Hugh Harkins
The Oort Cloud – Solar System or Beyond?
The objective of this paper is to stimulate thinking on our current understanding of the theorised Oort Cloud (this has not been directly observed) as defined in relation to our Solar System.
The current size or boundaries of the Solar System cannot be easily determined. There are several regions that have been put forward as the appropriate boundary of the Solar System – the Termination Shock and the Heliopause (contained within the Heliosheath) or even the Bow Shock, beyond which is the realm of the Inter Stellar Medium (accepted as the region(s) of space over which no single star has dominance). The physical characteristic that currently define the boundary of the Solar System are generally considered to be the effective influence of the solar wind. However, considerably well beyond the obvious dominant effects of the solar wind can be found the region of space termed the Oort Cloud. As currently theorised, this is a region of icy bodies (Comets) that are shrouded around the Solar System like a vast sphere.
Whilst the Oort Cloud would be positioned at vast distances beyond what is currently accepted as the boundary of the Solar System, the objects within it predominantly come under the gravitational influence of The Sun, which they orbit in concert with other objects in the Solar System. Oort Cloud bodies take thousands to hundreds of thousands of years to complete a single solar revolution.
In line with available scientific evidence the paper recommends that the accepted boundary of our own Solar System should be reconsidered in light of scientific data that has emerged in recent decades. The Solar System boundary should extend out to the outer Oort Cloud, currently defined as being in the realm of the Inter Stellar Medium.
Figure 1 shows distances in AU (1 AU = 1 x the distance from the Sun to the Earth (~93 million miles)) for major Solar System bodies/boundaries, out to the Oort Cloud and beyond to the nearest extrasolar Star system, α-Centauri at 1,000,000 AU. The graphic shows the Voyager 1 spacecraft crossing into the Interstellar Medium at ~100 AU, some 900 AU before expected first encounter with the Oort Cloud at 1,000 AU. Estimated timeframe for Voyager 1 to reach and cross the Oort Cloud is 300 years and ~30,000 years respectively (NASA).
The physical characteristic that currently defines the boundary of the Solar System is generally considered to be the effective influence of the Solar Wind – a high speed flow of particles, mainly protons and electrons. The Solar Wind emanates from the Sun, continuing through the Heliopause to the Bow Shock, at which point it can be turned back on itself (Green & Jones, 2015). This, therefore, has proved a convenient region to designate as the boundary of our Solar System and the start of interstellar space.
At vast distances, beyond the obvious dominant effects of the Solar Wind can be found the region of space termed the Oort Cloud. As currently theorised (the existence of the Oort Cloud has not been confirmed through observation and remains theoretical, put forward by Dutch Astronomer Jan Oort whom predicted its existence in 1950) is a region of icy bodies (Comets) shrouded around the Solar System like a vast sphere. These icy bodies move with the Sun within the Milky Way galaxy (Hanse et al, 2017 & Green & Jones, 2015).
Figure 2 shows several potential boundaries of the Solar System with the Sun at its centre. The Termination Shock (with tracks of the two Voyager spacecraft), Heliopause (the boundary of the Heliosheath) and the Bow Shock (NASA).
Figure 3 shows the Oort Cloud, positioned at vast distances beyond what is currently accepted as the boundary of the Solar System, with the Solar System out to the Kuiper Belt (region of trans-Neptunian objects that include Pluto). Figure 4 depicts the Voyager 1 spacecraft entering Interstellar Space at around 100 AU (NASA).
The Suns gravitational pull has considerable influence on Oort Cloud bodies, considerably beyond the obvious effects of the Solar Wind. This gravitational influence is so great that Oort Cloud bodies are pulled into orbit around the Sun.
It is recommend that the accepted boundary of our Solar System be reconsidered as evidence supports the case for the Solar System boundary extending to the outer Oort Cloud, currently defined as being in the realm of the ISM. Additional research is required into the effects/reach of the Solar Wind, the Suns gravitational effects on Oort Cloud bodies and on efforts to observe the Oort Cloud, directly or indirectly, in order to confirm its existence.
Regardless of whether or not it is defined as being in Interstellar Space or an integral region of our Solar System, the Voyager 1 spacecraft will not reach the Oort Cloud for around 300 years, emerging from the other side ~30,000 years distant.