Interplanetary space was once believed to exist in a vacuum as empty space - but, due to the many discoveries throughout the past several decades, we now know that is not the case. Interplanetary space contains two primary constituents - the solar wind and planetary magnetospheres.
The solar wind is an extension of the hot, million degree, outer atmosphere of the Sun (corona). It is an electrified gas, or plasma, which consists of free electrons and free atomic nuclei. A candle flame is an example of plasma.
Planetary magnetospheres are the other important constituents of space. A magnetosphere is the region of space surrounding a planet, which is dominated by its magnetic field rather than the solar wind. When the solar wind encounters a planetary magnetic field, the magnetic field deflects the solar wind, and forms a protective cocoon around the planet. This is called the magnetosphere. The solar wind shapes the magnetosphere, compressing it on the sunward side and drawing it out to a long tail on the nightward side. Earth's magnetosphere is especially important because it protects the planet from the potentially lethal particles of the solar wind, which could be damaging to many forms of life.
A planetary magnetosphere forms when the solar wind (the supersonic, ionized gas that flows from the Sun) encounters a planet possessing a large magnetic field. The magnetic field forms a shield around the planet, forcing the solar wind to flow around the magnetosphere. The plasma generated from the magnetic field while outside the magnetosphere populates the region inside the magnetosphere; the solar wind is the dominant plasma.
Two ingredients are necessary in order to generate a planetary magnetic field--an electrically conductive liquid in the interior of the planetary body, and sufficiently rapid rotation to create circulation of the metallic liquid. On Earth, the outer core is composed of a highly conductive liquid alloy of iron and nickel. Earth's rapid rotation, once every 24 hours, creates convection in this electrically conductive liquid, which thereby generates the magnetic field.
Not all planets have magnetic fields. Venus does not have one. This may be due to its extremely slow rotation rate. It takes 243 Earth days for Venus to spin once on its axis. Mars also has no detectable global magnetic field. Although its rotation is rapid enough, it may no longer have an electrically conductive liquid in its interior.
Although most particles from the solar wind are deflected, sometimes they do penetrate the Earth's magnetosphere at the north and south magnetic poles. Here they strike molecules of hydrogen, nitrogen, and oxygen causing them to emit red, green, and blue light. The shimmering glow that is produced are the aurora borealis and aurora australis, or the northern and southern lights.
Some of the visual effects of a planet's magnetosphere and magnetic field can create spectacular light shows at the Poles. These are called auroras or northern and southern lights, truly nature's fireworks. Earth is the only terrestrial planet to have auroras tied to its polar regions. Mars has been discovered to have auroras in its atmosphere above regions with remnant magnetism originating from the global magnetic field Mars had early in its history. Venus does not have a global magnetic field but it may also have auroras above its clouds. Observations show a structure resembling a magnetosphere that behaves like those that produce auroras on planets having global magnetic fields.
Giant gas planets like Jupiter and Saturn have auroras caused by their strong magnetic fields. For example, Saturn's magnetic field is formed deep within the planet's interior. As helium suspended higher in Saturn's interior is pulled by gravity toward its core, the interior of Saturn is heated. This heat powers convection in Saturn's interior which, in turn, powers the magnetic field.
Jupiter's magnetosphere is one of the largest features in the solar system. The plasma of electrically charged particles that exists in the magnetosphere is flattened into a large disk more than 3 million miles (4.8 million kilometers) in diameter, is coupled to the magnetic field, and rotates around Jupiter. The Galilean satellites are located in the inner regions of the magnetosphere and are subjected to intense radiation bombardment.
The intense radiation field that surrounds Jupiter is fatal to humans. If astronauts were able to approach the planet as close as the Voyager 1 spacecraft did, they would receive a dose of 400,000 rads, or roughly 1,000 times the lethal dose for humans.
Even when nearest Earth, Jupiter is still almost 400 million miles away. However, because of its size, it may rival Venus in brilliance when near. Jupiter's four large moons may be seen through field glasses moving rapidly around Jupiter and changing their positions from night to night.
Last Updated: 30 December 2013