, including a projection of the solar cycle and the secular reduction in density related to SSPs. The researchers' simulations show that, in a high-emissions scenario, the capacity for satellites in low Earth orbit could decrease by 50 to 66% by 2100. Applying the projection to a range of 400 to 1000 kilometers (249 to 621 miles) in altitude, this reduction could even reach 82%. This decline could lead to increasing instability, with a risk of cascading collisions, rendering certain orbital zones unusable.
Such a situation would threaten essential services provided by satellites, such as communications and climate monitoring.
Uncontrolled growth of satellites
The number of satellites in low Earth orbit has exploded in recent years, particularly with the deployment of constellations to provide internet. In 2023, over 10,000 satellites were active, and this number continues to grow. This rapid growth, combined with the reduction in orbital capacity, poses a major challenge for the sustainable management of space.
Mega-constellation projects, such as Starlink or OneWeb, plan to launch thousands of additional satellites in the coming years. These initiatives, while useful for improving global connectivity, risk worsening the saturation of low Earth orbit. Without strict regulation, the density of objects in orbit could reach a critical point, increasing the risk of collisions to the point of making the thermosphere unusable (a scenario known as the "Kessler Syndrome").
Researchers emphasize the urgency of taking measures to limit greenhouse gas emissions and better regulate the number of satellites launched. Without concerted action, low Earth orbit could become too crowded, compromising the essential services these satellites provide, such as communications and climate monitoring. Proactive management is needed to avoid irreversible orbital instability.
To go further: What is the Kessler Syndrome?
The Kessler Syndrome describes a scenario where collisions between orbiting objects generate so much debris that space gradually becomes unusable. Each collision creates new fragments, exponentially increasing the risk of future collisions. This phenomenon could render certain orbits inaccessible for decades.
This scenario was popularized by Donald J. Kessler, a NASA scientist, in the 1970s. It highlights the risk of a chain reaction where space debris, multiplying, would make Earth's orbit too dangerous for operational satellites. Such a situation would threaten essential services like communications, navigation, and Earth observation.
Today, with the rapid increase in the number of satellites and the reduction in atmospheric drag due to climate change, the risk of Kessler Syndrome becomes more concerning. Scientists are calling for international regulation and space cleanup technologies to prevent this potential catastrophe.
Article author: Cédric DEPOND