The Oort Cloud

Imagine a spherical cloud of objects, like a snowglobe after a vigorous shake. Now image that each individual particle of fake snow in the snowglobe was roughly one kilometre across, and that between each pair of fake snow particles were tens of millions of kilometres, and that there were serveral trillion particles in the globe, and you will have a rough idea of the scope of the imagined Oort Cloud.

A Look at the Oort Cloud

Sometimes referred to as the “Opik-Oort Cloud”, the Oort Cloud was first conceived by Ernst Opik in 1932 as a way of explaining the origin of long period comets. It was determined that comets are finite and eventually burn up; why, then, were there still comets after billions of years? Why had the supply of local comets, thought to be composed of material left over after the formation of the solar system, not been depleted? There must be a source of new comet material, and it is the idea behind this source that lead to the theory of the Oort Cloud. This theory was independently arrived at in 1950 by Dutch astronomer Jan Hendrik Oort, after which this hypothetical comet seed was named. Hypothetical because, as of yet, there has been no official, direct observation that the Oort Cloud actually exists, but there is a large amount of compelling theory.

Starting from the Sun a rocket would have to travel 50 AU (Astronomical Unit, or 150 million kilometres) to reach the beginning of the Oort Cloud. As much of an accomplishment that would be, that same rocket would then have to travel roughly 50,000 more AU to reach the outer reaches of the cloud.

The cloud is broken into two parts, the Inner Oort Cloud (also known as the Hills Cloud) and the Outer Oort Cloud. The Outer Cloud is spherical in shape, and starts at about 20,000 AU from the Sun. The Inner is more donut shaped and runs 50 AU to 20,000 AU. It is thought that the Inner is more strongly bound to the Sun, accounting for its shape, and the Outer much more loosely bound, allowing it to expand into a sphere.

Where Did it Come From?

The Oort Cloud is believed to be the remnants of the protoplanetary disk that formed around our own star at the beginning of the Solar System. This disk contained all the building blocks of all the planets and satellites found there.

Final Thoughts

To date, only two objects have been discovered that may be part of the Oort Cloud, and are candidates for being named OCO, or Oort Cloud Objects. Both objects have orbits that cannot be explained by the workings of the inner planets of the Solar System, and so are possibly from the Oort Cloud. Any information discovered concerning the Oort Cloud will aid in the understanding of the size and scope of our Solar System; it is believed that the edge of the cloud is roughly a quarter of the way to our nearest neighbouring star, Proxima Centauri.

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