Solar
Flare Leaves Sun Quaking
Scientists have shown for
the first time that solar
flares produce seismic waves in the Sun's
interior that closely resemble those created by
earthquakes on our planet. The researchers observed a
flare-generated solar quake that contained about 40,000
times the energy released in the great earthquake that
devastated San Francisco in 1906. The amount of energy
released was enough to power the United States for 20
years at its current level of consumption, and was
equivalent to an 11.3 magnitude earthquake, scientists
calculated.
Dr.
Alexander G. Kosovichev, a senior research scientist
from Stanford University, and Dr.
Valentina V. Zharkova from Glasgow (United Kingdom)
University found the tell-tale seismic signature in data
on the Sun's surface collected by the Michelson
Doppler Imager onboard the Solar
and Heliospheric Observatory (SOHO) spacecraft
immediately following a moderate-sized flare on July 9,
1996.
"Although the flare was a
moderate one, it still released an immense amount of
energy," said Dr. Craig Deforest, a researcher with
the SOHO project. "The energy released is equal to
completely covering the Earth's
continents with a yard of dynamite and detonating it all
at once."
SOHO is a joint project of the
European Space Agency and NASA. The finding is reported
in the May 28 issue of the journal Nature, and will be
the subject of a press conference at the spring meeting
of the American Geophysical Union in Boston, Mass., May
27 at 9 a.m. EDT.
The solar quake that the science team
recorded looks much like ripples spreading from a rock
dropped into a pool of water. But over the course of an
hour, the solar waves traveled for a distance equal to
10 Earth diameters before fading into the fiery
background of the Sun's photosphere. Unlike water
ripples that travel outward at a constant velocity, the
solar waves accelerated from an initial speed of 22,000
miles per hour to a maximum of 250,000 miles per hour
before disappearing.
"People have looked for evidence
of seismic waves from flares before, but they didn't
have a theory so they didn't know where to look,"
says Kosovichev.
Several years ago Kosovichev and
Zharkova developed a theory that can explain how a
flare, which explodes in space above the Sun's surface,
can generate a major seismic wave in the Sun's interior.
According to the currently accepted model of solar
flares, the primary explosion creates high-energy
electrons (electrically charged subatomic particles).
These are funneled down into a magnetic flux tube, an
invisible tube of magnetic energy, and produce X-rays,
microwaves and a shock wave that heats the solar
surface. Kosovichev and Zharkova developed a theory that
predicts the nature and magnitude of the shock waves
that this beam of energetic electrons should create when
they slam down into the solar atmosphere.
Although their theory directed them to
the right area to search for the seismic waves, the
waves that they found were 10 times stronger than they
had predicted. "They were so strong that you can
see them in the raw data," Kosovichev says.
The solar seismic waves appear to be
compression waves like the "P" waves generated
by an earthquake. They travel throughout the Sun's
interior. In fact, the waves should recombine on the
opposite side of the Sun from the location of the flare
to create a faint duplicate of the original ripple
pattern, Kosovichev predicts.
Now that they know how to find them,
the SOHO scientists say that the seismic waves generated
by solar flares should allow them to verify
independently some of the conditions in the solar
interior that they have inferred from studying the
pattern of waves that are continually ruffling the Sun's
surface.
SOHO is part of the International
Solar-Terrestrial Physics (ISTP) program, a global
effort to observe and understand our star and its
effects on our environment. The ISTP mission includes
more than 20 satellites, coupled with with ground-based
observatories and modeling centers, that allow
scientists to study the Sun,
the Earth,
and the space between them in unprecedented detail. ISTP
is a joint program of NASA, ESA, Japan's Institute for
Astronautical Science, and Russia's Space Research
Institute.
Seismic
Wave Movie
This is a movie of the July 9, 1996
solar quake. The images were made using the Michelson
Doppler Imager onboard the Solar and Heliospheric
Observatory (SOHO) spacecraft, a joint European Space
Agency/NASA project. The white, feathery object in the
center is the solar flare that caused the quake. A solar
flare is an explosion in the atmosphere of the Sun,
caused by the tearing and reconnection of strong magnetic
fields. Although moderate in size, this flare
released an enormous amount of energy. The energy
released is equal to completely covering the Earth's
continents with a yard of dynamite and detonating it all
at once. Some of this energy was transferred to the
solar surface by high speed electrons traveling within
magnetic flux tubes, invisible tubes of magnetic energy.
They produced X-rays,
microwaves and shock waves that heated the solar
surface. These shock waves are the solar quake, and can
be seen as concentric rings spreading outward from
beneath the flare, much like ripples spreading from a
rock dropped into a pool of water. The flare-generated
solar quake contained about 40,000 times the energy
released in the great earthquake that devastated San
Francisco in 1906. The amount of energy released was
enough to power the United States for 20 years at its
current level of consumption. (Courtesy Dr. Alexander
Kosovichev/Stanford University, the European Space
Agency, and NASA - Animation produce by Calvin J.
Hamilton)
Sun Quake Images
These are a sequence of images taken
from the movie of the July 9, 1996 solar quake. The
solar flare that initiates the shock wave is shown in
the first picture. Concentric rings spread out and get
larger and large in the following pictures.
Additional Resources:
Quakes
on the Sun
