COLUMBIA, MD. (June 19, 2003) — For scientists who study solar flares, the
hottest spots in the solar system just got substantially hotter.

The hottest spots in solar flares reach temperatures as much as 20 million
degrees Fahrenheit hotter than solar physicists had previously believed,
topping out at more than 80 million degrees Fahrenheit. And from about 5
million degrees just before a flare, in less than a minute temperatures in
the sun’s atmosphere can warm by more than 75 million degrees.

Using data gathered by NASA’s Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI), scientists from The University of Alabama in Huntsville
(UAH), the University of Glasgow and the University of California at
Berkeley were able to isolate and measure sources of the most powerful
X-rays emitted by a solar flare on July 23, 2002.

“Previously the best we could do was look at an average temperature for the
entire flare,” said Dr. Gordon Emslie, who is scheduled to present the
findings today at a meeting of the American Astronomical Society’s Solar
Physics Division in Columbia, MD. “With RHESSI we get an incredible amount
of data. One of the things we can do with that is look at the hottest point
sources within a flare.

“We have been able to take a picture of the hot spot and the data from that
‘ups the ante’ considerably.”

RHESSI images of the flare show a bright “blob” suspended 7,000 miles above
the sun. Below it are three hot spots on the solar surface.

“This suspended blob is extremely hot,” said Emslie, a physics professor at
UAH. “That’s where the temperature hit 45 million Kelvin — about
80,000,000 degrees Fahrenheit, give or take a million. We think the other
three bright spots are where electrons from that hot blob are being slammed
into the surface. And when they hit they release energy in the form of
X rays.”

These findings will force Emslie and other solar physics theorists to
re-examine the theories they have developed to explain the most massive
explosions in the solar system.

“Now we have to stop talking about 30 million Kelvin and start thinking
about 40 or 45 million Kelvin,” he said. “That represents a bigger
concentration of energy, which has to be explained in our theories and our
models.”

The power released by a large solar flare – such as the one on June 23,
2002 – would be measured in the billions of trillions of kilowatts. If
certain types of flares erupt on the side of the sun facing Earth, waves of
electromagnetic energy can disrupt telecommunications, black out power
systems, and play havoc with satellites. It might even endanger astronauts
working outside a space shuttle or space station.

Solar activity has caused power outages in Canada, and blurred TV and
telephone signals bounced off satellites. Magnetic storms cause power
outages when waves of electromagnetic particles from the sun hit power lines
and electrical transformers. Just as electrical power is generated on the
sun by the interaction of magnetic fields, electromagnetic fields from the
sun induce electrical current in transformers and power lines on Earth.
Those extra surges of power can trip circuit breakers and shut down power
systems.

“If we’re ever going to be able to predict these things, we have to
understand them better,” said Emslie. “And RHESSI is helping us do that.”