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Where does space begin?

Edge of Space pinpointed by University of Calgary scientists

Scientists at the University of Calgary have created a new instrument able to track the transition between the relatively gentle winds of Earth's atmosphere and the more violent flows of charged particles in space - flows that can reach speeds well over 1000 km/hr. And they have accomplished this in unprecedented detail.

The instrument-called the Supra-Thermal Ion Imager-was launched aboard the JOULE-II rocket on January 19, 2007. It travelled to an altitude of about 200 kilometres above sea level and collected data for the five minutes it was moving through the "edge of space."

Data received from the Supra-Thermal Ion Imager helped confirm that space begins 118 km above Earth. The results were recently published in the Journal of Geophysical Research.

The ability to gather data in that area is significant because it's very difficult to make measurements in this region, which is too high for balloons and too low for satellites. "It's only the second time that direct measurements of charged particle flows have been made in this region, and the first time all the ingredients-such as the upper atmospheric winds-have been included," says David Knudsen, associate professor in the Department of Physics and Astronomy at the University of Calgary.

"When you drag a heavy object over a surface, the interface becomes hot. In JOULE-II we were able to measure directly two regions being dragged past each other, one being the ionosphere-being driven by flows in space-and the other the earth's atmosphere," says Knudsen, who also is the head of the Space Physics Division of the Institute for Space Imaging Sciences.

"The results have given us a closer look at space, which is a benefit to pure research in space science," Knudsen says. "But it also allows us to calculate energy flows into the Earth's atmosphere that ultimately may be able to help us understand the interaction between space and our environment. That could mean a greater understanding of the link between sunspots and the warming and cooling of the Earth's climate as well as how space weather impacts satellites, communications, navigation, and power systems."

The University of Calgary and COM DEV, an Ontario-based global designer and manufacturer of space hardware, have updated the design of the Supra-Thermal Ion Imager and are preparing three more advanced instruments for flight on the European Space Agency's Swarm satellite mission, set to launch late in 2010 and to collect data for four years.

The Canadian Space Agency supported the development of the Supra-Thermal Ion Imager on JOULE-II. Knudsen and his former PhD student Laureline Sangalli are the lead authors of the paper, entitled, "Rocket-based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere." Co-authors include: JOULE-II lead scientist Miguel Larsen of Clemson University, Robert Pfaff and Douglas Rowland of NASA Goddard Space Flight Center and T. Zhan of Conseco Inc.