Astronomers discover new dwarf planet 'Ammonite'

[Lorizael]

#3

[Buster's Uncle]

Popular fellow, even there.

[Geo]

Every culture in history, for thousands of years, recognized that there were only 5 planets, until a British colonizer spotted a big weird ice ball out there and named it after his king.

Herschel is not an English name... 

[Lorizael]

Neither is Hanover or Saxe-Coburg, but what can you do.

[Buster's Uncle]

Bow to our Germanic masters...

[Lord Avalon]

If Pluto is a planet, then surely you would include Eris. While smaller in diameter, it is more massive than Pluto.

[Buster's Uncle]

One is an old friend -maybe family- the other is a stranger I do not know to love.

I'm comfortable on this hill.

[Lord Avalon]

That ain't science.

[Buster's Uncle]

I guess maybe not, but I'm still comfortable on this hill.  Pluto should have been grandfathered in, not that bothering to finally define what a planet IS was otherwise a bad thing.  The lack of a definition was sloppy and unscientific.

[Lorizael]

I'm... just going to paste bits of something I wrote years ago when Alan Stern (PI of the New Horizons mission) got an OpEd in the Post about how his ball should be a planet.

Historically, for thousands of years, planets were defined entirely by their orbital characteristics and not even a little bit by their physical properties. If we still want to use the word planet today in a scientific sense, we can either (a) hew to their historical (orbital) origins, or (b) divorce ourselves from that notion and ground our definition in something a little more rigorously physical and scientific.

If we want a scientific notion of planet, what we're looking for is a term that is explanatorily useful. In the protoplanetary disk, are different physical processes responsible for creating different hunks of matter (accretion versus collapse)? In mature solar systems, do we see geographically distinct regions (main best asteroids versus trojans)? If there are such rough divisions, then distinct taxonomic categories become useful. We can say that zirbadube-type objects formed via mejazolistic-like processes and ended up in the squanomok region. Without taxonomies, we're required to be reductive. Then a question like "how did the solar system form?" can only be answered with "physics."

Of course, this sounds eminently reasonable, and people like Stern and Grinspoon would probably say that's what they're doing. And maybe they are. But the claim that it's obviously correct for historical, common sense, and scientific reasons that Pluto is a planet and that others are necessarily being dictatorial or unscientific is... well... hyperbolic. The solar system is a much bigger and weirder place than we imagined it to be even a few decades ago. We should have lively discussions about how it all fits together. But there's no reason to frame this as a battle over the rank and status of one very cool ball of ice and rock in the Kuiper belt.

For planetary scientists, I think planet is probably too general a term to be all that useful. Terrestrial planets, gas giants, and ice giants all seem very different except for being spherical non-stars. In the Planetary Data System, there are separate nodes for atmospheres, geosciences, cartography and imaging sciences, planetary plasma interactions, ring-moon systems, and small bodies. Titan, which the authors call out as being a "planet moon," has datasets in almost all of these nodes depending on mission parameters. To my mind, planetary scientists don't need a definition. They all know they're studying big rocky icy gassy things in the solar system. They're much more likely to have a fight about the technical differences between, like, meteorite subtypes.

For astronomy more broadly, however, I think the historical conception has value. Planets are wanderers--the objects that stick out from the surrounding stars. They're the features by which we characterize a solar system. Oh, that system has 3 hot Jupiters. That one has an Earth twin. From that standpoint, we only care about the big, round bodies that play a role in the dynamics of the system. Something like Pluto is one of our many kuiper belt objects--cool and worth studying--but not one of the defining features of the solar system.

[Buster's Uncle]

The defining feature of our solar system is the star, well north of 99% of it.  The rest is niggling detail.

[Lorizael]

And yet the rest of the planets are gravitationally significant if you want to understand the structure and evolution of the solar system.

[Buster's Uncle]

Those leftover specks?

Give me back Pluto, and you can have your dirt.


Note:  I'm actually semi-serious.

[Geo]

Those leftover specks?

Give me back Pluto, and you can have your dirt.


Note:  I'm actually semi-serious.

You still have Pluto. It just has a nomer in front of it, like Earth is a "rocky" planet, Jupiter a "gas" planet, so is Pluto (and Ceres, and Eris,...) a "dwarf" planet.

[Buster's Uncle]

It's like Star Trek, only backwards.