The Oort cloud around our solar system
Recent astronomical discoveries reveal a fascinating structure within our solar system. It consists of three zones. (Four if you also consider the Sun as a zone.) It is in the center of the Sun surrounded by a zone of four ‘Earth-like’ planets. These are the planets Mercury, Venus, Earth and Mars, which all consist of a dense, rocky substance. Around it is the asteroid belt; a disk with rocks of various sizes. Outside the zone are the so-called ‘Gas Giants’: Jupiter, Saturn, Uranus and Neptune. (Giant planets with relatively sparse composition.) Their territory is again surrounded by the Kuiper Belt; a huge disc consisting of chunks of frozen gas. Some of these pieces have a planetary shape such as the dwarf planet, Pluto. Finally; the last zone, a thousand times larger than the zones mentioned above, the Oort Cloud.
The Oort Cloud
This hypothetical gas giant is a spherical cloud of comets surrounding our solar system. Its outer edge is about 50,000 astronomical units from the Sun. That is about 0.79 light years. (A light-year is the distance traveled by light in one year.) The Oort Cloud travels the Astronomical Unit; the distance between the Sun and Earth. That is about 150 million kilometers.
The Kuiper Belt and scattered disc, two other reservoirs of TNCs (Trans-Neptunian Objects) within our solar system are, compared to the Sun, only one thousandth of the distance from the edge of the Oort cloud. The outer limit of the Oort cloud defines the cosmographic boundary of our solar system. This is the area which dominates the gravitational force of the Sun. Objects that this space will slowly be pulled towards the Sun and eventually end up in this area. In orbit, an object to a neighboring star or gas cloud will be drawn outside the area.
Constitution of Oort Cloud
It is thought that the Oort cloud consists of two parts. A spherical outer cloud and a donut-shaped disk or inner cloud. The latter is also called “Hill Cloud”. The objects in the Oort cloud consist largely of ices such as Water, Ammonia and Methane. Astronomers believe that the matter inside the Oort cloud originally formed closer to the Sun. However; it was forced apart by the gravity of the four giant planets orbiting around the Sun during the evolution of the solar system.
Origin of Comets
So far, there aren’t any direct observations of the Oort cloud. Nevertheless, many astronomers believe that it is the origin of many Halley-type comets. These are comets that can occur anywhere in the sky unlike Jupiter Family comets or former Centaurs. They are always seen on a path from the Sun to the Earth. Both the Oort comets, like the Jupiter Comets, probably arose from the original protosolar (disc-shaped) cloud. This came about 4.6 billion years ago.
There were four bodies discovered far beyond the Kuiper belt that might belong to the Oort Cloud. Only one of them has received a name. That is the dwarf planet Sedna, named after an Eskimo (Inuit) goddess. Sedna’s presence suggests an inner, donut-shaped disk in the plane of the Ecliptic. That is the imaginary path that all planets and other celestial bodies (other than Halley-type comets) orbit the Sun. The existence of the stable Hill Cloud may explain the lasting stability of the highly volatile and tenuous Oort cloud after billions of years.
Estimated Mass of the Oort Cloud
The estimated mass of the billions of objects in the Oort cloud is about five times the mass of Earth. In kilos that are a 3…followed by 25 zeros! It was previously thought to be about 380 Earth masses, but the increased knowledge about comets is significantly revised downwards.