The Oort Cloud is found on the very edge of the Solar System and houses many small icy objects. It surrounds the entire solar system in a spherical shape and is made up of two regions. We are currently unable to see the Oort cloud but through analysis of comets which came from there, scientists and astronomers have come up with many theories of what it is like.
Here are some facts on the amazing Oort cloud.
- The Oort cloud is a spherical region beyond the Kuiper Belt. It surrounds the outer edges of our solar system almost like a shell. The Oort cloud begins 100 Astronomical Units away (1 astronomical unit is the distance between Earth and the Sun) It then stretches to beyond 100,000 astronomical units away, this is trillions of miles!
- The Oort cloud is believed to have two regions. One is the outer cloud and the other is an inner disc shaped region often called Hills Cloud. This looks more like a doughnut surrounding the solar system rather than a sphere like the outer cloud.
- Within the Oort cloud are millions of icy objects made mostly from water, methane and ammonia which orbit the Sun. It is believed the objects vary widely because they came together from different parts of the universe back when the solar system was first formed. It is thought that the gravity of the Giant planets pushed these items either into the Sun, or towards the edge of the solar system, creating the Oort cloud.
- The bond between the Oort cloud and the solar system is not very strong. This makes the Oort cloud easily affected by pulls of gravity from passing stars and the milky way. This gravitational pull is what causes some of the icy objects to be thrown from the Oort cloud, into the inner solar system. When the object leaves the Oort cloud, it interacts with the Sun and becomes a comet.
- The Oort cloud and the Kuiper belt are the two areas of our solar system where comets come from. It is speculated that the amount of icy objects in the Oort cloud could be up to two trillion. The mass of these would be roughly five times the mass of planet Earth. Long term comets are more common in the Oort cloud than shorter term comets and these take over 200 years to orbit the sun. Some can take up to millions of years just to complete one orbit! Most shorter term comets can be traced back to the Kuiper belt.
- It is suspected that Halleys Comet came from the Oort cloud. This is the most famous comet of all time and is a short term comet which appears to the naked eye once every 76 years. Halley was last sighted in 1986 and is expected to reappear in July of 2061. It is thought that Halleys comet was initially a long term comet, whose orbit was thrown off and shortened by the gravitational pull of the giant planets when it travelled towards the inner solar system.
- The Oort cloud was named after Jan Oort. Jan Oort was a dutch astronomer who worked on the theory of a cloud housing icy objects when he was trying to figure out where comets come from in 1950. The theory was initially proposed almost 20 years earlier in 1932 by Ernst Opik, an Estonian astronomer.
- We have never seen the Oort cloud! Even with the amazing technology accessible to us we are yet to have a sighting of the Oort cloud. Despite this, its existence is widely accepted amongst scientists and astronomers. Due to the massive distance between Earth and the Oort cloud, it will probably be decades if not centuries before a spacecraft can get anywhere near it.