Twin NASA spacecraft have provided scientists with their
first view of the speed, trajectory, and three-dimensional shape of
powerful explosions from the sun known as coronal mass ejections, or
CMEs. This new capability will dramatically enhance scientists’
ability to predict if and how these solar tsunamis could affect
Earth.

When directed toward our planet, these ejections can be breathtakingly
beautiful and yet potentially cause damaging effects worldwide. The
brightly colored phenomena known as auroras — more commonly called
Northern or Southern Lights — are examples of Earth’s upper
atmosphere harmlessly being disturbed by a CME. However, ejections
can produce a form of solar cosmic rays that can be hazardous to
spacecraft, astronauts and technology on Earth.

Space weather produces disturbances in electromagnetic fields on Earth
that can induce extreme currents in wires, disrupting power lines and
causing wide-spread blackouts. These sun storms can interfere with
communications between ground controllers and satellites and with
airplane pilots flying near Earth’s poles. Radio noise from the storm
also can disrupt cell phone service. Space weather has been
recognized as causing problems with new technology since the
invention of the telegraph in the 19th century.

NASA’s twin Solar Terrestrial Relations Observatory, or STEREO,
spacecraft are providing the unique scientific tool to study these
ejections as never before. Launched in October 2006, STEREO’s nearly
identical observatories can make simultaneous observations of these
ejections of plasma and magnetic energy that originate from the sun’s
outer atmosphere, or corona. The spacecraft are stationed at
different vantage points. One leads Earth in its orbit around the
sun, while the other trails the planet.

Using three-dimensional observations, solar physicists can examine a
CME’s structure, velocity, mass, and direction in the corona while
tracking it through interplanetary space. These measurements can help
determine when a CME will reach Earth and predict how much energy it
will deliver to our magnetosphere, which is Earth’s protective
magnetic shield.

“Before this unique mission, measurements and the subsequent data of a
CME observed near the sun had to wait until the ejections arrived at
Earth three to seven days later,” said Angelos Vourlidas, a solar
physicist at the Naval Research Laboratory in Washington. Vourlidas
is a project scientist for the Sun Earth Connection Coronal and
Heliospheric Investigation, STEREO’s key science instrument suite.
“Now we can see a CME from the time it leaves the solar surface until
it reaches Earth, and we can reconstruct the event in 3D directly
from the images.”

These ejections carry billions of tons of plasma into space at
thousands of miles per hour. This plasma, which carries with it some
of the magnetic field from the corona, can create a large, moving
disturbance in space that produces a shock wave. The wave can
accelerate some of the surrounding particles to high energies that
can produce a form of solar cosmic rays. This process also can create
disruptive space weather during and following the CME’s interaction
with Earth’s magnetosphere and upper atmosphere.

“The new vantage point of these spacecraft has revolutionized the
study of solar physics,” said Madhulika Guhathakurta, STEREO program
scientist at NASA Headquarters in Washington. “We can better
determine the impact of CME effects on Earth because of our new
ability to observe in 3D.”

STEREO is part of NASA’s Solar Terrestrial Probes Program in NASA’s
Science Mission Directorate in Washington. The program seeks to
understand the fundamental physical processes of the space
environment from the sun to Earth and other planets.

The Solar Terrestrial Probes Program also seeks to understand how
society, technological systems and the habitability of planets are
affected by solar processes. This information may lead to a better
ability to predict extreme and dynamic conditions in space, and the
development of new technologies to increase safety and productivity
of human and robotic space exploration.

For more information about NASA’s STEREO mission, visit:
http://www.nasa.gov/stereo