Astronomers at Caltech and elsewhere have estimated the mass of planet 9 to be in the range of 9-12 earth masses
https://www.caltech.edu/news/caltech...h-planet-49523. Brown Dwarf stars are discussed in terms of Jupiter Masses, which is 317.83 earth masses
https://en.wikipedia.org/wiki/Jupiter_mass. The expected range of a brown dwarf star is 13-75 Jupiter Masses; in short, there is no evidence for a brown dwarf or failed star existing in our solar system.
I think it's fascinating that there could be a large, undiscovered planet out there. But let's not get carried away in our excitement. Perhaps read a little more and youtube less!
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