This is a list of astronomical objects with the spectral type Y. They are a mix of brown dwarfs and planetary-mass objects.
Spectral type Y objects are not all brown dwarfs, they just have a similar elemental composition. Jupiter doesn’t have the mass to be considered a brown dwarf, they are 13-80 times the mass of Jupiter by definition.
That mass-based definition is outdated and does not consider recent observations of the interiors of Jupiter and Saturn made by the Juno and Cassini spacecraft. It is a reflection of cold-war era fusion chauvinism and is due to get an update. Jupiter is a star, Saturn straddles the boundary between star and planet.
Jupiter is a star, Saturn straddles the boundary between star and planet
I would suggest that a brown dwarf straddles the line between star and planet (the Wikipedia page begins with (“Brown dwarfs are substellar objects”) and that therefore Jupiter is, at best, straddling the line between star and planet, and therefore Saturn is solidly a planet.
I believe there is an object called a brown sub-dwarf which jupiter would clasify IF it wasn’t part of a planetary system that basically represents the smallest type of failed star, however since jupiter formed from a protoplanetary disc it is indeed a planet. It really is a bit of an issue with our classifications that they’re context dependant though. E.g the moon on its own could be a dward planet, earth orbiting at the same distance as pluto would also be a dwarf planet even with no other changes.
I like what you’re trying to do, but I disagree with merging brown dwarfs with planetary class objects because their interior structures and evolution are so different. Brown dwarfs are closer to stars than planets. The only difference between brown dwarfs and fusing stars is whether fusion occurs at the core. Planets are very very different in structure, morphology, and evolution.
This is how I suggest we classify things:
Let’s start by splitting things into two classes: planetary class and stellar class with Saturn at the boundary. This is a separation based on internal morphology and dynamics.
Stellar class objects then get split into two further subclasses: fusing stars (suns) and non-fusing stars (brown dwarfs).
Saturn exists at the boundary between the planetary class and the stellar class. Jupiter is solidly within the “brown dwarf” non-fusing stellar class of objects. The sun is a “fusing star”, which is also within the stellar class.
