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WASHINGTON (AFP) – The upper reaches of Earth's atmosphere are unexpectedly shrinking and cooling due to lower ultraviolet radiation from the sun, US scientists said Thursday. The sun's energy output dropped to unusually low levels from 2007 to 2009, a significantly long spell with virtually no sunspots or solar storms, according to scientists from the National Center for Atmospheric Research in Boulder, Colorado. During that period, the thermosphere, whose altitude ranges from about 55 to 300 miles (90 to 500 kilometers), shrank and contracted from the sharp drop in ultraviolet radiation, said the study published in the American Geophysical Union's...

(CNN) -- 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.

An upper layer of Earth's atmosphere recently collapsed in an unexpectedly large contraction, the sheer size of which has scientists scratching their heads, NASA announced Thursday. The layer of gas – called the thermosphere – is now rebounding again. This type of collapse is not rare, but its magnitude shocked scientists. "This is the biggest contraction of the thermosphere in at least 43 years," said John Emmert of the Naval Research Lab, lead author of a paper announcing the finding in the June 19 issue of the journal Geophysical Research Letters. "It's a Space Age record." The collapse occurred during...