Solar Wind

The solar wind is loose electrons and the ions (atoms) from which they have been stripped (hydrogen, helium, etc.) shot out from the sun's corona (the very outer layer of the sun) at very high speeds (300-900 Km/sec - or about 1,000,000 miles per hour). The solar wind is made up of plasma, which is a kind of liquified gas. It amounts to a total of one million tons of matter per second. It is the force that blows ion comet tails so that they face away from the sun. It affects the magnetosphere of the Earth, as well as the atmosphere.

Solar winds as we understand them were first hypothesized in 1943 by a German Astronomer, Cuno Hoffmeister. But the actual mechanics of how solar winds work was developed by Eugene Parker at the University of Chicago in 1958. The solar wind was later confirmed by instrument readings from space craft.1

All astral bodies have gravity. The gravitational forces, if great enough, will hold down an atmosphere of gasses. Nevertheless, individual or groups of atoms, electrons, and protons, will accelerate to a speed where they overcome the gravitational force and fly away from the atmosphere. This happens a lot on the sun where the super heat of the corona accelerates electrons and protons, shooting them away from the sun (even with its powerful gravitational force). Magnetic forces may also be in play in the acceleration process. Though the solar wind is powerful, it is not very dense by the time it reaches the Earth. Even so, its effects are evident even beyond the outermost planets in the solar system. The area within which the solar winds have an effect is called the helioshpere. The point at which solar winds are no longer detectable is called the heliopause.

The Interplanetary Magnetic Field

Flows of particles follow magnetic lines within the corona. As they shoot out they carry these magnetic lines with them2. This creates an interplanetary magnetic field. The magnetic fields go out along open magnetic lines that extend out into space. Some of these lines are positive and some negative. Because the sun rotates on an axis at a different rate than the Earth orbits the sun, the Earth experiences alternating positive and negative fields.3

The solar wind and the interplanetary magnetic field react with the Earth's own magnetic field. It forces the field back toward the Earth on the sunny side (to a distance equal to about 10 times the radius of the Earth). Meanwhile, on the nightside of the Earth a long tail forms. This area is called the magnetosphere.

The Solar Wind and the Atmosphere of Planets

The atmospheres of planets without magnetic fields are negatively affected by the solar wind. The wind effectively strips gasses off such planets. Thus Mercury does not hold down an atmosphere. Mars has a minimal atmosphere, but the solar winds are thought to have decreased it significantly over the eons. The moon also does not have a magnetosphere and is not close enough to be protected by the Earth's magnetic field. Thus the solar wind has stripped off the gasses. However, the solar wind does leave deposits of ions and particles on such planets that might prove useful to future colonization efforts.

The Solar Wind as a Means of Propulsion

Long ago it had been assumed by scientists and engineers that the solar wind could be used as a means of propulsion, especially in a direction away from the sun. Johannes Kepler, the great astronomer, in the 1600s observed the fact that the tails of comets faced away from the sun. At that point he conjectured on the possibilities. Though interesting in theory, it turns out that the force moving a solar sail would not be from the pressure of the streaming molecules from the solar wind. The propelling force would be photons from the light of the sun. Recent ideas include using a mylar sail to catch the photons. However, this would probably prove too heavy. Other promising materials are being researched such as carbon fibers. The attraction of a solar sail is that it would allow propulsion without the need of carrying fuel, or propellants, or the necessary heavy engines. If a solar sail proves practicable it could actually fly five times faster than conventional rockets. Microwave transmitters and lasers might also be used to help accelerate the craft to up to 1/10th of the speed of light.4

< Why the Moon Waxes and Wanes | Sunspots: Spots on the Sun >

  1. The Solar Wind
  2. FusEdWeb
  3. Interplanetary Magnetic Field
  4. NASA on Solar Sails

Interesting Fact:

The solar wind was first detected by Johannes Kepler when he noticed that the tails of comets always face away from the sun.

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