Cool Sun bursts with magnetic energy

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FIELDS of magnetic energy resembling "loops" are released from the Sun's surface (above) - the sort of event that can trigger a solar flare, disrupting communications satellites and power systems here on Earth.

Known as a "magnetic reconnection", the loops were thrown out from the surface - where the red areas indicate temperatures of 1.1mC, and even the "cool" blue areas are at 200,000C - into space, and then curved back together. The effect of their interplay is to release huge amounts of energy, like a twisted rubber band unwinding or breaking, according to scientists at the US space agency Nasa, who captured the picture.

The superheated gas that fuels our star is constantly being ejected by processes within the body of the Sun which scientists are still struggling to understand. "Our mission is to understand in great detail how energy is transported from the solar surface into the outer atmosphere," said Dr Alan Title, head of Stanford Lockheed Institute in Palo Alto, California.

Normally, the surface of the Sun is relatively cool - about 5,000C - yet its upper atmosphere, the corona, has temperatures of 1.6mC. The spacecraft being used to study this energy transfer is called Trace. Launched in April, it will be able to record changes in solar activity in greater detail, both in time and distance.

That should help, said Dr Title, because past systems had to average data over long periods: "This made it difficult to get at the fundamental physics." He added: "Trace has given us many surprises already. We found that even large areas of the Sun, some more than 96,000 kilometres (60,000 miles) can heat up or cool down significantly, and thus appear and disappear on our instruments in just a few minutes."

Photograph: Dr Alan Title

Stanford Lockheed Institute for Space Research and Nasa