The Oort Cloud

The Oort cloud is an outer shell of frozen particles at the border of our solar system, so far away that we lack the technology to even detect it. Our last chance to image the Sun is with Voyager 2, which would take another 300 years to get there since the Sun is too far away for its light to reach us. That raises the issue of how we even know it exists.

It all began with a Dutch astronomer named Jan Hendrik Oort who was attempting to comprehend long-period comets in the 1950s. Long-period comets take thousands of years to complete an orbit, unlike short-period comets, which usually return in a few hundred years. They also appear to come from random places in the sky rather than following the regular orbits of short-period comets.

His response, the Oort cloud, is now generally acknowledged as the cause of long-period comets. We only really know that it is a large region of the Solar System's frontier made up of frozen bodies of diverse sizes and shapes. Even though the Oort cloud is unquestionably the largest structure we are aware of in the Solar System, we have no idea how it was created, how thick it is, or what material its bodies are made of.