The Oort cloud, Source of Long-Period Comets

The Oort cloud is a massive spherical shell composed of icy objects orbiting the sun beyond the orbit of Neptune. It is extremely distant and stretches over a large area extending towards the edge of the solar system and reaching  almost halfway to the stars nearest to the solar system.

The Oort cloudThe Oort cloud Image Source: NASA

What is The Most Interesting Fact about the Oort cloud?

Astronomers are fascinated by the Oort cloud because they believe it is the source of long-period comets that sometimes enter the inner solar system. This area is also believed to be composed of remnants of the early solar system. Astronomers want to study its composition to learn more about the formation of the solar system. It remains a mystery because its existence is only a hypothesis and has not been proved. Here are some of the interesting facts about this cloud.

Why Is It Called the Oort cloud?

The Oort cloud was named after Jan Oort, a Dutch Astronomer who predicted its existence. He predicted its existence after studying the orbit of comets. He proposed that some of the comets entering the solar system originated from a cloud of icy objects.

Jan Oort

 Jan Oort Image Source

How Far Away Is the Oort cloud?

Brian Marsden computed that the Oort cloud is located between 40,000 and 50,000 astronomical units (AU) from the sun. (1 AU=150 million km/93 million miles).

There are differing beliefs on how far the Oort cloud is. Some astronomers believe that it starts at 2000 or 5000AU and stretch up to 50,000 AU while others believe that it stretches up to 100,000 AU. It is too far away to be seen clearly even with a telescope. Its objects are also too small.

The Origin of the Oort cloud

Scientists believe that the objects in the Oort cloud formed near the sun during the formation of the solar system. The gravitational force of the planets scattered away these objects, which settled into the far edges of the solar system forming the Oort cloud.

How Do We Know That the Oort cloud Exists?

The Oort cloud has not been observed and there is no direct proof that it exists. However, scientists strongly believe that it does exist and accounts for a significant fraction of the total mass of the entire solar system.

Only a few objects have been identified as having come from this region including the comet Hale-Bopp that flew from the Oort cloud passed near earth and went back to the Oort cloud. It was visible for one year and a half.

The Comet Hale-Bopp

The Comet Hale-Bopp Image Source

The Oort cloud Contents

The Oort cloud is composed of icy bodies consisting of ammonia, water and methane. Trillions of objects are found in this area. These are also referred to as Trans- Neptunian Objects because they orbit the sun beyond the orbit of Neptune.

Long-period comets that take at least 200 years to orbit the sun are believed to originate from here. Other objects believed to come from this region include Halley-type comets, centaurs and Jupiter-family comets. Identified objects from this region include Sedna the dwarf planet, 2006 SQ372, 2008 KV42, and 2000 CR105.

These are a few exceptions, such as when Halley ’s Comet a short-lived comet came from the Oort cloud. The comets are spread apart within this cloud.

The outer extent is in an area where the gravitational influence of the sun is weak and that of nearby stars strong. Sometimes clouds, passing stars and tidal interactions with the milk way disc disturb  the orbit of some comets and send  them to the inner solar system or farther into interstellar space. Short period comets take less than 200 years to orbit the sun and are believed to come from the Kuiper Belt.

Icy Objects Orbiting the Sun in the Oort cloud

Icy Objects Orbiting the Sun in the Oort cloud Image source

How Big Is the Oort cloud?

The Oort cloud is believed to be made up of matter 40 times that of earth.  It is believed to have two regions, an outer region that is spherical and an inner region that is disc-shaped and also known as Hills cloud.

Is There a Planned Mission to Explore the Oort cloud?

The Oort cloud is so far away that no mission has ever been made to the Oort cloud. Still, not much is known about this region to plan a mission. There is no planned mission to explore this area in the near future. NASA’s New Horizons will only reach and explore the Kuiper Belt and some of its objects.