Sun's big bursts have small-time origins

NASA’s Solar Dynamics Observatory (SDO) has made good on its promise of getting down to the fine details that drive activity on the Sun, after researchers revealed new findings that show how small scale disturbances can have big impacts.

A prominence beginning to erupt on the Sun’s limb, caused by a cascade of rippling Alfven waves sparked by small-scale flares. Image: NASA/SDO/AIA.

One of SDO’s principal instruments is the Atmospheric Imaging Assembly (AIA), which is able to image the entire solar disc in high-resolution in one-shot, capturing how activity on one part of the Sun can cascade across and affect other regions. “We are in essence watching the butterfly effect on the Sun,” said W Dean Pesnell, SDO’s Principal Scientist from the Goddard Space Flight Center, at this week’s 216th meeting of the American Astronomical Society in Miami, Florida. Pesnell was referring to the analogy in chaos theory that describes how the smallest events can sometimes have the biggest impacts.

The AIA watched as small flares generated by magnetic fields emerging onto the photosphere (the Sun’s ‘surface’) created magnetic Alfven waves in which solar plasma becomes ‘frozen’ to a magnetic loop by electrical currents and ripples across the Sun. “These waves affect local regions perhaps five to ten times their diameter, which then affect their neighbours, and so on,” says the AIA Principal Investigator, Alan Title from Lockheed Martin, who built the instrument with cameras put together in the UK by the Rutherford Appleton Laboratory and technology company e2v. “AIA has shown for the first time that these cascades exist.”

The Alfven waves cascade across the solar disc at speeds ranging between hundreds to thousands of kilometres per second, depending upon the amount of mass that they are rippling through. By watching these ripples spread to larger areas, potentially instigating prominences and coronal mass ejections, solar physicists will be able to measure the properties belonging to the Sun’s magnetic field and gases in the Sun’s million-degree hot outer atmosphere, the corona. These observations are vital to understanding what is causing the corona to become so hot, and with SDO producing as much data in a day as its older cousin, the TRACE spacecraft, generated in five years, we now have the best chance we’ve ever had of unlocking the Sun’s secrets.

To learn more about the Sun, look out for the July issue of Astronomy Now, on sale in newsagents on 17 June.