13May2013

What Is The Solar Wind?

An image of the Solar Wind and What the Earth’s Magnetosphere

The solar wind? What is it? It is a charged stream of particles released form the upper atmosphere of the sun. These particles escape the sun’s gravity through kinetic energy.

The  high temperatures of the corona (the outer atmosphere) allow this to happen. Solar wind creates the heliosphere, the huge bubble in interstellar space. The heliopshere surrounds the entire solar system. Solar wind also creates geomagnetic storms, aurora (known as the northern and southern lights), and plasma tails of comets. Solar wind in a nutshell is plasma.

We will not get into the most detailed aspects of solar wind, what it is, what it does, how it affects every planet in the solar system. What we will try to do here is break it down and make it fairly easy to understand.

First of all, it moves through space not like wind at all; it is rotated by the influence of the rotating magnetic field of the sun. We refer to this as the heliospheric current sheet. It spins from the center outward, like a ballerina’s skirt. It continues to move outward into interstellar space at speeds of 1-2 million mph. Solar wind is constantly released from the sun in all directions. Solar wind is also responsible for the overall shape of Earth’s magnetosphere. There is a bow shock as it approaches the magnetosphere. This upstream from the bow shock wave exposes geostationary satellites to solar wind. This in turn is what we call space weather, which is also flares, prominences and coronal mass ejections.

Magnetospheres and Intrinsic Magnetic Fields

There are planets that have interplanetary magnetic field, like Earth does, both internal and external. Then there are planets that have intrinsic magnetic fields, which are little to no geomagnetic fields. Mercury, for instance, has an intrinsic magnetic field, but its atmosphere has been stripped because it takes the brunt of the solar being so close to the sun its surface is vestigial and is always bathed in radiation.

solar winds

solar winds (Photo credit: alandberning)

Venus, has an atmosphere that is 100 times denser than Earth’s atmosphere, but has a weak geomagnetic field. Even though it is weak, space probes have found Venus’s geomagnetic field extends like a comet tail to Earth’s orbit.

Even though the Earth is largely protected by the magnetic field and the magnetosphere, some charged particles get trapped in the Van Allen Radiation Belts and a small amount gets into the Ionosphere where the auroral zones are located. Bright auroras strongly heat the Ionosphere.

Mars is rather far from the sun but yet the solar wind has stripped away a third of its original atmosphere, leaving a layer 1/100th as thick as Earth’s. It is believed that this atmospheric stripping is a gas being caught in bubbles of the magnetic field, which are stripped by the solar wind. Earth’s moon has no atmosphere or intrinsic magnetic field and is constantly bathed in solar wind and radiation and gets no protection from Earth’s magnetosphere.

 By AccuWeather Astronomy expert Julianne Troutman.