Solar spectacular: During a total solar eclipse the Moon passes in front of the Sun, blocking out the most intense solar light and allowing us to view the Sun's outer atmosphere, or corona, from Earth. The Sun's light can be seen streaming through the immense magnetic structures that thread through the corona and out into space.

Credit: Luc Viatour GFDL/CC

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SYDNEY: Immense gas ‘fountains’ that erupt continuously on the surface of the Sun are powered by changes in pressure in the solar magnetic field, British scientists say.

The findings are based on images of the Sun’s corona taken by the Japanese and international Hinode spacecraft, launched in October 2006. Researchers used these images, computer modelling and spacecraft data to examine the Sun’s surface in great detail.

The Sun’s atmosphere - the corona - can reach temperatures of several million degrees Celsius. According to the researchers, who were led by Michelle Murray from the Mullard Space Science Laboratory (MSSL) at University College London, fountains or ejections into the corona occur when sudden changes in pressure are caused by continual rearrangements of the Sun’s magnetic field.

Under pressure

These changes in the solar magnetic field result in looping cycles of increasing pressure (forcing the jets up) and decreasing pressure (allowing the jets to collapse). The resulting eruptions are on a smaller scale than solar flares but may still be tens of thousands of kilometres across, said the researchers, who presented their results at the Royal Astronomical Society National Astronomy Meeting in Belfast, Ireland, yesterday.

Hinode was launched specifically to study solar eruptions and changes in the Sun’s magnetic field, and carries on board the Extreme Ultraviolet Imaging Spectrometer (EIS), which observed the Sun's fountains in “unprecedented detail” according to team member and MSSL postgraduate student Deb Baker. The spacecraft also carries a vector magnetograph capable of looking at the components of the Sun’s magnetic field and an X-ray device that can ‘see’ into the solar corona.

“[The EIS] has enabled us to narrow down the fountains' origins for the first time. We have also been able to find what drives the fountains by using computer experiments to replicate solar conditions," Baker said.

Murray added that new magnetic fields are constantly emerging across the whole of the solar surface and that the team’s results can explain a whole multitude of the fountains that have been observed with Hinode.

Bubbling geyser

Astrophysicist John Humble from the University of Tasmania and Australian Antarctic Division compares the eruptions to bubbling mud pools that occasionally erupt in geysers on Earth. “The outer layers of the Sun are in continuous agitation”, he said, adding that while the results are not surprising, it is a major extension of current knowledge about the processes driving these eruptions.

University of Sydney astrophysicist Mike Wheatland said that while the theory (that rearrangements of the Sun’s magnetic field can create solar flares) is not new, the research is interesting and shows these processes operating at a smaller scale and in more detail.

Hinode, which was developed by the Japanese Aerospace Exploration Agency in conjunction with NASA, the Science and Technology Facilities Council, and the European Space Agency, is part way through a three-year mission to study the solar atmosphere and the mechanisms that drive solar eruptions.