Data from Japanese spacecraft confirm theories on solar wind
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 frigid 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 about 2 million mph, according to results published today in the journal Science.
“Until now, Alfven waves have been impossible to observe because of limited resolution of available instruments,” said Alexei Pevtsov, a Hinode scientist at NASA in Washington. “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 wind on Earth. Instead of leaves and branches flapping around, though, the solar wind propels a stream of electrically charged gas away from the sun in all directions.
The wind is part of a solar weather machine that generates sunspots, flares and big space storms called coronal mass ejections, which can knock out power grids on Earth. With increasing dependence on technology, scientists know that understanding how the sun works is more than a matter of curiosity.
Predicting major solar events can be a matter of life or death. A big radiation storm in 1972, during the era of U.S. manned lunar exploration, could have had lethal consequences, said Ron Zwickl, a spokesman for the Space Environment Center in Boulder, Colo. If astronauts had been on the moon at the time, “I doubt that any of them would have lived long,” Zwickl said.
Magnetic Alfven waves have long been a leading candidate for explaining the force behind solar wind. Theoretically, they could efficiently transfer energy from the sun’s surface through the corona and into the solar wind.
With a suite of instruments that includes a 20-inch optical telescope, an X-ray telescope and a spectrometer, Hinode has been able to observe the sun’s exterior with unusual precision.
“Hinode has allowed us to see the fine structures,” said Bart De Pontieu, a solar physicist with the Lockheed Martin Solar and Astrophysics Lab in Palo Alto.
The spacecraft has been able to home in 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, because of the influence of the Alfven waves, De Pontieu said.
Hinode is helping scientists understand the importance of the chromosphere, he said. “A lot of clues to what happens” elsewhere in the sun “can be found in the chromosphere.”
