A New Kind of Solar Storm

http://science.nasa.gov/headlines/y2...n_newstorm.htm

A New Kind of Solar Storm
NASA Science News
June 10, 2005

January 2005 was a stormy month--in space. With little
warning, a giant spot materialized on the sun and started exploding.
Between January 15th and 19th, sunspot 720 produced four powerful solar
flares. When it exploded a fifth time on January 20th, onlookers were
not surprised.

They should have been. Researchers realize now that the January 20th
blast was something special. It has shaken the foundations of space
weather theory and, possibly, changed the way astronauts are going to
operate when they return to the Moon.

Sunspot 720 unleashed a new kind of solar storm.

Scant minutes after the January 20th flare, a swarm of high-speed
protons
surrounded Earth and the Moon. Thirty minutes later, the most intense
proton storm in decades was underway.

"We've been hit by strong proton storms before, but [never so
quickly],"
says solar physicist Robert Lin of UC Berkeley. "Proton storms normally
develop hours or even days after a flare." This one began in minutes.

Proton storms cause all kinds of problems. They interfere with ham
radio
communications. They zap satellites, causing short circuits and
computer
reboots. Worst of all, they can penetrate the skin of space suits and
make astronauts feel sick.

"An astronaut on the Moon, caught outdoors on January 20th, would have
had almost no time to dash for shelter," says Lin. The storm came fast
and "hard," with proton energies exceeding 100 million electron volts.
These are the kind of high-energy particles that can do damage to human
cells and tissue.

"The last time we saw a storm like this was in February 1956." The
details of that event are uncertain, though, because it happened before
the Space Age. "There were no satellites watching the sun."

According to space weather theory--soon to be revised--this is how a
proton storm develops:

It begins with an explosion, usually above a sunspot. Sunspots are
places where strong magnetic fields poke through the surface of the
Sun.
For reasons no one completely understands, these fields can become
unstable and explode, unleashing as much energy as 10 billion hydrogen
bombs.

From Earth we see a flash of light and X-rays. This is the "solar
flare," and it's the first sign that an explosion has occurred. Light
from the flare reaches Earth in only 8 minutes.

Next, if the explosion is powerful enough, a billion-ton cloud of gas
billows away from the blast site. This is the coronal mass ejection or
"CME." CMEs are relatively slow. Even the fastest ones, traveling one
to
two thousand km/s, take a day or so to reach Earth. You know a CME has
just arrived when you see auroras in the sky.

En route to Earth, CMEs plow through a lot of gaseous material, first
in
the sun's atmosphere and then out in interplanetary space. You thought
space was empty? No. The void between planets is filled with protons
and
other particles from the solar wind. Shock waves in front of the CME
can
accelerate these protons in our direction--hence the proton storm.

"CMEs can account for most proton storms," says Lin, but not the proton
storm of January 20th. According to theory, CMEs can't push material to
Earth quickly enough.

Back to the drawing board: If a CME didn't accelerate the protons, what
did?

"We have an important clue," says Lin. When the explosion occurred,
sunspot 720 was located at a special place on the sun: 60o west
longitude. This means "the sunspot was magnetically connected to
Earth."

He explains: The sun's magnetic field spirals out into the solar system
like water from a lawn sprinkler. (Why? The sun spins like a lawn
sprinkler does.) The magnetic field emerging from solar longitude 60o W
bends around and intersects Earth. Protons are guided by magnetic force
fields so, on January 20th, there was a superhighway for protons
leading
all the way from sunspot 720 to our planet.

"That's how the protons got here," speculates Lin. How they were
accelerated, however, remains a mystery.

What does all this mean for astronauts? Stay inside when there's a big
sunspot located near solar longitude 60o W. Or, if you must go
moonwalking, take a radiation shelter with you. It's not as hard as it
sounds.

Stay tuned for more on this topic in an upcoming Science@NASA story,
"Radiation Shelters: Don't Leave Home Without One."