Every second, the Sun flings over 1 million tons of matter into space, forming what we call solar wind. It's composed of plasma, which is an extremely hot substance in which the elements have separated into positive ions and their lost electrons. With a density of six ions per cubic centimeter, as opposed to Earth's millions of ions in the same volume of atmosphere, one wouldn"t expect much from solar wind. However, its velocity varies between 750 and 500 kilometers per second and it has an average temperature, near Earth, of 150,000 degrees Kelvin. Occasionally, it even reaches speeds of up to 1000 km/s. Proof of the existence of solar wind was first put forward in 1951 by Ludwing Biermann, who suggested that comet tails are always directed away from the Sun because they are pushed by a continuous flow of charged particles streaming out from the Sun, or solar wind. .
These charged particles of solar wind envelop our solar system in a magnetic bubble extending far out into interstellar space. The solar wind appears to drag the Sun's magnetic field with it as it expands, creating a huge region of magnetic influence. The heliosphere allows life on Earth to survive, shielding us from cosmic rays (very energetic particles generated far away in the universe) which can cause damage to living cells. .
The shape of the heliosphere, although never fully observed, is thought to be like a protective bubble encasing the solar system. However, it isn"t symmetrical around the Sun. The motion through interstellar gas compresses it at the front and drags it out into a tail at the back, much like a planetary magnetosphere. Recent data from the Voyager 1 and 2 space probes have shed new light on the subject. Since 1992, fifteen years after their launch for a supposed four-year flight, they have begun picking up intense low-frequency radio emissions coming from beyond the solar system with specialized radio antennas, called the plasma wave subsystem.
