No Iceball Left Behind

[catbirdseat]

Twelve Planets?

 

The new ones: Ceres, Charon and Xena. Ceres is an asteroid, Charon is Pluto's "moon", but more of a twin, Xena is a distant ice ball, larger than Pluto, and part of the Kuiper Belt.

 

The definition of a planet? It must be round and not a moon. Charon doesn't count because the center of gravity of the pair is between them and not inside Pluto.

 

I think they ought to just cut it off at 8 planets, excluding Pluto.

[lI1|1!]

[Dechristo]

I think they ought to just cut it off at 8 planets, excluding Pluto.

 

God heard your petition. She is now removing the offending iceballs.

 

 

[archenemy]

I'll be Pluto tastes bitter.

[Dechristo]

[archenemy]

Better proportions and tastier

[Dechristo]

Feet held to the fire for semi-flacidity.

[Fairweather]

http://news.bbc.co.uk/2/hi/science/nature/4795755.stm

 

If UB313 is larger than Pluto/Charon it certainly deserves inclusion in the 'planet' family. But honestly, I wasn't aware that the asteroid Ceres was a sphere. Doesn't the fact that a planet or moon is near-sperical indicate it has - or had - a molten core? Anyway; this debate all seems like semantics to me. Prematurley categorizing every conceivable object we encounter in the universe down the road will probably just narrow our collective view.

[olyclimber]

WTF is it with "Planet's Rights" these days? What rights do they have? Can't we just take away their planethood, and kick their ass out into the street?

[Dechristo]

I, for one, wouldn't have bought land on Pluto had I known it's planethood was in jeopardy.

[Cobra_Commander]

uranus

[catbirdseat]

http://news.bbc.co.uk/2/hi/science/nature/4795755.stm

 

If UB313 is larger than Pluto/Charon it certainly deserves inclusion in the 'planet' family. But honestly, I wasn't aware that the asteroid Ceres was a sphere. Doesn't the fact that a planet or moon is near-sperical indicate it has - or had - a molten core? Anyway; this debate all seems like semantics to me. Prematurley categorizing every conceivable object we encounter in the universe down the road will probably just narrow our collective view.

A planet would not need ever to have been molten for it to form into a sphere. The only requirement is that is mass and hence gravity be sufficient for it to collapse into a sphere.

 

It is said that if Mt. Everest were much larger it would collapse under it's own weight. Perhaps one reason why Olympus Mons on Mars is so tall is the lower gravity. I would hazard to that if one were to measure the angle of repose for that mountain, it wouldn't be all that steep. It has a huge base.

[Dechristo]

is that the one with rings around it?

[Cobra_Commander]

its the one with acres of cheap real estate around it (etc, etc)

[Dechristo]

Is its plant-it-hood in question?

[olyclimber]

It the one with the big moon.

[Fairweather]

A planet would not need ever to have been molten for it to form into a sphere. The only requirement is that is mass and hence gravity be sufficient for it to collapse into a sphere.

 

 

Obviously not applicable to the 4 gas-giants, but can a rocky-bodied planet really collapse/spin itself into a sphere at less than some minimum mass? At some critical mass/density of material the core of a sperical body would have to become hot/molten - wouldn't it? I suspect the gravitational forces of an orbiting body (moon) would lower the threshold even farther. I'm sure there is a mass/density/gravity formula, but I'm too lazy to investigate right now.

[foraker]

The ability of a planetismal/planetary sized body to become molten would depend on the mass infall rate (energy to melt things, depends on attractor size on availability of impactors) versus the rate that energy could radiate away from it's surface (cooling). If the infall rate were 'too small', a planetismal would not have to be 'spherical' per se, just lumpy. Fortunately, in the early solar system, infall rates were high and proto-planets were likely surrounded by an insulating gas/particle cloud. This would have helped the silicate planets to be initially molten (even without it, they probably would have melted simply because of the high infall rates) . The icy planets would have no need to be actually melted, I think, as two effects would help to 'melt the ice'. First, you have impactor energy. That should simply melt things upon impact which would then seek an equilibrium with the geoid. Second, as the planet grows, the internal temperature of the planet will rise due to the effects of compressibility. I'm not sure, but this is probably too weak to initiate anything but very slow overturning in the ice mantle. For things like the Jovian moons, you also have things like tidal forces from the main planet providing energy to melt things.

[Dechristo]

Then why are Planet Hollywood's square?

[G-spotter]

[

 

It is said that if Mt. Everest were much larger it would collapse under it's own weight.

 

I can tell you're a chemist and not a physicist

[catbirdseat]

[

 

It is said that if Mt. Everest were much larger it would collapse under it's own weight.

I can tell you're a chemist and not a physicist

I read that somewhere in a newspaper article. You don't have to believe it. The process of weathering is what generally limits the size of mountain peaks.

[G-spotter]

I can tell you aren't a geologist either, now, too!

[foraker]

This from the man who buys the deep biogenic origin of oil...

[cj001f]

he's not a geologist either, he just plays one on the interweb

[Dechristo]

Well, aren't we all just geolly this morning.