What is beyond Pluto?
There are many, many objects beyond Pluto, but where they came from and when they formed is a whole other question.
A notion came along that Pluto did not form in the solar system, but that it was captured and came from further reaches of space. Eventually after much debate, the International Astronomical Union accepted Pluto as a planet, but a dwarf planet.
There are many other objects like that, some bigger than Pluto, and some twice as far away as Pluto is. We don’t know the number because they don’t emit their own light. They’re so far away, it’s not easy to detect them.
We see planets only because they are reflecting light from the sun. There are many stars similar to our sun, and those stars can also have planets. We now know that there are at least 4,000 objects that are like planets going around other stars.
Reflected light comes in a variety of colors. The human eye can see the rainbow spectrum, visible light, but there are other things we cannot see including ultraviolet light and infrared.
Space is full of a lot of stuff, including dust. Shorter wavelengths cannot penetrate through a lot of dust, but the longer wavelengths can. Using infrared allows scientists to see objects further away, so many new discoveries come from using powerful telescopes and looking at the longer wavelengths.