Analysis results indicate that if greenhouse gas emissions are not suppressed and continue to increase, the number of satellites that can safely orbit the Earth by the end of this century will decrease. The increase in small space debris and remnants of small satellites left in low Earth orbit is expected to lead to a reduction in the safe orbits for satellites. It is noteworthy that without groundbreaking measures to reduce greenhouse gas emissions causing climate change, this could also hinder the emerging space industry and the expansion of national space economies.
Researchers led by Professor William Parker at the Massachusetts Institute of Technology (MIT) reported on the 10th (local time) in the international journal Nature Sustainability that if greenhouse gas emissions continue to rise, the carrying capacity for satellites to orbit in low Earth orbit could decrease by 66% by 2100.
The reusable rocket technology led by SpaceX has brought about a drastic change in the space industry. According to the space industry, recovering and reusing first-stage rockets can launch rockets at a cost that is up to 65% cheaper than traditional rockets used for single use. Reusable rockets have now become the trend in rocket development not only for other launch companies like Blue Origin and Rocket Lab but also for governments around the world. As the number of reusable rocket launches increases, the number of satellites heading to low Earth orbit has also surged significantly in the past decade.
According to the UN Office for Outer Space Affairs (OOSA), the number of satellites orbiting Earth rose from 4,077 in 2015 to 28,300 by 2024. With various services proposed, including low Earth orbit satellite communications that connect the world through Starlink and OneWeb, as well as positioning, navigation, and timing (PNT) services and space manufacturing, the number of satellite launches is expected to increase.
As satellite launches increase, concerns are also growing. The risk of collisions has increased as the number of satellites in orbit rises. The collision risk from space debris, such as defunct satellites or rocket parts left in space during the launch process, has soared. The UN reports that the problem of space debris hinders the sustainable use of space and has urged member states to consider solutions to this issue.
The problem is that if greenhouse gases continue to be emitted into the atmosphere, the natural processing of space debris abandoned in low Earth orbit will become increasingly difficult. Defunct satellites continue to orbit Earth for years or even decades, gradually losing speed due to friction as they collide with the thin layers of the upper atmosphere and getting pulled by Earth’s gravity, ultimately burning up in the atmosphere.
According to the U.S. Naval Research Laboratory and NASA, the thermosphere (at an altitude of 85-600 km) that makes up the upper atmosphere of Earth regularly contracts and expands in response to solar activity. As the thermosphere undergoes contraction and expansion, the density in the atmosphere changes, potentially impacting satellite collisions, scientists report. Recently, it has also been confirmed that as the amount of greenhouse gases in the atmosphere increases, the thermosphere that constitutes the upper atmosphere, along with the mesosphere (at an altitude of 50-85 km), decreases similarly to solar activity.
Carbon dioxide, one of the greenhouse gases, has the property of absorbing and re-emitting infrared (IR) radiation in the atmosphere. Greenhouse gases trap heat emitted from Earth's surface in the troposphere, causing a warming effect, while in the stratosphere, mesosphere, and thermosphere, the infrared radiation from greenhouse gases offsets solar energy absorption, playing a crucial role in Earth's thermal balance. In the upper thermosphere, conduction occurs at altitudes between 90-135 km, where an increase in carbon dioxide concentration cools the upper atmosphere, causing the thermosphere to contract.
As the upper atmosphere contracts, the density of the space in low Earth orbit decreases, and the resistance with the atmosphere also reduces. With less resistance, the time space debris remains in orbit increases. When the mass density in low Earth orbit decreases, space debris accumulates in the orbit more quickly.
The MIT research team estimated the number of satellites that can safely operate in orbit around Earth by 2100 using various greenhouse gas emission scenarios. They estimated the ideal distribution of orbital objects observed in several emission scenarios and the deviation from the ideal distribution. It turned out that in the scenario with the highest greenhouse gas emissions, the number of satellites deviating from their orbits due to atmospheric friction significantly decreased compared to scenarios with lower emissions.
In the scenario corresponding to a high-emission share socio-economic pathway (SSP5-8.5), where greenhouse gas emissions increase compared to now, they confirmed that the capacity for operating satellites between 200-1000 km will decrease to 50-66% by 2100. This means that around 25 million to 40 million satellites will miss their launch opportunities because they cannot find safe orbits. This high-emission scenario corresponds to a situation where 'rapid industrial technological development is prioritized, fossil fuel usage increases, and indiscriminate urban development expands.' The concentration of carbon dioxide in the atmosphere, currently at 420 ppm, is assumed to rise to 1,089 ppm by 2100.
Starlink, which provides low Earth orbit satellite services, currently launches between 20 and 49 low Earth orbit communication satellites at a time. Following the British competitor OneWeb, China is also beginning to build a constellation satellite service, which is expected to significantly increase the number of satellite launches. On the 5th, Goldman Sachs, a major U.S. investment bank, projected that over the next five years, 70,000 satellites will be launched into low Earth orbit. As space debris increasingly fills Earth’s orbital space, the probability of collisions with rockets or existing satellites rises. Space debris is expected to continue to increase for the time being, thereby reducing the orbits available for launching new satellites. This means there will be fewer opportunities to provide new services such as low Earth orbit satellite communications, satellite imagery, and space manufacturing.
As concerns grow that space debris prevents continuous space development, measures are also being developed. There is a focus on technology that captures debris floating in low Earth orbit and then either drops it back to Earth or allows satellites to autonomously exit their orbits. Companies such as Astroscale from Japan, ClearSpace, and Catalyst Space Technologies are developing technologies to remove space debris from orbit. However, this research is noteworthy as it suggests that environmental constraints arising from increased greenhouse gases may exceed these efforts. The researchers noted, "Mitigating greenhouse gas emissions has emerged as a critical task in preserving humanity's accessibility to both Earth's climate and space."
References
Nature Sustainability (2025), DOI: https://doi.org/10.1038/s41893-025-01512-0
JGR Space Physics (2015), DOI: https://doi.org/10.1002/2015JA021047