When we visualize the solar system, we usually think of the Sun, the eight orbital planets, and perhaps the icy dwarf planet Pluto. But gravitational mechanics suggest that our Sun’s empire stretches vastly further into the cold, black void. Welcome to the final frontier: the Oort Cloud.
A Theoretical Spherical Shell
The Oort Cloud is not a flat ring of asteroids like the main Asteroid Belt. Instead, it is hypothesized to be a gigantic, thick, spherical bubble made of icy space debris completely surrounding our solar system.
While the planets orbit in a relatively flat plane, comets visiting our inner solar system can streak in from completely random angles—top, bottom, and sideways. In the 1950s, Dutch astronomer Jan Oort proposed that these comets must be falling inward from a gigantic, 3D sphere of icy debris completely enclosing the solar system.
The Home of Comets
The objects in the Oort Cloud are incredibly ancient, composed of water ice, ammonia, and methane leftovers from the very formation of the solar system 4.6 billion years ago.
Occasionally, a passing star or gravitational tide from the Milky Way will disturb one of these icy chunks. The chunk gets nudged out of the cloud and begins a long, millions-of-years freefall toward the Sun. As it gets close to the Sun, the ice boils and leaves a stunning glowing tail. We call this a Comet.
How Far Away is it?
The scale of the Oort Cloud is terrifying. It is located roughly 2,000 to 100,000 Astronomical Units (AU) away from the Sun. (One AU is the distance from the Earth to the Sun!).
To put that in perspective, NASA's Voyager 1 spacecraft has been flying at 38,000 mph since 1977. It has passed all the planets and entered interstellar space, yet it will still take Voyager about 300 more years just to reach the inner edge of the Oort Cloud, and nearly 30,000 years to fly through to the other side!
