Oort cloud
The Grand Storehouse Of Comets
Moons, planets, and every such celestial body in space has a reason for its existence. The moons of Saturn or Neptune’s moon did not come around the planet from the thin air. They’d have originated somewhere else and might have been captured via gravity. In a similar manner, the periodic motion of comets (eg. Halleys Comet, Barnard, Olmert, etc), their common properties, and eccentricities point at the presence of a phenomenon that has been taking place at a grand scale.
Let’s explore it further….
What is Oort cloud?
Oort cloud is a hypothetical spherical structure like kuiper belt( donut-shaped) that contain comets, asteroids, and debris.
Unlike the orbits of the planets and the Kuiper Belt, which lie mostly in the same flat disk around the Sun, the Oort Cloud is believed to be a giant spherical shell surrounding the rest of the solar system.
A.O Leuschner talked about elliptical orbits. In the year 1932, Ernst Öpik postulated the long-period comets( it has been explained below) might come from a distant place from where they originated. He suggested the presence of this region at the outer edges of the solar system.
Jan Oort tried to resolve the problem. He noted a peak in the numbers of long-period comets with aphelic( their farthest distance from sun) pointing at the presence of a reservoir at that distance.
Origin
A protoplanetary disk is a rotating disc around a young star. The disk is composed of dense gases and dust. The formation of planets began more than 4 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. The Oort cloud is believed to have formed at this time from the protoplanetary disk.
Astronomers believe that the outer Oort cloud has little effect on the solar system and is easily affected by the gravitational attraction of other bodies. Sometimes due to the effects of gravitational attraction, the comets move toward the inner region.
Just as moon’s tidal force effects the earth’s oceans, in a similar manner, it is believed that the galactic tide also has a profound effect on the orbits of bodies in the outer solar system due to sun’s weak gravity. When we take this concept ahead, we find that the comets are under the influence of forces which are in the nearby proximity and the others which are having an influence from a distant place.
Based upon this, we have two classes of comets — ecliptic and isotropic. Both of these can be differentiated on the basis of their period. The short-period comets are termed as ecliptic and long-period ones are called isotropic. The ecliptic comets having a short-period trace their origin from the kuiper belt. On the contrary, the isotropic comets are said to trace their origin from a hypothetical structure called Oort cloud. There are two main varieties of short-period comet: Jupiter-family comets and Halley-family comets. Halley-family comets, of which Halley’s Comet is a prototype, are unusual in that although they are short-period comets, it is hypothesized that their ultimate origin lies in the Oort cloud, not in the scattered disc.
Now as moon’s tidal force effects earth’s oceans, in a similar manner, it is believed that the galactic tide also has a profound effect on the orbits of bodies in the outer solar system due to sun’s weak gravity. What is a galactic tide? — Well, it’s a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Some astronomers predict that the galactic tidal forces’ effects can shift orbits in Oort cloud to bring objects closer to sun. Scientists predict that the galactic tide was responsible for the formation of the Oort cloud.
You might be thinking why it has not been discovered yet.— Well, first of all, no direct missions have been commissioned to explore the Oort Cloud yet. Secondly, the five spacecrafts will eventually get there but without fuel because of distance. They are Voyager 1 and 2, New Horizons, and Pioneer 10 and 11.
Voyagers are the artificial objects sent fastest and farthest away by the humans. These objects have proved themselves to be the greatest demystifiers. They have fetched as much information as possible. The present distance of Voyager-1 from earth is approximately 14 billion miles. But still being so far it hasn’t been able to reach the Oort cloud. Now, you can imagine the distance of Oort cloud from our earth( in case it exists). For Voyager, it will reach the Oort cloud in about 300 years and would take about 30,000 years to pass through it. Unfortunately, Voyager-1, has the hydrazine that can last till 2039–40. Even its RTGs won’t work till then. Its fuel won’t last for so long. Scientists have already shut down many instruments to keep them working longer. So with Voyager we don’t see a chance of witnessing the presence of Oort cloud. Possibly, we’ll need some other instrument or spacecraft.
Sedna, a dwarf planet in the outer reaches of the solar system, and one of the largest in the solar system is a long period comet. It is at 31 times Neptune’s distance from sun. Astronomers refer it to as the first known member of the Oort cloud. Sedna will be near to us at perihelion around July 2076. The close approach to the Sun provides an opportunity for the study that will not occur again for 12,000 years. Based upon the calculations, it was suggested that a flyby mission to Sedna could take around 25 years using a Jupiter gravity assist. With time and technological development we’ll certainly witness the objects and events that are presently beyond our reach….
