Magazine article Science News

Untangling the Solar Corona's Structure

Magazine article Science News

Untangling the Solar Corona's Structure

Article excerpt

The cauldron of gases at the sun's visible surface measures 6,000 kelvins. But venture a few thousand kilometers higher, and temperatures typically zoom into the millions of kelvins. Welcome to the solar corona, where vast, arching magnetic fields hold sway and bursts of radiation can occasionally exceed the temperature at the sun's very core.

Scientists have tried for more than half a century to explain how the corona retains its heat. But they lacked the observational tools to discriminate clearly among various models. Examining new X-ray images obtained by the Japanese Yohkoh satellite, however, two researchers argue that coronal heat comes from energy released when tangles of magnetic fields unwind.

James A. Klimchuk of the Naval Research Laboratory in Washington, D.C., and Lisa J. Porter of the Massachusetts Institute of Technology report in the Sept. 14 Nature their analysis of Yohkoh images of 47 loops of coronal gas sculpted by the arching magnetic fields.

Klimchuk and Porter note that in recent years, three models have taken center stage in the effort to explain the corona's high temperatures. In one model, wavelike motions that originate at the sun's turbulent surface propagate along magnetic field lines into the corona, where they act as a steady source of energy.

The other two models rely on energy generated when the corona's magnetic fields--either singly or in groups--twist or tangle. The twisting arises because these arching fields begin and end at "footpoints" in the sun's visible surface. The turbulence at the surface causes the footpoints to wander, tangling the magnetic fields.

In one of these models, individual fields become so twisted that they eventually snap like rubber bands, unleashing energy fields. In the other, neighboring fields wind around each other, creating what the researchers call "a bowl of tangled spaghetti. …

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