Japanese Spacecraft Confirms Magnetic Wave Theory
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Data from the Japanese Hinode spacecraft have confirmed that a set of long-theorized magnetic waves help power the solar wind that drives charged particles to the boundary of the solar system. Called Alfven waves in honor of the Swedish scientist who proposed their existence 60 years ago, they play an important role in accelerating the solar wind to speeds of around 2 million mph, according to results to be published Friday in the journal Science.
“Until now, Alfven waves have been impossible to observe because of limited resolution of available instruments,” a Hinode scientist at NASA in Washington, D.C., Alexei Pevtsov, said. “With the help of Hinode, we are now able to see direct evidence of Alfven waves.”
Hinode was launched in September 2006, the latest in a string of spacecraft trying to unravel long-standing solar mysteries, such as the origin of the sun’s huge magnetic field, and the explanation behind the fact that the sun’s atmosphere — or corona — is nearly a million degrees hotter than the surface.
In many ways, scientists say, the solar wind behaves like a wind blowing on Earth. Instead of leaves and tree branches flopping around, the solar wind propels a stream of electrically charged gas away from the sun in all directions.
The solar wind is part of a solar weather machine that generates sunspots, flares and big space storms called coronal mass ejections, which can knock power grids on Earth out of service. As human societies have grown more dependent upon technology, scientists have come to realize that understanding how the sun works is more than a matter of curiosity. Lives can depend on being able to predict major solar events. A big radiation storm in 1972, during America’s era of manned lunar exploration, could have had lethal consequences, according to Ron Zwickl, a spokesman for the Space Environment Center in Boulder, Colo. Had there been astronauts on the moon at the time, “I doubt that any of them would have lived as long,” Mr. Zwickl said.
Magnetic Alfven waves have always been a leading candidate as the force behind the solar wind. Theoretically, they could efficiently transfer energy from the surface through the corona and into the solar wind.
With a suite of instruments including a 20-inch optical telescope, an X-ray telescope and a spectrometer, Hinode has been able to observe the sun’s boiling exterior with unusual precision. “Hinode has allowed us to see the fine structures,” a solar physicist with the Lockheed Martin Solar and Astrophysics Lab in Palo Alto, Calif., Bart De Pontieu, said. The spacecraft has been able to focus on 125-mile-wide eruptions from the surface called spicules. These spicules can be seen waving back and forth in the sun’s chromosphere, the narrow region between the surface and the corona, due to the influence of the Alfven waves, Mr. De Pontieu said.
According to Mr. De Pontieu, Hinode is helping scientists to understand the importance of the chromosphere. “A lot of clues to what happens” elsewhere in the sun “can be found in the chromosphere,” Mr. De Pontieu said.