Scientists explain mysterious plasma jets on the Sun (Forwarded)

Lockheed Martin

Media Contact:
Buddy Nelson, (510) 797-0349; e-mail,
Bart DePontieu, (650) 424-3094; e-mail,

July 28, 2004

SCIENTISTS EXPLAIN MYSTERIOUS PLASMA JETS ON THE SUN

Palo Alto, Calif. -- Solar physicists from Lockheed Martin [NYSE: LMT] and the
Solar Physics and upper-Atmosphere Research Group at the Department of Applied
Mathematics of the University of Sheffield, UK have used computer modeling and
some of the highest resolution images ever taken of the solar atmosphere to
explain the cause of supersonic jets that continuously shoot through the low
atmosphere of the Sun.

Their results, which appear as the cover story in tomorrow's issue of the
journal Nature, directly address the origin of these jets, called spicules. The
origin of spicules has been a mystery since their discovery in 1877. These
findings may well lead to a better understanding of how matter is propelled
upward into the solar corona to form the solar wind, a stream of particles
continuously emitted by the Sun that sweeps past Earth's orbit. Disturbances in
the solar wind can influence the upper atmosphere and space environment around
the Earth and damage satellites in orbit.

"The combination of computer modeling, new high resolution images taken with the
Swedish 1-meter Solar Telescope (SST) on the island of La Palma, Spain and data
taken simultaneously with two satellites in space, was crucial to figure out how
spicules are formed," said Dr. Bart De Pontieu, one of the main investigators on
the study, and solar physicist at the Lockheed Martin Solar and Astrophysics Lab
(LMSAL) at the company's Advanced Technology Center in Palo Alto, Calif. "We
used a computer model to provide the missing link between observations of the
surface of the Sun, taken with the MDI instrument onboard ESA/NASA's Solar and
Heliospheric Observatory (SOHO) satellite, and observations of the jets in the
low solar atmosphere taken with the SST and NASA's Transition Region and Coronal
Explorer (TRACE) satellite."

Spicules are jets of gas or plasma propelled upwards from the surface of the
Sun. They shoot into its atmosphere or corona at supersonic speeds of about
50,000 miles per hour, and reach heights of 3,000 miles above the solar surface
in less than five minutes. Although there are over 100,000 spicules at any time
in the Sun's low atmosphere, or chromosphere, they remain largely unexplained,
in part because observations are difficult for objects with so brief a lifetime
(about five minutes) and relatively small size (300 miles diameter).

"By simultaneously taking a series of high resolution images with the Swedish
Solar Telescope, showing details down to 80 miles, and with the TRACE satellite,
we discovered that these jets often occur periodically, usually every five
minutes or so, at the same location," said Professor Robertus Erdélyi von
Fáy-Siebenbürgen, the other main investigator on the study, and professor in
applied mathematics at the Solar Physics and upper-Atmosphere Research Group of
the University of Sheffield, UK. "We developed a computer model of the Sun's
atmosphere to show that the periodicity of the spicules is caused by sound waves
at the solar surface that have the same five minute period."

The sound waves at the solar surface are usually damped before they can reach
the Sun's atmosphere. However, De Pontieu, Erdélyi and Stewart James, a newly
graduated Ph.D. under the supervision of Professor Erdélyi at the University of
Sheffield, found that under certain conditions, the sound waves can penetrate
through the damping zone and leak into the solar atmosphere. Their computer
model shows that after the sound waves leak into the atmosphere, they develop
into shock waves that propel matter upwards, forming a spicule.

De Pontieu and his colleagues measured actual waves and oscillations at the
surface of the Sun, using these measurements to drive their computer model of
the solar atmosphere, which then predicted when jets of gas should shoot up.
They were pleasantly surprised to see that the model predicts very accurately
when jets should be observed on the Sun with the SST and TRACE.

"Spicules carry more than 100 times the mass into the Sun's atmosphere required
to feed the solar wind," said De Pontieu, "which means that they are of huge
importance for the balance of how much mass goes into and out of the corona."
With the origins of spicules revealed, it will be possible to study whether the
mass that spicules carry into the solar corona contributes to the solar wind.
Future studies will also focus on the role the shock waves may play in the
higher solar atmosphere or corona.

The results of this study are in a paper published in the journal Nature. The
authors are Dr. Bart De Pontieu of Lockheed Martin Solar and Astrophysics Lab,
and Professor Robertus Erdélyi von Fáy-Siebenbürgen and Dr. Stewart James of The
Solar Physics and upper-Atmosphere Research Group at the Department of Applied
Mathematics, University of Sheffield, UK. Funding for the studies came from
NASA, the Particle Physics and Astronomy Research Council of the UK and the
Hungarian National Science Foundation.

The Lockheed Martin Solar and Astrophysics Lab is part of Lockheed Martin's
Advanced Technology Center -- the research and development organization of
Lockheed Martin Space Systems Company. Headquartered in Bethesda, Md., Lockheed
Martin employs about 130,000 people worldwide and is principally engaged in the
research, design, development, manufacture and integration of advanced
technology systems, products and services. The corporation reported 2003 sales
of $31.8 billion.

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NOTE TO EDITORS:
Low- and high-resolution JPEG image files and solar movies of the discovery are
available at the following URL:
http://www.lmsal.com/Press/spicules2004/index.html