Today, the International Astronomical Union places the dividing line between brown dwarfs and planets at 13 Jupiter masses. This is the minimum mass required to ignite deuterium fusion.
IAU is well known for coming up with shitty arbitrary classifications about nomenclature that many astronomers don’t agree with. They are wrong here because they don’t take into account post-Cassini/Juno understanding of gas giant morphology. The IAU definition is outdated and highly misleading.
Copied from another reply I gave in this thread:
I’ve seen 13 MJ argued as a boundary, but it’s selected somewhat arbitrarily and based around idealized models of Deuterium fusion, which has never been observed, and which is a process these brown dwarves would only undergo for a brief flash in their early life. Deuterium isn’t abundant enough for its fusion to significantly alter the stellar morphology that has already become established for objects larger than Saturn. Saturn is our solarsystem’s example of an object that does not fit cleanly into one side or the other of a mass-based binary classification scheme for determining a hard boundary between “planet” and “star”. To understand what is a planet vs what is a star, study Saturn.
The planet definition that excluded pluto was decided upon at the end of an IAU conference after most planetary scientists had left. As a result, only dynamicists are happy with it. Planetary geologists in particular HATE it and have always vocally pushed back.
As someone who worked as an astrophysicist for 9 years, I assure you that the question of “what is a planet?” is a nuanced discussion with a lot of diverse opinions and no clear answer that gets endlessly debated by students as they learn that these definitions aren’t as cut and dry as irresponsible science communicators made it seem during the disastrous and highly politically motivated demotion of Pluto to dwarf planet.
Jupiter is large enough for the hydrogen to become a plasma and dissolve the rocky “planetary” core that was once at the center. Morphologically, it has passed the transition from planet to star. Saturn appears to be somewhere along that transition and is harder to cleanly classify.
Morphologically, Jupiter is a star.
I’ve seen 13 MJ argued as a boundary, but it’s selected somewhat arbitrarily and based around idealized models of Deuterium fusion, which has never been observed, and which is a process these brown dwarves would only undergo for a brief flash in their early life. Deuterium isn’t abundant enough for its fusion to significantly alter the stellar morphology that has already become established for objects larger than Saturn. Saturn is our solarsystem’s example of an object that does not fit cleanly into one side or the other of a mass-based binary classification scheme for determining a hard boundary between “planet” and “star”. To understand what is a planet vs what is a star, study Saturn.
It’s a Y-class brown dwarf star. Saturn likely is as well.
Apparently not though:
IAU is well known for coming up with shitty arbitrary classifications about nomenclature that many astronomers don’t agree with. They are wrong here because they don’t take into account post-Cassini/Juno understanding of gas giant morphology. The IAU definition is outdated and highly misleading.
Copied from another reply I gave in this thread:
Ok, that’s interesting! I didn’t realize there was controversy around this definition.
The planet definition that excluded pluto was decided upon at the end of an IAU conference after most planetary scientists had left. As a result, only dynamicists are happy with it. Planetary geologists in particular HATE it and have always vocally pushed back.
And if you want more, check out what I said last time this meme was posted.
As someone who worked as an astrophysicist for 9 years, I assure you that the question of “what is a planet?” is a nuanced discussion with a lot of diverse opinions and no clear answer that gets endlessly debated by students as they learn that these definitions aren’t as cut and dry as irresponsible science communicators made it seem during the disastrous and highly politically motivated demotion of Pluto to dwarf planet.
I’d say Jupiter would need to be about 3 times massive to count as one. And more realistically around 10ish.
Based on what criteria?
Jupiter is large enough for the hydrogen to become a plasma and dissolve the rocky “planetary” core that was once at the center. Morphologically, it has passed the transition from planet to star. Saturn appears to be somewhere along that transition and is harder to cleanly classify.
Morphologically, Jupiter is a star.
I’ve seen 13 MJ argued as a boundary, but it’s selected somewhat arbitrarily and based around idealized models of Deuterium fusion, which has never been observed, and which is a process these brown dwarves would only undergo for a brief flash in their early life. Deuterium isn’t abundant enough for its fusion to significantly alter the stellar morphology that has already become established for objects larger than Saturn. Saturn is our solarsystem’s example of an object that does not fit cleanly into one side or the other of a mass-based binary classification scheme for determining a hard boundary between “planet” and “star”. To understand what is a planet vs what is a star, study Saturn.