Oort Cloud


Much of the information about the Oort Cloud is theoretical, but it is believed to be a bubble of thick, icy debris that surrounds the outside of our entire solar system.

It is thought that the Oort Cloud may extend 1/3 of the distance between our sun and the next star, which is around 1,000 and 100,000 AU (astronomical units). To give you an idea of how far that is, our Earth is one AU from the sun, which is around 93 million mi/150 million km.

Oort Cloud

The cosmographical boundary of the solar system is defined by the edge of the dominance of the sun’s gravitational influence, and the outer limit of the Oort Cloud is the final portion of that boundary.

The Oort Cloud is the most outer boundary of what we consider to be part of our solar system. Some theorize that the contents of the Oort Cloud may have originated in the Kuiper Belt but over time, became scattered as they were captured by the gravitational pull of the gas giants.

Oort Cloud Statistics:

The Oort Cloud may contain hundreds of billions to possibly even trillions of icy bodies. The cloud expands out to almost ¼ of the distance to our nearest star, Proxima Centauri. It consists of an outer cloud and an inner donut-shaped cloud called a “torus.”

Scientists believe that the contents of the Oort Cloud is where many of the comets originate from. Whenever any of the bodies within the Oort Cloud crash into each other or experience a disturbance of some kind it can knock them out of the Oort Cloud into a trajectory that heads to the sun.

There are two examples of this in more recent years: C/2012 S1 (ISON), which was destroyed when it got too close to the sun, and C/2013 A1 Siding Spring, which passed closed to Mars and will return to the solar system in 740,000 years.

The Oort Cloud exists far beyond the farthest edges of the Kuiper Belt and well beyond the dwarf plant Pluto.

It’s important to note that although the planets in our solar system orbit on in a flat plane, the Oort Cloud is thought of as a huge spherically-shaped shell that surrounds the sun, planets, and the objects in the Kuiper Belt. Objects in the Oort Cloud can be of all sizes including some that are mountain-sized or larger.

Scientists are unsure of the exact mass of the Oort Cloud, however, they have used Halley’s Comet as a kind of example to configure an estimated mass of 3 x 1025 kg which is nearly 5 times the total mass of Earth.

History of the Name:

Although the first suggestion that the cloud might exist originated in 1932 from an Estonian astronomer, Ernst Öpik, it was in 1950 that Jan Oort, a Dutch astronomer proposed the possibility of a sphere if icy bodies in the great expanse of the solar system.

He believed that this feature would explain the location of how comets originated and why it takes them thousands of years to orbit the sun. These are referred to as “long-period comets,” and most of them are only seen once in recorded history.

The comets that make more frequent appearances are called “short-period comets.” The Oort Cloud was named for Jan Oort and is also referred to as the Öpik-Oort cloud.


It’s believed that the Oort Cloud contains the remains of the disc materials that originally formed the sun and planets in our solar system around 4.5 billion years ago.

Scientific theories indicate that the matter that is contained in the Oort Cloud was scattered out due to the intense gravity of the gas giant planets early in the history of the evolution of our solar system.

The Oort Cloud is considered to be loosely bound to our solar system which also means that they can be influenced by the gravitati0onal pull from both passing stars and the Milky Way galaxy.

Interesting Information:

Objects in the Oort Cloud are constantly changing. Sometimes there are objects that have an interaction such as crashing into another object or veering too close to become influenced by another object’s gravitational pull.

The interaction causes the population of the Oort Cloud to get new members when the sun captures passing objects as well as kick those out that are involved in collisions.

The comets that originate in the Oort Cloud can travel incredible distances, often as much as three light-years from the sun. The important thing to understand about comets is that the farther they travel the less they are held by the sun’s gravitational pull.


This means that they can be influenced by passing stars or molecular gas clouds and change the orbit of the comets. An orbit change can remove them entirely or even throw them back towards our sun.

Studying comets is one way that scientists can get more information about the Oort Cloud, but comets are really difficult to study.

Some comets can take over 200 years to complete a revolution and they spend a lot of their time in the outer solar system areas.

These long-period comets never get close enough to the sun or our ability to view them in a single lifetime. Some long-period comets have travel orbits that can last thousands or even millions of years.

Our sophisticated and high-tech telescopes give us the ability to see far distant galaxies, however, we are still unable to see the smaller, closer objects that are in the Oort Cloud.

The Oort Cloud objects are very faint, even with the power of the Janes Webb Telescope. In order to view the Oort Cloud objects, our telescopes are required to be 100 billion times stronger.

We haven’t had any close-up research for the Oort Cloud, so many of the ideas are still theories and astronomers continue to debate them. One of the theories that many agree on is that in observing long-period comets such as Halley’s Comet, they believe that they can use them as a base to confirm that they could have originated in the Oort Cloud.

