A three-spacecraft collaboration recorded for the first time the
entire initiation process of a high-speed eruption of electrified gas
from the Sun, providing clues about the Sun’s secret recipe for
stormy weather. The April 21, 2002 observation confirmed the
predominant scenario for how these eruptions, called Coronal Mass
Ejections, are blasted from the Sun.
The three spacecraft involved were NASA’s Reuven Ramaty High Energy
Solar Spectroscopic Imager (RHESSI), which takes pictures of flaring
regions using the Sun’s high-energy X-rays and gamma rays; NASA’s
Transition Region and Coronal Explorer (TRACE), which makes images
using ultraviolet light from the Sun; and the Solar and Heliospheric
Observatory (SOHO) spacecraft, a collaboration between NASA and the
European Space Agency.
“This was the first time that we have been able to identify and study
in detail the region on the Sun where the initiation and acceleration
of a coronal mass ejection occurs,” said Dr. Peter Gallagher,
research scientist for RHESSI and SOHO at NASA’s Goddard Space Flight
Center, Greenbelt, Md., and lead author of two papers on this
research. “We now have a better understanding of how the energy
release above the surface of the Sun relates to the ejection of
material, perhaps allowing some real-time forecasts.” The results are
being presented today during a meeting of the American Astronomical
Society’s Solar Physics Division in a press conference at the Johns
Hopkins University Applied Physics Laboratory, Laurel, Md.
Coronal Mass Ejections (CME) are often associated with solar flares.
A flare is a giant explosion in the solar atmosphere that spews
radiation and results in the heating of solar gas and the
acceleration of particles to nearly the speed of light. Both events
can be initiated in a matter of seconds, making their joint
observations difficult to coordinate.
The twisting and snapping of magnetic field lines on the Sun, called
magnetic reconnection, seem to cause CMEs and solar flares. When
these fields snap from the buildup of magnetic energy, plasma is
heated and particles are accelerated, resulting in massive explosions
and emitting radiation ranging from radio waves to X-rays.
Frequently, a CME and flare will burst from the same region of the
Sun nearly simultaneously. Just like the debate over whether the
chicken or the egg came first, solar researchers discuss whether
flares cause CMEs or the reverse, or if they are more loosely
associated.
The April 21, 2002 observation confirmed the predominant scenario for
high-speed CMEs (those moving at one million to 5 million miles per
hour or 1.6 million to 8 million km/hr.). This is where solar
magnetic fields act like a lid, holding down a blob of gas (CME) that
is trying to rise. Somehow, the magnetic lid opens, possibly as a
result of magnetic reconnection and the generation of a flare, and
then the CME rises from the Sun, dragging the magnetic fields with
it. Magnetic reconnection continues to energize the associated flare
for over 12 hours.
All three spacecraft played vital roles in confirming that this was
the process. First, RHESSI saw a gradually increasing burst of X-rays
announcing the start of the flare. TRACE observed the CME in the
extreme ultraviolet as it began to rise from the Sun. Several minutes
later, RHESSI saw a burst of high energy X-rays under the erupting
CME, and TRACE saw a similar explosion of ultraviolet rays, both
indicating a large flare. SOHO then captured the CME as it continued
moving away from the Sun.
“Each of these spacecraft is quite complementary,” said Gallagher.
“It’s only through their coordination in this observation that we’re
now able to understand the predominant scenario for these fast, large
coronal mass ejections and the associated flares.”
The current results feed into the decades-old controversy over
whether solar flares cause coronal mass ejections, or vice versa.
While the first signs of the flare occur before the CME liftoff, the
bulk of the flare energy is released later, after the CME has already
been accelerated. The two phenomena are revealed to be merely
different aspects of the same event, according to the team. For
images and more information, refer to:
