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An upper layer of Earth's atmosphere recently shrank so much that researchers are at a loss to adequately explain it, NASA said on Thursday.

The thermosphere, which blocks harmful ultraviolet rays, expands and contracts regularly due to the sun's activities. As carbon dioxide increases, it has a cooling effect at such high altitudes, which also contributes to the contraction.

But even these two factors aren't fully explaining the extraordinary contraction which, though unlikely to affect the weather, can affect the movement of satellites, researchers said.

"This is the biggest contraction of the thermosphere in at least 43 years," John Emmert of the Naval Research Lab was quoted as saying in NASA news report.

Emmert is the lead author of a paper announcing the finding in the June 19 issue of the journal Geophysical Research Letters.

"We cannot explain the abnormally low densities, which are about 30 percent lower" than from previous contractions, Emmert told CNN.com.

The thermosphere interacts strongly with the sun and hence is greatly influenced by the sun's solar activity, which occurs in cycles.

Still, the collapse of the thermosphere was bigger than the sun's activity alone can explain.

Emmert suggests that the increasing amounts of carbon dioxide making its way into the upper atmosphere might have played a role in the anomaly.

Carbon dioxide acts as a coolant in the upper atmosphere, unlike in the lower atmosphere, shedding heat via infrared radiation. As carbon dioxide levels build up on Earth, it makes its way into the upper levels and magnifies the cooling action of the solar minimum, Emmert said.

"It could be that we're underestimating the effects [of carbon dioxide] somehow. It could be because there were some physics that we're missing in the region of the atmosphere below the thermosphere, which quickly affects the thermosphere," he said.

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Hippie Operative Nikovich Nikita Nicovna Talibani,
signing off

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Human made compounds (particularly CFCs) that get caught over Antarctica in the winter months greatly accelerate the natural decay of ozone over Antarctica.

Technically it's never an outright "hole" but what people are referring to is there tends to naturally be an extreme drop in concentration.

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Hippie Operative Nikovich Nikita Nicovna Talibani,
signing off