It astounds me, awes me, and fuels my imagination to no end. A very long time ago, in a dream, I sat on Pluto. It was all but dark, and it was covered in rocks and a thick layer of dust. I knew it was cold, but I didn’t feel it. And what I saw as I sat on a rock on Pluto was a (then) tenth planet.
It was much larger than Jupiter, and it seemed to be lit up from the inside.
I much later came to hear about PlanetX, which still fits because X in Roman numerals is 10! :)