U of T professor contributes to ground-breaking discovery of plasma tubes around Earth

Some of you may remember this popular middle school science experiment: tapping iron filings on a sheet of paper above a bar magnet to see how the magnet arranged the filings into circular patterns along the magnetic field lines. A group of astronomers recently proved that the Earth’s magnetic field causes giant invisible plasma tubes to embed in the Earth’s atmosphere according to a similar principle..

“For over 60 years, scientists believed these structures existed, but by imaging them for the first time, we’ve provided visual evidence that they are really there,” said student researcher Cleo Loi of the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO).

Loi has recently published this award-winning research in Geophysical Research Letters. University of Toronto’s Dunlap Institute director and former director of CAASTRO, Prof. Bryan Gaensler, is among the team of astronomers who made the discovery.

The tubes are intricate, multilayered ducts that form as the sun ionizes the atmosphere, which then align with the earth’s magnetic field lines.

“We saw a striking pattern in the sky where stripes of high-density plasma neatly alternated with stripes of low-density plasma,” recalls, Loi. “This pattern drifted slowly and aligned beautifully with the Earth’s magnetic field lines, like aurorae.”

“The discovery of the structures is important because they cause unwanted signal distortions that could, as one example, affect our civilian and military satellite-based navigation systems. So we need to understand them.”

The team used the Murchison Widefield Array (MWA), a low frequency radio telescope located in the outback of Western Australia. It was built as part of a joint effort by an international consortium of universities, and can make astronomical observations ranging from as near as the atmosphere to as far as the celestial bodies of the early universe.

The telescope has 128 antenna tiles expanding on nine square metres of land — and this wide area coverage is cardinal. It allowed them to divide the tiles into east and west halves, acting as ‘eyes’ that are able to perceive depth as well as observe large parts of the sky. Not only did they prove the existence of the tubes, but thanks to the MWA’s rapid snapshot capabilities, they were also able to film a three dimensional movie of the plasma tubes moving and shifting in the sky.

“We measured their position to be about 600 km above the ground, in the upper ionosphere, and they appear to be continuing upwards into the plasmasphere,” says Loi.

Professor Gaesner indicates that there is much more to be discovered. “This work highlights the new frontier that the MWA is opening up. By operating at low radio frequencies and covering such an enormous field of view, we can study subtle and complicated processes that we had only ever caught fleeting glimpses of previously.”

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