A study of satellite images shows that during strong solar storms, Earth's magnetic field dips a shoulder of ionized gas, or plasma, into the onslaught and sprouts a plasma tail on its backside. The planet's magnetic field also splits the Sun's energy into two separate streams.

These discoveries, along with other surprises in the images, are expected to improve space-weather forecasting.

The curious features were spotted by NASA's IMAGE satellite. The spacecraft studies the field of magnetic energy that emanates from the planet's poles and encircles the globe in an invisible protective sheath.

This so-called magnetosphere is Earth's front line against space weather.

Scientists therefore want to better understand what goes on when the solar wind, made up of protons and electrons, strikes the magnetosphere. The interaction is known to push the magnetosphere into a teardrop shape that extends beyond the Moon on Earth's nightside. (The plasma tail that forms during solar storms is loosely linked to the magnetosphere's teardrop shape).

When the solar wind whips up a strong storm, it can knock out radio communications, disrupt satellites and even threaten power grids on Earth.

So researchers used the satellite's ultraviolet imager to peer inside Earth's magnetosphere. They studied a region of space full of ionized gas, created when atoms lose electrons. Scientists call the stuff plasma. It is known to interact with the solar wind, but images of the interaction have been elusive.

The new study, led by James Burch of the Southwest Research Institute, produced the first global images of this region of space known as Earth's plasmasphere. The results are reported in the Jan. 26 issue of the journal Science.

Burch and his colleagues discovered that during strong solar storms, a buildup of plasma, described as a shoulder, forms on the side of the Earth facing the storm. On Earth's backside, the plasma is pulled into a long tail that curves out into space and points back toward the Sun.

"The plasma tails were predicted but were very controversial," Burch told SPACE.com. The tails are thought to form when helium ions near the boundary of the magnetosphere are dragged by the solar wind, but then escape the magnetosphere and are forced by the storm back toward the Sun.

"The shoulder feature was a surprise," Burch said, "and we are still trying to explain it."

The electrons and protons of the solar wind are directed around the planet by Earth's magnetic field lines. When these charged particles penetrate to inner portions of the magnetosphere, they interact with the plasmasphere, exciting gases to produce the colorful northern and southern lights known as the aurora.

For two decades, researchers have imaged the electron stream, but Burch and his colleagues have now measured the less noticeable proton stream. Both streams produce auroras, though not all of it is the bright and colorful variety seen from the ground at high latitudes during geomagnetic storms.

Burch's team found that the proton stream, as theorized, enters the atmosphere at lower latitudes -- farther from the magnetic poles -- than the electron stream. The researchers discovered, in fact, that aurorae at higher latitudes are devoid of protons.

Burch explained why: "The electrons have much lower momentum because they are much lighter and so they are deflected around the Earth first," he said. "The protons, like big bowling balls, plow farther into the magnetic field."

Both streams of charged particles are eventually deflected around the planet, but Earth's magnetic field lines tend to direct a portion of each toward the poles.

While solar storms can occur at any time, the Sun is currently in the midst of a peak of an 11-year cycle of activity. Storms were more frequent than normal during 2000, and experts say heightened activity may continue for another two years.

Click here for today's aurora forecast and live cam.