THE CANADIAN PRESS
CALGARY - The answer to the question of exactly where Earth's atmosphere gives way to the bleakness of beyond is blowing in the winds of space, suggests research from the University of Calgary.
New data confirms that, by one definition, the boundary is 118 kilometres above the Earth. That's about the same distance as the drive between Calgary and Banff or Toronto and Waterloo, Ont.
Astronomy professor David Knudsen says a specialized instrument designed by the school was attached to a NASA rocket shot through the windy area where Earth's atmosphere meets space.
The university's specialized Supra-Thermal Ion Imager recorded detailed information about the extreme heat produced by the friction between Earth's gentle winds and the dizzying blasts of space.
Solar wind, made up of charged particles blowing away from the sun, can be thousands of kilometres an hour, he said.
"If you think of these two regions - atmospheric winds and the space winds - being two different flows, then right at the boundary there's friction where they slip across each other, and it actually heats up that region," Knudsen said.
"It's an important source of heat and energy for the upper atmosphere.
"The boundary that we were reporting is the halfway point, really, between very fast winds in space and slower winds in the upper atmosphere."
It's been hard to do research on that boundary because it's lower than the altitude at which satellites orbit, but higher than research balloons can fly.
The limit of 118 kilometres had been suggested by computer models and research done from the ground, but little detailed information had been gleaned from the region itself.
Knudsen stressed that it's not easy to put an exact figure on where outer space begins.
While they came up with 118 kilometres, those working with space shuttles consider it the place where the shuttles switch from thrusters to aerodynamic flaps - about 122 kilometres above sea level.
Other people have put it closer to 110 kilometres, said Jaymie Matthews, an astrophysics professor at the University of British Columbia. He was not involved in the University of Calgary research.
"It all depends on what physical characteristics of the atmosphere are important to you," said Matthews, adding most people think of space as a vacuum, but it's hard to say at what pressure that technically begins.
"It's all very gradual."
19:37ET 13-04-09
