Solar Wind

Solar Wind heading toward Earth

Facts about Solar Wind

  • The average speed of solar wind as it is radiated from the Sun is 400 km/s.
  • Pressure created by the solar wind creates the heliosphere, which extends past Pluto and into the Kuiper belt.
  • The heliosphere ends when the speed of the solar wind is subsonic, a phenomenon called termination shock.
  • The Earth’s magnetic field acts as a shield against the solar wind, protecting life on Earth.
  • Some particles in the solar wind are diverted to Earth’s polar regions, and cause the auroras in the Earth’s atmosphere.

What is Solar Wind?

Solar wind is a plasma-like emission of protons, electrons and other particles emanating from the Sun. Many of these particles have been stripped off of the elements that are within the Sun, namely hydrogen and helium.

The solar wind occurs because the Sun’s extreme heat heats up the electrons, protons and nuclei to extreme temperatures, and in doing so excites the particles such that they gain enough energy to overcome the Sun’s gravitational pull.

What is the speed of Solar Wind?

The solar wind radiates in all directions from the Sun. The speed at which solar wind is radiated differs depending on where the particles originated. The average speed of the solar wind as it is radiated from the Sun’s surface is approximately 300 – 400 kilometers per second. Coronal holes, or large regions on the Sun’s surface that are cooler than surrounding areas, eject these particles at speeds up to 800 kilometers per second.

The reason for the above differences is counterintuitive. The solar wind is actually radiated faster from cooler parts of the Sun than hotter parts of the Sun. The reason for this is that the strength of the Sun’s magnetic field over these holes is lower than the magnetic fields over the surrounding hotter areas. The charged particles radiating from the cooler areas then have less resistance to overcome on their way to the solar system.

Where does the solar wind extend to?

The pressure from the solar wind creates a shield or bubble called the heliosphere. As the solar wind begins to interact with the intergalactic medium, it loses velocity and pressure. When the velocity of the solar wind decreases to subsonic speeds, it is called termination shock. This area is called the heliopause, and is the end of the heliosphere. All of the planets in the solar system, and many kuiper belt objects reside within the heliosphere, and the oort cloud lies outside of it.

What planets does the solar wind affect?

The solar wind travels in all directions, impacting many planets within the solar system. Mercury is highly impacted by the wind. It does not have an atmosphere, but an exosphere that consists mainly of solar wind particles. If humans were to set foot on Mercury, they would quickly die from radiation without substantial protection.

Similarly, the solar wind would render Earth uninhabitable if Earth did not have an active magnetic field. This magnetic field forms a protective shield around Earth, diverting most of the particles in the wind away. A small percentage of these particles are carried to Earth’s polar regions by the magnetic fields. As these particles interact with elements in Earth’s atmosphere, they create cause beautiful light emissions known as aurora.

Most other planets within the solar system experience the same phenomena. Jupiter, Saturn, Uranus and Neptune all have aurora at their magnetic poles. Some of these auroras could possibly be seen with the human eye, but they would likely best be seen in ultraviolet part of the light spectrum. Certain moons that have atmospheres and active magnetic fields, such as Triton of Neptune, may also have small aurora caused by interactions with the solar wind.

Stellar Wind

The more appropriate name for this phenomena would actually be stellar wind, as many other stars outside of our solar system would radiate their own ‘solar winds’. Depending on the phase of the star and type of star, the solar wind may contain ions of heavier elements such as oxygen and iron.