Tuesday March 9 7:28 PM ET

Sun's Fiery S-Shapes Foretell Massive Solar Blasts

By Deborah Zabarenko

WASHINGTON (Reuters) - Fiery S-shapes on the Sun's surface can help predict when potentially dangerous and disruptive blasts of electrically charged gas will come hurtling toward Earth, scientists said Tuesday.

Such massive solar explosions pack the force of billions of nuclear blasts and can knock out power grids, damage satellites and scramble communications networks, so forecasting them is becoming increasingly important.

Until now, scientists have only been able to tell that one of these big solar blasts had already occurred, which still gave Earth two to three days to prepare while the blast traveled toward the planet.

But the discovery of the telltale S shape means forecasters can detect the blast even before it happens, giving Earth up to five or six days to get ready.

The S-shapes, called sigmoids, were glimpsed by the Japanese Yohkoh spacecraft and explained at a briefing at NASA headquarters Tuesday.

``The sigmoid is like a loaded gun that we now know has a high probability of going off,'' said Aphonse Sterling, of the Institute of Space and Astronautical Science (ISAS) of Japan.

``We have found a strong correlation between an S-shaped pattern on the Sun ... and the likelihood that an ejection will occur from that region within days,'' Sterling said.

These massive blasts, which scientists call coronal mass ejections (CMEs), are likely to be more frequent in 2000 as the Sun moves into the most active year of its 11-year cycle of activity.

CMEs are the largest explosions in the solar system, hurling up to 10 billion tons of gas into space at speeds of 1 billion to 2 billion miles an hour (1.6 billion to 3.2 billion km an hour), several times a day. Not every CME is aimed at Earth.

Sigmoids are ``a very twisted, slinky-like structure'' related to the Sun's underlying magnetic field, according to Sarah Gibson of the University of Cambridge, England, who also participated in the briefing.

Not every CME is presaged by a sigmoid, the scientists said, but most sigmoids signal very large CMEs.

The Yohkoh images show an S-shape as the precursor to a CME and an arch-shape as the sign that the blast has already occurred, the scientists said.

The National Aeronautics and Space Administration is planning a mission called STEREO, with two spacecraft that will make three-dimensional images of CMEs and other solar structures.