Collapse in Earth's Upper Atmosphere Stumps Researchers

Something very odd is taking place in the earth's upper atmosphere that has scientists baffled.

The "thermosphere," a rarefied layer of gas at the boundary line between the atmosphere and space that stars about 50 miles above the Earth, recently collapsed and now is rebounding again.

According to John Emmert of the Naval Research Lab, this constitutes "the biggest contraction of the thermosphere in at least 43 years." Emmert, lead author of a paper announcing the findings in the journal Geophysical Research Letters, terms this "a Space Age record."

In a note put out by NASA announcing the finding, the researchers said they were stumped to explain the extent of the collapse, which was two to three times greater than low solar activity could explain. They noted that the thermosphere can be expected to cool and contract when solar activity is low, but not like this.

Solar radiation makes first contact with the earth when it enters the thermosphere, which acts as a barrier against extreme ultraviolet photons from the sun. This constant solar pounding can warm up the thermosphere to temperatures as high as 1,727 Celsius when solar activity is high. But of late - in 2008 and 2009, specifically, it's been just the opposite with few solar flares or solar ultraviolet radiation.

Emmert said that one possible explanation is the presence of carbon dioxide, which would act as a coolant as it gets into the thermosphere. But even then, he said, the the numbers don't quite add up.

"Even when we take CO2 into account using our best understanding of how it operates as a coolant, we cannot fully explain the thermosphere's collapse," he said.