Satellites in a low Earth orbit may remain aloft for longer as a result of global warming. Unfortunately, the same applies to space junk.
Researchers predicted in 1989 that rising greenhouse gas concentrations in the atmosphere would affect the climate in the upper reaches of the atmosphere. Now, Jan Laštovička, at the Institute of Atmospheric Physics in Prague, Czech Republic, and his colleagues say that there is mounting evidence for this. Their review of recent findings appears in Science.
Rising levels of carbon dioxide in the lower atmosphere isare causing it to warm due to the greenhouse effect. Over the past three decades, the temperature at the Earth’s surface has increased by up to 0.4 °C.
This heat is travelling upwardrisess to the upper atmosphere where it causes CO2 there to emit infrared radiation. Because the atmosphere is very thin at these altitudes, only some of the radiation is re-absorbed by other CO2 molecules.
The net result is a cooling of the upper atmosphere, which the researchers say has been confirmed by several measurements over the past decade (see, for example, Orbital tracking reveals thinning upper atmosphere).
Cooling and contracting
Cooling gases contract and the researchers say that the contractionwhen this happens in the upper stratosphere ,( around 40 km above the Earth,) is causing the higher levels of the atmosphere, (around 80 km and above,) to become less dense.
This, says Laštovička, will affect the life expectancy and trajectory of satellites orbiting the Earth. On the upside, less drag on satellites will give them a longer lease ofn life, but on the downside, space junk will take longer to fall towards Earth and burn up.
“Perhaps fewer and smaller adjustments to the orbits of low Earth satellites, such as the International Space Station, would be needed to keep them in their assigned orbits,” says Richard Langley of the University of New Brunswick in Canada.
Another of Laštovička’s concerns is that a thinner upper atmosphere will offer satellite solar panels less protection from high-energy particles which that could degrade the satellites’ primary power source.