Although the Kuiper Belt and the Oort Cloud were both proposed long ago, the first large objects (e.g., Quaoar, Varuna, and Sedna) that are in these regions of the Solar System were only discovered recently.
a. What are the properties that prevent these objects from being easily observed?
b. Why is it considered likely that there may be other Pluto-sized objects in these two regions that have not yet been discovered?