Mechanisms for solar wind discovered by Japanese Hinode spacecraft

William Atkins
Monday, 10 December 2007 20:43

Science - Space

An international group of scientists using the Hinode spacecraft have found that two mechanisms produce the solar wind. How the solar wind was produced was previously not fully understood by scientists.               

The solar wind is a stream of electrically charged gas particles (plasma), consisting mostly of high-energy electrons and protons, that are ejected out by the upper atmosphere of the Sun at high rates of speed—upwards of one million miles per hour (1.6 million kilometers per hour).

The solar wind races toward the Earth, bombards it, and then moves onward past our planet. While it interacts with Earth, is can harm (or, at least disrupt) communications equipment such as weather satellites orbiting around the Earth and power stations on the surface of Earth.

For the most part, the Earth’s magnetic field counters the affects of the solar wind, but not always. Humans on the Earth only notice the solar wind when it is very strong, at which times it produces aurora (northern and southern lights) and geomagnetic storms.

Although we know where the solar wind comes from and what it consists of, scientists did not know how it was produced. Now, due to work by European, Japanese, and U.S. scientists on the Hinode satellite, we know that two mechanisms are at work at producing the solar wind.

First, the magnetic field of the Sun changes constantly. The variation of the solar magnetic field produce what are called Alfen waves, defined as strong magnetohydrodynamic (or hydromagnetic) waves that are created in the plasma of the Sun’s corona and move along lines of magnetic force in plasma.

They are named after Swedish plasma physicist Hannes Olof Gösta Alfvén (1908-1995), who won the Nobel Prize in 1970 for discoveries in magnetohydrodynamics. The Alfen waves accelerate the solar wind and help to blow it out into space, with some of the solar wind eventually hitting the Earth.

Second, the chromosphere of the Sun contains many Alfven waves. Many of them are ejected into the corona, the layer next to it and further out from the interior of the Sun. When enough of these Alfven waves get into the chromosphere they can produce the solar wind.

The Solar Optical Telescope within Hinode found these Alfven waves, which previously were known to exist but never seen. The instruments aboard Hinode are stronger than ever before used, They were able to see the Alfven waves for the first time and, in the process, learn the mechanisms used to create the solar wind.
The conclusions produced by this international team of scientists is published in the journal Science.