Oort cloud - Wikipedia
For thousands of years, astronomers have watched comets travel close to Earth The layout of the solar system, including the Oort Cloud, on a. Comets originate from the Oort Cloud and the Kuiper Belt. Both of these structures are positioned beyond the orbit of Neptune. The Oort Cloud. In this astronomy packet we are going to discuss the Asteroid Belt where asteroids come from, and the Kuiper Belt and Oort cloud where comets come from.The Oort Cloud and long period comets
Hillswho proposed its existence in The Hills cloud explains the continued existence of the Oort cloud after billions of years. The mass of the inner Oort cloud has not been estimated.
If analyses of comets are representative of the whole, the vast majority of Oort-cloud objects consist of ices such as watermethaneethanecarbon monoxide and hydrogen cyanide. This suggests that both originated from the original protosolar cloud,  a conclusion also supported by studies of granular size in Oort-cloud comets  and by the recent impact study of Jupiter-family comet Tempel 1. According to the models, about half of the objects scattered travel outward toward the Oort cloud, whereas a quarter are shifted inward to Jupiter's orbit, and a quarter are ejected on hyperbolic orbits.
The scattered disc might still be supplying the Oort cloud with material. According to these models, the number of collisions early in the Solar System's history was so great that most comets were destroyed before they reached the Oort cloud.
Assignment - Astronomy for Kids
Therefore, the current cumulative mass of the Oort cloud is far less than was once suspected. This explains the nearly spherical shape of the outer Oort cloud.
Recent studies have shown that the formation of the Oort cloud is broadly compatible with the hypothesis that the Solar System formed as part of an embedded cluster of — stars. These early stars likely played a role in the cloud's formation, since the number of close stellar passages within the cluster was much higher than today, leading to far more frequent perturbations.
What is the relationship between oort dust and comets?
Levison and others suggested on the basis of enhanced computer simulations that the Sun "captured comets from other stars while it was in its birth cluster. Long-period comets, such as comet Hale—Boppwhose orbits last for thousands of years, are thought to originate in the Oort cloud. The orbits within the Kuiper belt are relatively stable, and so very few comets are thought to originate there.
The scattered disc, however, is dynamically active, and is far more likely to be the place of origin for comets. Halley-family comets, named for their prototype, Halley's Cometare 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.
Based on their orbits, it is suggested they were long-period comets that were captured by the gravity of the giant planets and sent into the inner Solar System. No dynamical process are known to explain the smaller number of observed comets than Oort estimated.
Hypotheses for this discrepancy include the destruction of comets due to tidal stresses, impact or heating; the loss of all volatilesrendering some comets invisible, or the formation of a non-volatile crust on the surface.
As comets travel close to the Sun, the Sun's heat begins to vaporize the ices and causes them to form a fuzzy, luminous area of vaporized gas around the nucleus of the comet known as a coma. Outside the coma is a layer of hydrogen gas called a hydrogen halo which extends up to meters in diameter.
The solar wind then blows these gases and dust particles away from the direction of the Sun causing two tails to form. These tails always point away from the Sun as the comet travels around it. One tail is called the ion tail and is made up of gases which have been broken apart into charged molecules and ions by the radiation from the Sun. The other tail is called a dust tail and normally appears white. The dust in this tail is less strongly affected by the solar wind since the particles of dust are much larger than the ions in the ion tail.
That is why the dust tail is usually curved rather than straight, and does not point directly away from the Sun, because it is also influenced by the motion of the comet. The tails of the comet can be extremely large and my extend a distance of up to 1 AU the distance between the Earth and the Sun! It is believed to be where most of the trans-Neptunian objects are, including Pluto and several other recently discovered dwarf planets.
It is also thought to be the origin of many of the solar system's short-period comets. There are several types of Kuiper belt objects, or KBOs.
They probably moved into these irregular orbits as a result of gravitational interactions with gas giants, especially Neptune.
They are thought to be one source of short period comets. Many are in 3: These orbital resonances are relatively stable orbits, and prevent the objects being pushed out of orbit by Neptune's gravity. KBOs in a 3: