Going to the Moon? Be careful. A new kind of solar storm can take you by surprise.
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.
Right:
The Jan. 20th proton storm photographed from space by the Solar and
Heliospheric Observatory (SOHO). The many speckles are solar protons
striking the spacecraft's digital camera. [More]
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.
Above:
Sunspot 720 erupting on Jan. 15th, photographed by Jack
Newton.
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.
Above:
The sun's magnetic field spirals like water from a lawn sprinkler.
The field line emerging from solar longitude 60 degrees west usually
leads to Earth. [More]
"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."
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More Information
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Sickening Solar Flares -- (Science@NASA) NASA researchers discuss what a big proton storm might do to someone on the Moon.
Mysterious Cancer -- (Science@NASA) Researchers agree that space radiation can cause cancer. They're just not sure how.
The Biggest Explosions in the Solar System -- (Science@NASA) NASA's RHESSI spacecraft aims to solve an explosive riddle: the origin of solar flares. Robert Lin is the principle investigator of this mission.
Spaceweather.com -- the latest news about solar storms
Editor's note: Near the end of this story, we learn that sunspot 720 was located at 60o W solar longitude. What is solar longitude? Astronomers use solar latitude and longitude to specify the location of sunspots on the surface of the sun. Zero degrees solar longitude defines a line running north-south through the center of the sun's disk as seen from Earth. This is the sun's central meridian. 60o W solar longitude is a similar line 60 degrees west of the sun's central meridian. Although the sun rotates, once every 27 days, these longitude markings remain fixed with respect to an observer on Earth.
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Feature Author: Dr. Tony
Phillips
Feature Production Editor: Dr. Tony
Phillips
Feature Production Credit: Science@NASA
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