Let's please have a general thread about the Solar system.
I grew up with the nine-planet model, and therefore watched with extreme pleasure as New Horizons photographed Pluto-I'd been wanting to see pictures of it since I was a kid. I also tuned out the multiplicity of new bodies/KBOs for some years, being busy with life. However, I've re-visited the subject, and to self-teach, I followed along with wiki to build an arbitrary version of the largest known bodies in the solar system at the moment, and (sometimes) their attendant satellites.
I've scared people off with my autism enough times in OPs to know not to lay it on too thick in the OP itself. But in later posts, I'm going to get autistic. I have substantive questions.
Charon and Pluto are a double dwarf planet with 4 moons.
Why is everyone always so concerned with pluto. There are far more interesting worlds in the system to obsess over, not to mention probably a dozen more KBOs bigger than pluto still floating out there. Fuck pluto.
Dwarf planets are still planets, but as a sub classification.
Its a requirement as our understanding of the solar system grows and simply calling everything big orbiting the sun a planet is too vague.
A comparison of the solar system's largest known bodies (and the satellites pertinent to those bodies) led me to produce this draft image of current understanding.
Basically, the landscape as I see it is: a star, the planets, their satellites, and finally the dwarf planets and their satellites. (then other detritus, being rings, asteroids, whatever's going on in the Oort cloud, etc). I wanted to push my understanding just out to the KBOs/TNOs just a bit, which is why I made the thread.
Things I learned for the first time, during my babby reading:
-Mike Brown and Alan Stern are Big Guys in planetary science, at the vanguard of their field. That's gotta be comfy.
-I infer that Hydrostatic equilibrium is just a very fancy phrase for "a medium settles down into a sphere". But why are basically-spherical bodies sometimes not regared as "in HE"? Something about density of material I bet.
-Mass is the thing that they can measure with the most confidence, without need of tolerance intervals. And yet, very distant objects which do not have their own moons are not amenable to meaningful mass estimates/measurements. This is surprising to me, I wonder if anyone can help me out.
Because most people didn't comprehend the solar system beyond the sun, the (then) 9 planets and the asteroid belt. Hell even now most people don't know what the Kuiper belt is.
It doesn't help that the IAU decision process was hamfisted, the current definition needs work and there are a bunch of bodies that are clearly dwarf planets but have not been officially deemed so.
I did explain myself somewhat in the OP (and I've done this in the past during the initial New Horizons success), but let me do it again to deaf ears.
Just to my right, I have a book by Bill Yenne, "The Solar System", published 1990. Its source material includes the wonderful Voyager 2 photography, and it also includes some Venera images, so I knew what the Soviets had accomplished. Dad got it for me when I was a little kid, whoa, planets dude. Then pluto... (artists' conception).
That stupid bogus artist's conception stuck in my craw for over two decades, finally getting release in the first half of 2015. I love, love, LOVE that my tax dollars were involved in this <3.
The point being that a Pluto mission eventually became feasible, and represented a personal delayed gratification, pertinent to history. The other objects are academic right now.
Unrelatedly, I'm told there is a planetary lineup in the early morning sky, for the next few days! But I think it's going to stay overcast here...
>But why are basically-spherical bodies sometimes not regared as "in HE"?
Example of a basically-spherical body you think should be counted as in HE?
Note that HE does not equate a sphere, as they are typically fatter at the equator due to spin.
>a rose by any other name would smell as sweet
Whatever you decide to call something doesn't change the fact of what it physically is. Pluto remains unchanged despite what the astronomers want to classify it as.
The IAU definition is lame and we all know it.
I'm not arguing that xyz should be "counted as in hydrostatic equilibrium". I understand now that there's plenty in contention where planetary science is concerned, to the point that "culturally" it would be easy to suppose I'm arguing something. But that's not the case.
Rather, I'm simply stating that /I don't have a detailed understanding of what hydrostatic equilibrium is/, beyond the gravity-pressure-sphere thing in wiki's treatment.
So when I see an Iapetus or a Mimas, I'm not telling other scientists their business just because "durr it's round". I just want to understand how they're presently drawing that distinction (as they are):
What is contentious about it?
>An object in hydrostatic equilibrium is one that is large enough for its gravity to have overcome its internal rigidity, and so relax into a rounded (ellipsoidal) shape.
>Ceres, Pallas, Juno and Vesta are all planets
Despite that article's pat summary (wiki has a mission to always simplify), multiple things.
1) if you read a bit further in the article you linked, you never find unequivocal language in the poorly worded later segment that "yes, the moon etc are in HE".
Now, it is true that wiki is a secondhand source, often prepared by others in an effort to improve their own personal understanding. But even elsewhere in my link, it is established that such-and-such are NOT IN HE (Mimas, say).
The larger point being that for whatever reason, "Hydrostatic equilibrium" and "rounded by its own gravity" seem not to be coterminous concepts (per wiki), though closely related ones. And this, I suspect, because of the healthy autism fight currently taking place in planetary science, which just shows us that this is a vital area of the sciences where something interesting is going on.