(ORDO NEWS) — The Oort Cloud is a hypothetical region of small icy planetesimals named after Dutch astronomer Jan Oort.
The Oort Cloud surrounds the Solar System , extending probably over three light-years from the Sun , the system’s central object.
The Kuiper Belt , located beyond the orbit of Neptune, is about 1,000 times closer to the Sun than the inner region of the Oort Cloud. Below are 10 more interesting facts about this mysterious structure that you probably didn’t know about.
The Oort cloud defines the boundaries of the solar system
It is believed that the outer edge of the Oort Cloud, as it were, outlines the boundaries of the solar system and determines the limit of the Hill sphere for the Sun.
Simply put, the Hill sphere limit for the Sun (named after the American astronomer George William Hill who determined the limit) is the point at which the Sun’s gravity no longer dominates in the face of the gravitational effects of more massive bodies. In this case, these bodies will be either the Milky Way galaxy, or the gravitational effects of star clusters passing at a relatively short distance from the limit of the Hill sphere for the Sun.
The Oort cloud is the birthplace of long-period comets
Although the question of the origin (and even existence) of the Oort Cloud is still unresolved, resourceful astronomers have used data on the orbits of observed long-period comets, such as Halley’s comet, as the basis for the idea that all long-period comets, as well as “centaurs” and “Jupiter family comets” originate in the Oort Cloud.
Most short-period comets are thought to originate from a scattered disk (not part of the Oort cloud), but it is possible that they originated in the outer regions of the Oort Cloud.
The Oort Cloud is indeed very large.
Although the Oort Cloud has not been directly observed, it is thought to be like a sphere, with the inner region beginning at a distance of 2000-5000 AU. (0.03-0.08 light-years) from the Sun and extends approximately 100,000-200,000 AU. (1.58-3.16 light years) from the Sun. This is indeed a lot, considering that Proxima Centauri, the closest star to us , is only 4.2 light-years from Earth .
The Oort cloud is only five times as massive as Earth
Using sophisticated computer modeling, scientists have calculated that the Oort Cloud contains at least several trillion objects larger than one kilometer in diameter, and several billion more objects about 20 kilometers in diameter.
And this despite the fact that all these objects are on average tens of millions of kilometers away from each other. Although the total mass of the Oort Cloud is not known for certain, calculations based on the mass of Comet Halley (the supposed comet of the Oort Cloud) have suggested that the total mass of Oort Cloud objects is about 3 x 10^25 kilograms, which is about five times the mass of our planet.
The Oort cloud may contain material from other stars
The Oort Cloud is generally thought to be the remnants of a protoplanetary disk that formed the solar system about 4.6 billion years ago, but a new study has shown that the young solar system was once part of a star cluster of 200 to 400 stars. This indicates that the Oort Cloud originally formed at a great distance from the Sun and was not “bloated” during the migration of gas giants as they moved away from our star.
Moreover, improved modeling techniques show that, since the structure of the Oort Cloud is largely consistent with the idea that other stars could contribute to its formation, close encounters of stars with the Oort Cloud were much more frequent in the distant past than at present. In 2010, a team of scientists led by Harold Levison, using very sophisticated computer models, determined that about 90% of the material in the modern Oort Cloud was formed in the protoplanetary disks of other stars that were part of the cluster that once included the Sun.
The Oort cloud is very flexible
The outer edges of the Oort Cloud fall into a region where the Sun’s gravity is in direct competition with the gravitational effects of the Milky Way and star clusters. Because of this, the Oort Cloud has to constantly stretch in one direction, then shrink in the other under the influence of the tidal forces of the galactic gravitational field.
This “tug of war” is thought to be the main mechanism that knocks some objects out of their relatively stable orbits, turning them into long-period comets. The distance (100,000-200,000 AU) at which the Sun’s gravity yields to the Milky Way’s gravity is called the “tidal truncation radius.”
Stars sometimes pass through the Oort Cloud
Aside from the gravitational effects of the galactic tide, another mechanism that perturbs the Oort Cloud enough to send long-period comets into the inner Solar System is the passage of nearby stars through the Oort Cloud.
For example, a dim binary named WISE J072003.20-084651.2 (Scholz’s star) passed through the outer edges of the Oort Cloud about 70,000 years ago, but its relatively low mass and high speed minimized the effects of its passage. But the star Gliese 710 could have a major impact on the Oort Cloud, driving out a large number of comets over the next 10 million years or so.
Comets from the Oort Cloud may disappear
Shortly after Jan Oort developed a model to predict how many long-period comets from the Oort Cloud would hit the inner solar system, he noticed that far fewer comets were actually moving around than his model had predicted.
Today it is known that the number of comets that hit the outer solar system far exceeds the number of comets that hit the inner solar system. However, no known dynamic process can explain this feature; the question remains open.
Possible explanations include the destruction of comets as a result of their collisions with gas giants and their satellites, fragmentation caused by tidal stresses, or the depletion of all volatile material in the core of some comets, which would make such objects virtually invisible.
The Oort cloud contains both comets and asteroids
If what we know about the composition of known comets is representative of all comets, then most objects in the Oort Cloud will be composed of frozen water, methane, ethane, carbon monoxide, and hydrogen cyanide. However, the discovery of 1996 PW, which has an orbit similar to that of long-period comets and which has a composition and appearance similar to D-type asteroids, suggests that 1% to 2% of Oort Cloud objects are asteroids.
The Oort Cloud has never been seen
Everything we know about the Oort Cloud is based on inference, deductive reasoning, theoretical computer models, and some reasonable assumptions about the origin of long-period comets, since no one has yet observed the Cloud.
The spacecraft currently closest to the Oort Cloud is NASA’s Voyager 1 probe . Despite being one of the fastest spacecraft in history, it will take it about 300 years to reach the inner edge of the Oort Cloud and another 30,000 years to get past the outer edge.
Unfortunately, the nuclear reactors that power Voyager 1 are expected to shut down before 2030, so even if the probe does reach the Oort Cloud someday, we’ll never know.
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