Imagine there’s a super-rich alien living on a nearby planet. It runs a business that involves making and launching hi-tech satellites (far better than those made by NASA). While looking for new opportunities to expand its business, the alien came across Earth, the only other known planet where thousands of satellite launches happen every year.

His company has a superior technology, can provide services at a lower cost, and there’s no shortage of clients on Earth. However, the alien still drops the plan. Can you guess why? No, not because they watched Independence Day, but rather because, unlike most business people on Earth, this alien listens to what the science says.

A new study suggests that Earth’s orbit could become unsustainable for satellites in the long term due to rising greenhouse gas emissions, and it isn’t the only one saying it. 

Researchers at MIT found that greenhouse gases are causing Earth’s upper atmosphere to shrink. Gradually, this will lead to more and frequent satellite collisions, limiting the number of satellites that can safely operate there.

Understanding the thermosphere

The International Space Station technically isn’t in space. It’s located in the thermosphere, the layer of the atmosphere at 85 to 600 km (~50 to 375 miles) above the Earth’s surface. This is also where most satellites orbit our planet. 

The thickness of this layer is influenced by the solar cycle that repeats every 11 years. So, when solar activity increases, the Sun emits more radiation, causing the thermosphere to expand. During periods of lower solar activity, the thermosphere contracts.

However, scientists have found evidence suggesting that solar activity isn’t the only thing affecting the thermosphere. They discovered that greenhouse emissions can disturb its natural contraction and expansion.

“In the last decade, scientists have been able to measure changes in drag on satellites, which has provided some evidence that the thermosphere is contracting in response to something more than the sun’s natural, 11-year cycle,” the MIT team notes.

The authors ran some simulations to check the extent to which greenhouse gas emissions influence the thermosphere and its satellite carrying capacity.   

More greenhouse emissions, less carrying capacity

Under normal conditions, Earth’s upper atmosphere creates a small amount of drag that gradually slows down old satellites and space debris. This drag pulls them into lower altitudes, where they eventually burn up due to friction with air molecules. This natural process helps clear space junk from orbit.

However, when greenhouse gases reach the thermosphere, the air there becomes even thinner, reducing this natural drag.

“At the same time, there’s been a massive increase in the number of satellites launched, especially for delivering broadband internet from space. 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,” William Parker, lead researcher and a graduate student at MIT, said.

Through the simulations, the researchers compared the satellite carrying capacity of thermosphere when greenhouse emissions remain at levels reported in the year 2000 to scenarios where these emissions continued to rise. 

The study highlights a serious problem that has been long overlooked. It suggests that if emissions continue to rise at this rate, Earth’s orbit may not be able to accommodate even half as many satellites by 2100 as it does today.

“Modelled CO2 emissions scenarios from years 2000–2100 indicate a potential 50–66% reduction in satellite carrying capacity between the altitudes of 200 and 1,000 km,” the study authors note.

These findings add another danger of the rising greenhouse gas emissions. Hopefully, they will encourage space agencies and companies to adopt a more responsible approach to satellite launches and space junk management.

The study is published in the journal Nature Sustainability.