If you have any interest in astronomy, you have probably heard of the Oort cloud. It is considered to be a large sphere of comet-like bodies orbiting the Sun and is claimed to be the source of long-period comets. The major problem with all the hype surrounding the Oort cloud is the fact that there is no actual evidence that it even exists.
The only reason why the Oort cloud is thought to exist is because of the fact that we still have long-period and short-period comets. This fact, particularly the short-period comets, is inconsistent with a solar system that is 4.5 billion years old. This was simply a solution proposed to deal with a piece of evidence that naturally points to a young solar system by placing an unobservable reservoir of comets at great distances from the sun.
When you look at how big and far from the sun the Oort cloud is supposed to be, it is clearly designed to make the claim pretty much untestable. The innermost part of the ort cloud is supposed to be about 90 times further away, than the distance of the farthest dwarf planet (Sedna) that has been discovered. Based on the size of comets, their low temperatures, and the dimness of the sun at such distances, these objects would not be observable even if they existed.
The simple fact of the matter is that there is no actual evidence that the Ort cloud even exists. The only reason for even concluding that it exists is that it is necessary to make a 4.5-billion-year solar system work. These are not the only problems with these models, they keep inventing untestable ways to explain away the problems. Consequently, the biggest secret of the Ort cloud may be that it doesn't even exist.
