High in the upper atmosphere, something strange is happening… Earth’s atmospheric shell is actually contracting. This contraction is noticeable enough that it is actually producing a measurable reduction in the atmospheric drag on satellites and space junk in Low Earth Orbit.

Firstly, a quick reality check on Earth’s atmosphere. Many of our satellites operating in LEO do so in the Thermosphere (and even as low as the Ionosphere). Both layers together stretch between 37 and 430 miles (60 and 690 kilometers) above the Earth’s surface until it tapers off into outer space in a region called the Exosphere. The density is so low satellites are able to orbit with minimal drag, but over time, they are slowly descending towards the Earth due to this drag. They must occasionally fire their thrusters to raise their orbits to prevent themselves from crashing.

As I trust you all know, when a gas is heated, it expands. Likewise, as a gas is cooled, it contracts. It might sound a little counter intuitive that global warming would actually cause a contraction of the upper atmosphere, but bear with me a moment.

Again, as I trust you know, carbon dioxide (CO2) is a green house gas and, in the lower layers of the atmosphere, it traps heat from the Sun. However, in the upper layers of the atmosphere, on the edge of space, CO2 actually causes cooling. Here, CO2 is too thin to recapture the Sun’s heat; instead, CO2 collides with oxygen atoms causing the CO2 to get excited and radiate heat. The more CO2 radiating heat into space, the cooler the upper atmosphere gets, which leads to the contraction of upper layers of Earth’s atmosphere and thus reduces drag on satellites – that was a mouthful.

As ultraviolet light from the Sun strikes the carbon dioxide, the CO2 breaks apart into carbon monoxide and oxygen. Scientists have named the concentration of CO2 and carbon monoxide COx. A recent study taken by the Canadian SCISAT-1 satellite shows the COx level has risen significantly over the last decade. Current estimates place this increase at about 10 parts per million faster than our previous models predict.

Scientists believe this sharp increase is due to a larger than predicted amount of mixing between Earth’s atmospheric levels. Scientists are now trying to understand why the CO2 levels are much larger than expected to help improve their atmospheric models.

As far as the satellites are concerned, they are safe. With proper adjustments they will maintain their stable orbits and will have to readjust less frequently due to the reducing drag from the atmosphere.

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