Comment »Posted on Friday 10 April 2009 at 6:17 pm by Jacob Aron
In Space & Astronomy

We’ve had a few stories on Just A Theory about people sending objects into space using impressively cheap materials, and each time I’ve come away wondering just high high about the planet we count as “space”. Now, scientists at the University of Calgary in Canada can provide an answer.

Two years ago their research team created an instrument for a NASA mission designed to monitor the difference between the winds of Earth’s atmosphere and the flow of charged particles in space. These flows can reach speeds of over 1000 km/hr, and they mark they very edge of the atmosphere – the gateway to space.

Data from that instrument has now been analysed, and results published this week in the Journal of Geophysical Research confirm that space begins 118km above the Earth’s surface. I can’t access the paper, “Rocket‐based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere”, but it’s there if you want it.

Called the Supra-Thermal Ion Imager, the measuring instrument was launched aboard the JOULE-II rocket on 19th January 2007. Costing $422,000 to develop, it collected data for just five minutes as the rocket passed through the edge of space. An expensive way to find out where out planetary backyard ends and the rest of the universe begins, but carrying out such a measurement is actually quite tricky.

The region containing the edge of space is too high for balloons, but too low for satellites. This experiment marks the first time comprehensive data has been gathered, says one of the paper’s lead authors, David Knudsen:

“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.”

Knudsen is an associate professor in the Department of Physics and Astronomy at the University of Calgary, and explained that the Supra-Thermal Ion Imager measured the heat released by frictional forces rubbing on the atmosphere:

“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.”

Besides the simple satisfaction of knowing, is there any reason to find the edge of space? Yes, says Knudsen. It could further our understanding of the Earth’s atmosphere and help in the fight against climate change.

“The results have given us a closer look at space, which is a benefit to pure research in space science,

“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.”

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