A Discussion on Interstellar Pickup Ions

Although there is a lot known about the physics that dictates the movement of the planets and starts throughout the night sky, little is known about the medium which encompasses these heavenly bodies. Let us consider our own solar system as an example of this. The reason for the orbit of planets around the Sun has been well known for quite some time. In addition to this, the predictability of these motions is represented well with the assistance of Einstein's theory of General Relativity. However, as technological advancements in science have given us the ability to send spacecraft to the farthest reaches of our solar system, scientists have come to discover that there are many physical phenomenon's that are unexplained. An example of this is the solar wind. Since the Sun is the source of this highly energetic and multifaceted medium, we must also observe and study it closely in order to better understand the medium that it produces. The solar wind is an expanding gas composed mostly of protons and electrons moving radially away from the solar source. It expands at high speed, roughly ten times the speed of sound, to form a high Mach number flow. As the solar wind expands outward, the speed remains constant and the density decreases. Table 1 is an example of solar wind parameters consisting of velocity, density, temperatures, etc. observed at different radial distances from the Sun. There are other additional factors which complicate the radial movement of the solar wind. One of them is the magnetic field that the Sun generates, and the other is the Suns rotation. As you may or may not know, the Sun is a moderately static body with an intrinsic rotation about an axis, just like the Earth. Due to this rotation, the solar wind ejected from the Sun will travel in a radial and azimuthal fashion. In addition, the solar wind is largely comprised of charged particles. This forces the Suns magnetic field to be stretched in a spiral fashion. The theory of the solar wind spiral motion was first developed in 1958 by the space plasma physicist Eugene Parker [2][3][4]. Due to his discovery, we now refer to this behavior as the Parker spiral. Figure 1 is an example of the Parker spiral and the current sheets that are subject to its existence. As previously stated, the expanding solar wind carries with it an …