Space Is Closer Than You Think

Jan. 7, 2008 -- Earthlings have had an over-inflated view of how far the planet's atmosphere extends into space. Turns out, the ionosphere, the layer of electrically charged particles that comprises the outer atmosphere, is thinner than expected -- and cooler.

Understanding the shape and size of the ionosphere is an important first step in figuring out how particularly dense regions within it may distort radio, radar and navigation signals. Such distortions can make communications and satellite-based systems less reliable.

"In order to predict how severe those distortions will be, it's necessary to know how big those structures in the ionosphere are and where they exist," Roderick Heelis, with the Space Sciences Center at the University of Texas in Dallas, told Discovery News.

Hellis and his colleagues have been using a suite of NASA instruments called CINDI, which fly on the U.S. Air Force Communication/Navigation Outage Forecast System (C/NOFS) satellite between 250 miles and 530 miles around the planet's equator.

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The researchers never expected to encounter the fringe of Earth's ionosphere at those altitudes, but that is exactly what happened during the summer of 2008, a time when the solar activity was unusually quiescent.

"It was a real fortuitous combination of low solar activity and the satellite's [range]," Hellis said. "We didn't expect to be able to look at the top of the ionosphere in all places."

Computer models based on previous research had predicted the ionosphere to be about 370 miles above Earth at night and about 620 miles up during the day -- the variation due to temperature and other factors.

Instead, the CINDI team discovered that the transition between the ionosphere and space was about 250 miles above Earth at night and about 500 miles up during the day.