Oort Cloud Facts | Diameter, Dimension & More

The Oort cloud is one of the most mysterious parts of our solar system. There’s still a lot we don’t know about it, which makes it the subject of many debates within the astronomy society. Fortunately, we think we know more about it know than we did just a few decades ago.

Although the Oort cloud isn’t actually physically proven to be existent, many astronomers believe that it is legitimate. The Oort cloud is so far away that we cannot see it from Earth, and it can only be seen with a space vessel.


The Oort cloud is out beyond the Kuiper belt, and goes right out to the edges of our Solar System. This means that whilst it is affected by the gravity of the Sun, it’s also affected heavily by other objects and actually from the Milky Way.

How big is the Oort cloud?

One of the most common questions about the Oort cloud is about it’s size. Just how big is it, exactly? Well, the best way to explain this would probably be via this image which compares the Oort cloud to the size of the Kuiper belt. Remember that the Kuiper belt is a large donut shaped belt beyond where any of our main planets exist, and home to dwarf planets like Pluto and Eris.

With the Kuiper belt being between 30-50 AU in thickness from the Sun, it’s very easy to see just how big the Oort cloud is. The Oort cloud is the last thing between us and interstellar space.

Oort Cloud Facts

  1. The Oort cloud takes it’s name from astronomer Jan Oort, who proposed the idea of a cloud all the way back in 1950. However, other astronomers had theorized it’s existence earlier than this, including Estonian astronomer Ernst Opik, all the way back in 1932.
  2. The inner part of the Oort cloud is around 185 BILLION miles (300 billion km) away from the Sun.
  3. Although we aren’t sure on the number of objects in the Oort cloud, we generally think that there are at least a few trillion different objects out there.
  4. We generally split the Oort cloud into two different parts. Firstly, you have the spherical outer Oort cloud. But, you also have a donut shaped inner cloud, too.
  5. The most well known object that we believe to be in the Oort cloud is named Sedna. It is 3x the distance that Neptune is from the Sun, and is thought to be towards the edges of our Solar System.
  6. We don’t know the total mass of the objects in the Oort cloud, but we think that it is probably around 5x that of the mass of Earth.
  7. We think that the Oort cloud was probably formed at the same time as the planets, and the objects were forced out there by gravitational interactions with planets in our solar system.

Most Commonly Asked Questions about Oort Cloud

Where is the Oort cloud?

The Oort cloud is further out towards the edges of our solar system, past Neptune and even past the Kuiper belt.

Why is the Oort cloud spherical?

The first thing to realise about the Oort cloud is it’s distance from the Sun – it’s hundreds of billions of miles away, so the Sun’s gravitational affect on the objects on the Oort cloud is minimal. Because of it’s distance from the Sun, it’s likely that it is a spherical shape caused by the galactic tides of the Milky Way.

Do comets come from the Oort cloud?

One of the reasons why astronomers are so sure that the Oort cloud exists is because of comets – we think that many comets actually originate in the Oort cloud. These long-period comets are thought to essentially come from the Oort cloud, and get sucked in by the Sun’s gravity, where they die.

Has the Oort cloud been proven?

Although the Oort cloud was theorized many decades ago, it is still an impossibility to know for sure whether it really exists or not. However, the majority of astronomers believe that the Oort cloud is out there, so we generally think of it as being real.

Will Voyager 1 or 2 make it to the Oort cloud?

Whilst Voyager 1 and 2 have both made it beyond the heliosphere, it’s estimated that it would still take hundreds of years to reach the Oort cloud from this point.


Overall, it’s pretty clear to see that the Oort cloud is one of the most intriguing things within our solar system, as well as being one of the things we know the least about! Trillions of objects made from ice, methane and ammonia are thought to exist out in the Oort cloud, but it is unlikely we will find a way to observe things out there any time soon and prove it’s existence.

If you have any Oort cloud questions, then please leave a comment below and I’ll try to answer it the best that I can!

About Alan

I'm Alan, and I'm the owner of Odyssey Magazine. My dad bought me my first telescope as a teenager, and I've been obsessed with the universe ever since. We created this resource to try and help kids and adults learn more about astronomy!


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