[Foskya]

I guess it is more of a derivative of the question: "in which bucket should we put the brown dwarf? Is it a star or a planet?". The answer is neither of course; but since it is more closely related to stars than to planets, I'm more inclined to call this satellite an exoplanet (instead of exomoon).

That being said it is still a nice finding, way more difficult to discover than "normal" exopanets.

[selectodude]

I thought we’re supposed to call them dwarf planets now. Dwarf star, dwarf planet.

[GolfPopper]

It's a problem of useful/meaningful labeling.

'Planet' comes from the Greek word for 'wanderer' which was very useful for labeling the handful of bright stars that moved through the heavens in a pattern. Then we got to the Space Age and kept calling them (and similar new additions) 'planets' even as we learned far more about them. And immediately there's a problem. Setting aside Pluto (and the Sun), you've still got Mercury on one end (5% of Earth's mass, and smaller than several moons) and Jupiter on the other end (320% of Earth's mass - more than everything else in the solar system put together, and over 1000 times Earth's volume). "Planet" stops being a word you can use with any sort of detail. (Thus the IAU definition battle and Pluto's "demotion".) Astronomers have pretty good terminology for stars, but once you go sub-stellar, the labeling rapidly gets difficult, and for good reason.

[NooneAtAll3]

> and Jupiter on the other end (320% of Earth's mass

not %

just 320 Earth masses

[Aerolfos]

> Astronomers have pretty good terminology for stars,

...do they though?

The "proper" terminology says all main sequence stars are dwarves, but nobody calls them all that in practice. Some astronomers insist on saying "yellow dwarf", but some don't really bother. In general having the only two kinds of star be "giant" or "dwarf" is contentious, but it's also contentious that there isn't a name for whatever is in the "middle". "Main-sequence star" is a broader category and doesn't apply. They're all "stars", obviously, so that isn't specific enough.

The only decent terminology is for the spectral classes, but those only work as long as you look at spectra. The moment you try to figure out what the theory says those stars would look like as proper 3D objects, things get very messy. You also immediately get the issue that star size and brightness goes O>B>A>F>G>K>M. So... it's alphabetic except it isn't. And C is something completely different and doesn't fit the brightness classification at all.

[delta_p_delta_x]

Even within stars the layman labels are a bit iffy; it is better to use the stellar classification. 'Dwarf' is badly overused, as is 'giant'.

[askvictor]

Small-statured-person planets.

[rbanffy]

Diameter-challenged star

[ludicrousdispla]

Anybody know why the brown dwarf isn't considered a planet?

[gnabgib]

Because a brown dwarf is a star? https://en.wikipedia.org/wiki/Brown_dwarf

[ludicrousdispla]

Where is the rule that says a star can't also be a planet?

[rbanffy]

As far as I'm concerned, CD-35 2722 B can self identify however they want.

If they want to identify as a planet, however, they can claim the almost unique distinction of having a gas giant as their moon. I wonder if the gas giant itself has their own small rocky and potentially habitable moons.

[foolfoolz]

Planet++