IAU Announces Tomorrow Morning
So, let's call it eight planets, okay?
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
And some other smaller stuff like asteroids, planetoids, centaurs, trans-Neptunian objects, Kuiper-belt objects, and other names that overlap. You can call these minor planets or dwarf planets or whatever you like. That's where these go:
Vesta
Ceres
Pallas
Hygiea
Pluto
Orcus
Ixion
Varuna
TX300
"Santa"
Quaoar
"Easterbunny"
AW197
"Xena"
Sedna
And anything that orbits one of the above categories, we'll call a moon or a satellite. Unless it's like really really close in size. And we haven't found any of those yet. Thus go:
Moon
Io
Europa
Ganymede
Callisto
Titan
Triton
Charon
"Gabrielle"
Back to the status quo, in other words. Except Pluto has finally been reunited with its heretofore unknown compatriots.
7 comments:
To the second list, add "and untold numbers of asteroids generally between the orbits of Jupiter and Mars, the comets, and a smattering of Trojan objects 60 degrees ahead and behind the larger planets."
To the third list, add "and untold numbers of smaller satellites, rings, and other debris circling the planets."
I have a suggestion for distinguishing between planet-moon and double-planet: if the center of mass for the pair is inside the larger object, then it is a planet-moon. That should be easy to calculate. Hmm, I wonder how earth-moon rates?
The IAU has debated that definition of a double planet. We'll see if they adopt it. Earth-Moon would not qualify, but Pluto-Charon would.
In hindsight, I was wrong to include asteroids in the category for dwarf planets in my previous post. There should be a distinction between dwarf planets and rocks (asteroids, comets, debris orbiting the sun). I should have suggested that a dwarf planet has to have enough self-gravity to pull itself into a round shape.
So, with that, how many dwarf planets have been identified? I think Santa will then be the largest rock, and there will be dwarf planets that are smaller than Santa but round.
Except that Santa isn't a rock. It's a snowball. Not to be confused with Snowball II or Santa's Little Helper.
Actually, I believe that 2003 EL61 (Santa), would still count as a dwarf planet becuase the definition uses the term 'hydrostatic equilibrium (nearly round) shape', and that can include objects which are distorted due to rapid rotation or tidal forces (like Saturn).
If Soto's description and gravitational analysis of Santa is correct (in his previous post), it is definitely not in hydrostatic equilibrium. He described it as seeming to be two mountains with very different gravitational pulls in the "valley" and on the "mountain" top. He is describing something more cigar-shaped, not a squashed ball like Saturn. Hydrostatic equilibrium would imply that the pull of gravity would be almost constant everywhere, maybe slightly less on the equator.
Well, Santa's dimensions are apparently 2000 km x 1500 km x 1000 km, roughly. So something is keeping it from being a pure discus like Saturn. And it's spinning so fast that the poles are incredibly closer to the center than the equator is.
I'm willing to call it a dwarf planet. Let's see what the IAU decides (next year? the year after?).
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