Scientists puzzled by atmosphere shrinkage

WASHINGTON, July 17 (UPI) -- An unprecedented shrinkage of an upper layer of Earth's atmosphere has U.S. scientists scrambling to find an explanation, NASA says.

The thermosphere, which blocks harmful ultraviolet rays, expands and contracts regularly due to the sun's activities and with increases in atmospheric carbon dioxide, but these two factors cannot account for the recent extraordinary contraction, CNN reported Saturday.

"This is the biggest contraction of the thermosphere in at least 43 years," John Emmert of the Naval Research Lab said in a National Aeronautics and Space Administration report.

The thermosphere extends from 55 miles to 370 miles above the Earth's surface, close to where the atmosphere ends and space begins.

That's the realm of meteors, auroras, space shuttles and the international space station, CNN reported.

Though still puzzled, scientists say the contraction of the thermosphere is unlikely to have a direct effect on our daily lives.

"It's not going to affect the weather, or you won't be able to tell that this is going on by looking at the sky," Stanley Solomon, a senior scientist with the National Center for Atmospheric Research, said.

"It's not going to look any darker," he said.

But the contraction can mean less drag on satellites and space junk orbiting at those levels.

"Debris that's up there stays up longer. The amount of orbital debris is a concern for space navigation. There is concern that space debris is building up," Emmert said.