(ORDO NEWS) — The Oort Cloud is a hypothetical region of small icy planetesimals named after the Dutch astronomer Jan Oort.
The Oort Cloud surrounds the solar system , extending probably more than three light-years from the sun , the central object of the system. The Kuiper Belt , located beyond the orbit of Neptune, is about 1000 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 delineates the boundaries of the solar system and defines the limit of the Hill’s sphere for the sun. Simply put, the Hill’s sphere limit for the Sun (named after American astronomer George William Hill who defined this 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 small distance from the Hill’s sphere limit for the Sun.
The Oort cloud is home to long-period comets
Although the question of the origin (and even the existence) of the Oort Cloud is still unclear, resourceful astronomers have used the data on the orbits of observed long-period comets, such as Halley’s comet, as a basis for forming the idea that all long-period comets, as well as “centaurs” and the “Jupiter family comets” originate in the Oort Cloud.
Most short-period comets are believed to originate from a scattered disk (not part of the Oort cloud), but it is possible that they originally originated in the outer regions of the Oort Cloud.
The Oort cloud is really very large
Although the Oort cloud was not directly observed, it is believed to be similar to a sphere, the inner region of which begins 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 more massive than Earth
Using sophisticated computer simulations, scientists estimate that the Oort Cloud contains at least several trillion objects with a diameter greater than one kilometer, and several billion more objects with a diameter of about 20 kilometers.
And this despite the fact that all these objects are, on average, tens of millions of kilometers from each other. Although the total mass of the Oort Cloud is not known for certain, calculations based on the mass of Halley’s comet (the putative 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
It is believed that the Oort Cloud is the remnant of the protoplanetary disk from which the solar system formed about 4.6 billion years ago, but new research has shown that the young solar system was once part of a star cluster of 200-400 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 because the structure of the Oort Cloud is largely consistent with the idea that other stars may have contributed 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 highly sophisticated computer models, found that about 90% of the material in today’s 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 boundaries of the Oort Cloud fall into an area 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 contract in another under the action of the tidal forces of the galactic gravitational field.
This tug of war is believed 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
In addition to the gravitational effects of 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 faint binary called 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 velocity minimized the effects of its passage. Gliese 710, on the other hand, could have a major impact on the Oort Cloud, displacing large numbers of comets over the next 10 million years or so.
Comets from the Oort Cloud may disappear
Soon after Ian Oort developed a model predicting how many long-period comets from the Oort Cloud would enter the inner solar system, he noticed that far fewer comets were actually moving than his model predicted.
Today it is known that the number of comets that enter the outer solar system far exceeds the number of comets that enter 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 render such objects almost invisible.
The Oort cloud contains both comets and asteroids
If what we know about the composition of known comets is considered representative of all comets, then most objects in the Oort Cloud will consist 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 has a composition and appearance similar to D-type asteroids, suggests that 1% to 2% of Oort Cloud objects are asteroids.
No one has seen the Oort cloud yet
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 about 300 years for it to reach the inner edge of the Oort Cloud and another 30,000 years to pass the outer edge.
Unfortunately, the nuclear reactors that power Voyager 1 are expected to shut down by 2030, so even if the probe does ever reach the Oort Cloud, we will never know.
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