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Magnetic Twisters "Dance" Across Mercury, Study Says

Rebecca Carroll
for National Geographic News
April 30, 2009
 
The ever-present supersonic gale from the sun creates never-before-seen magnetic "twisters" that "dance" across Mercury's magnetic field and occasionally touch down on its surface, new observations have revealed.

These invisible formations, made of high-energy electrons, kick up material from Mercury's surface and send it flying into the tiny, rocky planet's tenuous atmosphere, according to new research.

Part of a suite of new findings based on October 2008 data from the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft, the study could help explain why Mercury's thin, inconstant atmosphere is so, well, mercurial.

The findings, published this week in the journal Science, could also add to scientists' understanding of the phenomenon called space weather.

With a period of strong solar storms predicted to start in 2012 that could interfere with satellites and disrupt power grids on Earth, better understanding of solar wind is a pressing need, scientists say.

(Related: "Magnetic-Shield Cracks Found; Big Solar Storms Expected.")

Surprisingly Intense

Mercury's magnetic twisters are created when solar wind—which is actually a stream of charged particles—triggers a process on the tiny planet called magnetic reconnection.

This is when magnetic field lines flowing from the sun splice together with the field lines around Mercury.

The connection transfers solar wind energy into the planetary magnetic field and sends charged particles shooting toward the planet along the field lines.

Bundles of these connected field lines then penetrate the planet's magnetic boundary and their particles are sent whirling by the solar wind, forming the twisters.

On Earth, energy from magnetic reconnection "lights up" atoms in our much thicker atmosphere, creating the shimmering auroras at our planet's poles.

(Related: "Giant 'Space Tornadoes' Spark Auroras on Earth.")

What surprised scientists is that reconnection on Mercury is ten times more intense than it is on Earth, said study author James Slavin of the NASA Goddard Space Flight in Greenbelt, Maryland.

It's reasonable to think that magnetic reconnection would be stronger on Mercury, the closest planet to the sun. But researchers were anticipating it would only be about two or three times more intense than on Earth, Slavin said.

Figuring out why the process is so much stronger than expected could shed light on how solar wind affects magnetic fields around other planets, including Earth.

Despite the stronger reconnection events, Slavin said, "at Mercury, we don't have an atmosphere that's dense enough or of the right kind of gas probably to produce anything we would recognize as auroras."

Still, similar invisible currents may exist along those same magnetic regions of Mercury.

"It's possible there may be a little ring around both poles of Mercury, where the surface is ever so slightly warmer than the other latitudes of the planet," Slavin said. (See a photo of "hyper auroras" on Jupiter.)

Solar Erosion

The new observations also show that—like the twisters—the solar wind directly plays a part in shaping the mysterious planet's surface.

Earth, Jupiter, and Saturn have dense atmospheres and strong magnetic shields, protections that deflect the full force of the winds from reaching their surfaces.

On Venus and Mars, meanwhile, there're little or no magnetic fields but some atmospheres, so "there's a tendency for the solar wind to strip away the atmosphere over the eons," Slavin said.

(Related: "Stars Can Strip Gas Giants Naked.")

"In the case of a body like Mercury, where you don't have a planetary atmosphere, or you have an extremely tenuous one, you have a situation where the solar wind … actually erodes the surface somewhat. It's a very small amount," Slavin said.

Sean Solomon of the Carnegie Institution in Washington, D.C., who was involved in the research, noted that there was much more magnetic activity during the October flyby than during MESSENGER's first encounter in January 2008. (See photos from the first Mercury flyby.)

"Mercury is a lot more complicated and its processes are a lot more dynamic than we knew," Solomon said.
 

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