What is the Oort Cloud?

Beyond the distant edge of our known solar system, past the realm of Jupiter and the Kuiper Belt, lies a mysterious and ancient collection of icy, planetary objects called the Oort Cloud. Not only can the component pieces (comets) from this massive cloud tell us more about the formation of our solar system and planet, but they can also pose a serious threat to life on Earth. Even though some parts of the Oort Cloud are more than 90 trillion miles away from Earth, it’s still a good idea to know what dangers lurk out there in the cosmic black!

Before we dig into the Oort Cloud’s details, perhaps we should quickly review our solar system and the surrounding neighborhood. Putting a perspective on things in space can be difficult, but it’s important to comprehend when talking about the Oort Cloud.

Distances in the Solar System

To simplify the measurement of distance in the solar system, a base variable was created to measure the mean distance between the Earth and the Sun – 1 AU. That is basically equivalent to 93 million miles. 10 AU, an increase of one order of magnitude, is the rough distance to Saturn. The range of 30-50 AU defines the Kuiper Belt, an area of comets between Neptune and Pluto. 100 AU, another order of magnitude higher, marks the edge of the heliosphere, the part of space directly affected by solar wind.


Finally, when we reach a distance of 2,000 AU, we have hit the very inner edge of the Oort Cloud. Although estimates vary, the outer edge of the Oort Cloud may stretch to 100,000-200,000 AU, roughly 180 trillion miles away from Sun.

Again, due to the vast distance from Earth, the existence and exact dimensions of the Oort Cloud are theoretical, but scientists are quite certain that it exists, due to the long history of comets that occasionally come whizzing into our inner solar system.

Where Did it Come From?

This sphere of icy debris that encircles the solar system and occasionally hurls comets into interplanetary space is truly ancient; some estimates put it somewhere around 4.5 billion years old, nearly as old as our planet. This was a time when the protoplanetary disc was still forming around the Sun, and other stars that hadn’t drifted away were likely nearby. Given that the outer edge of the Oort Cloud is roughly half the distance to our closest stellar neighbor, Alpha Centauri, many scientists believe that the Oort Cloud is a remnant from the exchange of matter that occurred during the formation of multiple stars.

When all of the Oort Cloud material was much younger, it rotated closer to the solar system’s core, but due to orbital interactions with larger gravitational objects, such as Jupiter and other gas giants, these icy objects were hurled much farther out, toward the fringes of the solar system. There, these comets have spent the majority of their lives, but occasionally, a comet is bumped out of the sphere and travels into the center of the system.

These are called long-period comets, and their orbits can reach into the thousands of years. Short-period comets originate from the Kuiper Belt, and have orbits that typically last decades, such as the legendary Halley’s Comet, which passes Earth every 76 years. The Hale-Bopp comet, which was visible for more than a year beginning in 1997, was a long-period comet that has an orbit of more than 4,200 years.

Why Does it Matter?

The Oort Cloud is important – and interesting – for a number of reasons. Firstly, due to the huge distance between the Sun and the Oort Cloud, the icy objects more than 100 trillion miles from Earth can easily be affected by other nebulae, stars and interstellar effects, which means that the Oort Cloud is constantly in flux. Thousands of comets are sent hurling towards the middle of the solar system each year, and these billion-year-old comets can give scientists a peek into the earliest days of our solar system’s formation.


The Oort Cloud is also important because if a large enough comet were to strike the Earth from the Oort Cloud, it could have absolutely devastating effects on all life forms of the planet. Therefore, monitoring long-period comets and detecting new potential dangers is crucial, not that there is much we could do if a comet the size of New York was heading straight for us.

The true challenge when it comes to learning from or theorizing about the Oort Cloud is its inaccessibility. Even Voyager 1, the most-distant man-made object in space, which has already left the heliosphere of the solar system, will not reach the outer edge of the Oort Cloud for another 300 years. Even if it did reach this ominous shell around our star, it wouldn’t be able to send back any information on what it found.

Fortunately, the next few years may prove quite illuminating in terms of studying this distant part of our solar system. Long-range space telescopes, like the James Webb Space Telescope being launched in 2018, should give us a much clearer picture of that area of space, and may provide some of the answers that this mysterious, theoretical cloud has been guarding for the past 4.5 billion years!

If you want a visual explanation of the Oort Cloud concept, take a quick look at the video below.


  1. Kuiper Belt and Oort Cloud – NASA
  2. Oort Cloud: Overview: Giant Space Bubble – NASA
  3. Oort Cloud: 10 Need-To-Know Things – NASA
  4. Oort Cloud: In Depth – NASA
  5. Oort Cloud – Northwestern Unversity
  6. Wikipedia
  7. Kuiper Belt: In Depth – NASA
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About the Author:

John Staughton is a traveling writer, editor, publisher and photographer who earned his English and Integrative Biology degrees from the University of Illinois. He is the co-founder of a literary journal, Sheriff Nottingham, and the Content Director for Stain’d Arts, an arts nonprofit based in Denver. On a perpetual journey towards the idea of home, he uses words to educate, inspire, uplift and evolve.

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