1. It extends up to a light year from the Sun
The sphere of this icy cloud is thought to surround the Sun at up to a distance of 50,000 AU, making its total diameter nearly two light years. Its outer edge is a nearly quarter of the distance from the Sun to its nearest stellar neighbour, Proxima Centauri.
2. It’s where comet Hale-Bopp was born
Whereas short-term comets with orbital periods of up to 200 years, like Halley, came from the Kuiper Belt, 1997’s stunning long-period comet Hale-Bopp probably coalesced from the icy material that makes up the Oort Cloud.
3. It’s made up of trillions of icy bodies
Not including the countless smaller particles, there are several trillion icy objects with a diameter of over a kilometre making up the Oort Cloud. It’s difficult to be sure of its total mass, but it’s thought to be in the region of five times that of the Earth.
4. It’s extremely poisonous
The Oort Cloud is made up of organic ices including water, methane and ethane. It also houses carbon monoxide and hydrogen cyanide, both of which can be deadly as a gas in enclosed spaces. Ironically, hydrogen cyanide is also thought to be a precursor to the compounds that played a role in the origins of life on Earth.
5. It might be home to an undetected star
In the 1980s, physicist Richard Muller proposed a theory that the Oort Cloud could be home to a small companion star to the Sun, a brown or red dwarf. The idea was that Nemesis, as it was called, passed through part of the Oort Cloud every 26 million years, scattering particles across the Solar System and bombarding the planets with comets.
6. It was once part of the inner Solar System
When the Solar System was forming 4.5 billion years ago, the Oort Cloud was gradually coalescing over the span of the inner Solar System. It’s thought that as the gas giants moved in the outer Solar System, the object that made up the Oort Cloud were flung out to their current orbit.
7. It would take the latest spacecraft 30 years to get there
It’s technically part of the Solar System, but despite that it would still take the latest spacecraft technology 30 years to travel up to 750 billion kilometres (466 billion miles) to reach its inner edge. Currently an ideal craft for that purpose would be a Solar Sail.
8. Two dwarf planet-like objects have been discovered there
Objects of around 450 kilometres (280 miles) in diameter have been discovered in the Oort Cloud within the last ten years. One of them, Sedna, has an extreme orbital period of 11,400 years that takes it from around 76 AU to 1,000 AU away from the Sun.
0. It defines the border of the Solar System
It’s a common misconception that the orbits of the outer planets and Pluto mark the edge of the Solar System, but in fact the gravitational influence of the Sun extends much further. This is evidenced by the hold it still has on the objects in the Oort Cloud, many times that distance away.
10. It might not actually exist
The sphere of the Oort Cloud was hypothesised to exist around our Solar System and other similar planetary systems by astronomer Jan Oort in 1950. Since then, astronomers have tracked objects moving through it but are yet to make direct observations of the cloud itself.