This has led scientists to theorize that other long-period objects, including Jupiter-family comets and centaurs could also have originated in the Oort Cloud.

The objects known as the short-period comets are believed to have originated in the scattered disc, an area outside of the Oort Cloud, although scientists are open to the idea that some may have started as part of the Oort Cloud.

Oort Cloud Comet-Specific Information

Direct observation of the Oort Cloud hasn’t been possible, so many of the concepts that astronomers have are theoretical. One idea is that the appearance of the Oort Cloud is like a spherical ball, and that the thick walls of the Oort Cloud are from 2,000-5,000 AU (0.03-0.08 light years).

Scientists have made use of computer models to estimate the huge size of the Oort Cloud and think that there may be as many as several trillion objects in the Oort Cloud that are larger than 1 km in diameter, with another several billion that are of other sizes.

Oort-cloud comet

In 1996, comet Hyakutake passed Earth within 9 million mi/15 million km as it was finishing its 17,000 year journey from the farthest reaches of the Oort Cloud.

Another long-period comet that astronomers had an opportunity to view was the Hale-Bopp comet, which was visible for study for 1 ½ years as it passed within 122 mi/17 million km of Earth.

Each of the orbits of these long-period comets was drastically changed due to their passing through the solar system. While it is now considered to be a Kuiper Belt object, it’s thought that the well-known Halley’s Comet originated in the Oort Cloud.

Oort Cloud Other Objects:

The Oort Cloud contains objects that vary in size to include the very large. Scientists have identified quite a few dwarf planets that they believe have been part of the Oort Cloud group.

The biggest of the dwarf planets is Sedna, whose size is around ¾ of that of Pluto. Sedna’s distance from Earth is 8 billion mi/13 billion km, and it has an orbit around the sun that takes 10,500 years.

Additional Oort Cloud objects have included comets with a range of 30-155 mi/50-250 km in size and include: 2006 SQ372, 2008 KV42, 2000 CR105 and 2012 VP113.

The most recently discovered addition to this group is nicknamed “The Goblin”. Officially known as 2015 TG387, research about it was published in 2018.

Space Visits:

  • The Oort Cloud is way too far at the end of the solar system for us to visit as of yet. In 1977, NASA launched the Voyager 1 and it travels at a million miles each day. Even at that speed, it will take Voyager 1 around 300 years to reach the Oort Cloud inner layer and an additional 30,000 years to reach the far side of the thick Oort Cloud.
  • NASA’s WISE spacecraft uses infrared wavelengths to scan our skies. Using the data from WISE, astronomers have discovered that there are around seven times more long-period comets that measure 0.6 mi/1 km across than they previously thought. Scientists also found that long-period comets have an average size that is twice as big as “Jupiter family comets,” whose orbits are affected by the gravity of Jupiter and are less than 20 years. Astronomers have established a theory by using the WISE observations that these long-period comets were more than likely kicked out of the Oort Cloud millions of years ago.

Oort Cloud Facts for Kids:

  • Estimates using scientific models show that the Hills Cloud has 10-100 times more comet objects as compared to the outer Oort Cloud.
  • Trans-Neptunian objects (TNO) is the term used to relate to all objects that exist outside of the orbit of Neptune, including the Kuiper Belt and the Oort Cloud contents.
  • As we continue to study our solar system, scientists believe that in the early time of the formation of the sun’s nebula, the sun’s gravity snagged material from other stars and outer discs to form the Oort Cloud.
  • The Oort Cloud is divided into two specific regions: the outer spherical and the inner Hills cloud that has a disc-shape.
  • Objects in the Oort Cloud are mostly made up of water ice, methane, and ammonia.
  • Scientists that study long-period comets, whose paths of orbit are 200 years or more, believe that they originated within the Oort Cloud.
  • The 2003 discovery of Sedna, a planetoid also called 90377, promoted scientists to believe that it was thought to have originated from the inner Oort Cloud.
  • It’s believed that there are 2 trillion objects in the Oort Cloud.
  • The term “absolute magnitude” is the measure of the intrinsic brightness of celestial objects. Scientists assume that there may be several billion objects that exist in the outer halo that have an absolute magnitude that is brighter than 11.
  • As astronomers continue to learn more about the Oort Cloud their studies have shown that they believe the Oort Cloud reached its peak around 800 million years ago after it was formed. However, as objects are involved in collisions, the Oort Cloud mass has gradually been reduced due to the fact that the depletion rate is larger than the rate that it has in grabbing other objects and replacing them.
  • In 2010, Harold F. Levison used advanced computer simulations to propose that during its birth phases from the protoplanetary discs, the sun actually captured comets of other stars. The proposal indicated that more than 90% of the Oort Cloud objects are from other stars and the balance is from our sun’s own protoplanetary disc.