What is #32: The Oort Cloud?

I recently took a look at the Kuiper belt in this 'What Is' series, making mention of the Oort Cloud. The Kuiper Belt is a region of icy objects, including many comets that exists near the orbit of Neptune between 30-50 AU from the Sun. But what is the Oort cloud?

The Oort cloud is another region of icy objects in the Solar System, but extending to much greater distances. The Oort cloud starts at a few thousand AU from the Sun and extends to distances greater than 100,000 AU. There are potentially billions of icy objects in this vast region of space.

Long period comets, with orbits taking several tens of thousands to hundreds of thousands years, come from this region in space. We can't see anything that exists out in this region given they reflect so little sunlight back to us. Models of solar system formation shows icy bodies were likely thrown outward to the outer solar system by the formation of large planets in the inner solar system. We see objects from this region when they fall inward as comets and flare up as they come close to the Sun. A mapping of the orbit tells us these comets came from the Oort cloud.

Consider the Oort cloud a graveyard of icy objects that are floating around in the outer solar system waiting their turn to make a trek toward the Sun. A bit lonely, but it's astronomy, so still very exciting!