The sun warms us, bathes us in lightand also blasts us periodically with billions of tons of fast-moving ionized gas. These explosions, known as coronal mass ejections (CMEs), produce stunning auroras such as the southern and northern lights but can also wipe out power and communications systems as they wreak havoc on Earth's magnetic field.
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Image: SOHO/NASA/ESA

FIRE-EATER. Don't let the cool blue of these images from SOHO's LASCO instrument fool you. They show a powerful coronal mass ejection erupting from the sun (top left), followed by a second (top right) that consumes it (bottom left) and quickly moves out into space (bottom right).

Now that the sun is at a solar maximumthe latest peak in its 11-year activity cycleCMEs are expected to become more frequent, occurring as much as several times a day. And according to a recent report, a particularly damaging type of CME, which cannibalizes slower moving ejections to gain strength, may also take place more often in the months to come.

"Coronal mass ejection cannibalism is the most violent form of interaction between CMEs," says Natchimuthuk Gopalswamy of the Catholic University of America, who presented new findings this week with colleagues from the NASA Goddard Space Flight Center and the Naval Research Laboratory at a meeting of the European Geophysical Society in Nice, France. "This happens when a slow CME is expelled before a fast one from the same general region on the sun. The fast CME simply gobbles up the slow CME, resulting in a single CME beyond the region of interaction."

The series of images at the left depict a cannibalistic CME in action. In the first frame, a huge bubble of plasma erupts from the sun's outer atmosphere and begins barreling into space in the second frame. Another CME bursts forth in the third frame from the same area at a faster speed. In fact, CMEs can accelerate up to five million miles per hour. In the fourth frame, the second CME closes in on the first, overtaking it in the fifth frame. The last image shows a new hybrid CME.

Strange outbursts of radio emissions away from the sundetected using the Solar and Heliospheric Observatory (SOHO) spacecraftfirst tipped off scientists to these cannibalistic clouds. When Gopalswamy and his colleagues sought the source of the sounds, they discovered that their timing coincided with images of CMEs. Further analysis revealed that the radio emissions took place specifically when a speeding CME interacted with and consumed another.

Because these interactions change the speed of an eruption, they alter the estimated arrival time of the resulting magnetic storm on Earth, throwing off scientists' best space-weather predictions. The researchers also believe that cannibal eruptions may explain larger so-called complex ejecta CME clouds. When these complex ejecta CMEs hit Earth's magnetic field, they distort its shape more dramatically and thus produce especially protracted magnetic storms.

Since the first cannibalistic CME was discovered nearly four years ago, scientists have witnessed an additional 21 such eruptions. But they suspect that many more events take place and simply aren't detected because they lack the energy needed to produce a radio outburst. "Collisions between CMEs may be more common than previously thought," Gopalswamy notes, "and may play a key role in determining the interplanetary traffic of CMEs."