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Solar Wind

One of the biggest mysteries about the Sun has been why the corona is so hot. The surface of the Sun has a temperature of about 6000 Centigrade, but the coronal temperature was over 1.2 million degrees Centigrade. There were several detailed theories about how this could be, but all of them needed data that was as yet unavailable to confirm them.

This changed in the 1990s when a new generation of research satellites came into use. The secret of the corona's temperature seemed to lie in the complex and continuous formation of granule-sized magnetic loops all over the Sun's surface. As these loops short-circuit and reconnect with their neighbors, they heat the solar gases to over one million degrees. The gases then escape from the surface and evaporated into the corona.

Some of the gases become trapped in the coronal magnetic field so that a spectacular solar atmosphere forms. You can see this during a total solar eclipse. Other gases flow out into the solar system on magnetic field lines that do not swing back to the surface of the Sun, and it is here that the solar wind owes much of its existence.

Source:NASA

The solar wind travels at about 450 kilometers/second but can gust up to 1,700 kilometers/second or more if there is a powerful coronal mass ejection passing by. The solar wind is composed of the same atoms that make up the Sun itself, and in nearly the same abundances. For example, out of 100 atoms in the wind, there are about 75 hydrogen atoms for every 23 helium atoms.

The solar wind contains overlapping patterns of high-speed and slow-speed flows, as fast moving particles from so-called coronal holes have easy times escaping from the magnetic conditions near the solar surface. At any given time, there are sectors where the polarity reverses sometimes 5-10 times around the circumference of the Earth's orbit. Eventually the solar wind collides with atoms from interstellar gases surrounding the solar system out beyond Pluto, forming a shock front and a vast, but invisible, bubble.

The solar wind is like a conveyor belt that transmits the outcomes of events on the solar surface into interplanetary space. It can carry both particles and magnetic fields that were formerly a part of the solar surface. When this wind encounters a distant planet, it causes changes in the electrical properties of the space around the planet that can have significant impacts on planetary atmospheres and especially on their own magnetic fields, if they have one. Venus and Mars bear the full brunt of the streaming wind, and lose some of their atmosphere into the wind. Other planets such as the Earth, Jupiter, Saturn, Uranus and Neptune have powerful magnetic fields of their own, which act as shields for much of the solar wind's forces.

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