[X] My Assistant

[SFJCody]

http://groups.yahoo.com/group/mpml/message/15111

[Guest_BruceMoomaw_*]

Alan Stern: "The one comment I'll make here is that we have been
careful not to insist that an object BE spherical, only that it be massive enough
to become spherical. This avoids issues like the one you brought up (who
spherical does it have to be?), as well as issues related to rotational
flattening (ala Jupiter and Earth)."

Ah, but whether an object is "massive enough to become spherical" depends on what kind of substance it's made of, and thus how rigid it is. And determining that is a lot more difficult than determining how spherical it actually is.

Moreover, we once again have the problem of fuzzy borders. Pallas (which Mongo accidentally left off his list of Class 3 planets) and Vesta are mildly but significantly non-spherical, and NOT because of rotational flattening. Among the moons, so are Iapetus and Mimas -- to say nothing of Neptune's second-biggest moon Proteus, which looks like nothing so much as a giant marshmallow. And given the number of KBOs, there are bound to be a lot of them that fall into this "Is it spherical or not?" category.

Parenthetically, has anyone come up with a convincing explanation for why Pallas -- alone of all significantly large asteroids -- has that incredible 30-degree orbital tilt? Either something really big ran into it (in which case one would tend to think its parent body would have shattered into multiple objects), or something even bigger brushed past it and tidally yanked it into that orbit.

[abalone]

Alan Stern: "The one comment I'll make here is that we have been
careful not to insist that an object BE spherical, only that it be massive enough
to become spherical. This avoids issues like the one you brought up (who
spherical does it have to be?), as well as issues related to rotational
flattening (ala Jupiter and Earth)."

The chondrules that make up carbonaceous chondrites what about them?

"A roughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at about 1400°C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5 to 2 mm in diameter and are usually composed of iron, aluminum, or magnesium silicates in the form of the minerals olivine and pyroxene, with smaller amounts of glass and iron-nickel. Together with calcium aluminium inclusions, which predate them by a couple of million years, they are among the oldest objects in the Solar System with an age of about 4.57 billion years. They formed when dusty regions of the solar nebula were heated to very high temperatures, became molten, and then resolidified as tiny droplets. "
From http://www.daviddarling.info/index.html

Were they all once planets and are there enough combinations of letters to name them all if they were?

This shows the pointlessness of trying to invent rules where none are needed.

[Alan Stern]

Chonrules are spherical due to surface tension, not gravity. It's not that
an object *is* spherical, the thing that counts, that reveals it acts like a planet in
a fundamental way, is that it is massive enough to have its shape controlled
by self-gravity.

[abalone]

Chonrules are spherical due to surface tension, not gravity.

I realise this Alan, I was just taking the rule to its ultimate extreme. Exactly how big would it have to be before gravity is stronger than surface tension, 10m, 50m certainly by 100m?
If there was a material that had no surface tension then gravity would cicularise it irrespective of mass and if a 100km lump of rock had enough internal heat generated by short lived radionucleides it would melt and form a sphere due to gravitational forces in the brief time before it resolidified, but now I am getting ridiculous again

It is like making up a rule for what constitutes a tall or a rich person

[dvandorn]

I've been enjoying the discussion, actually. It's obvious that human beings need to classify things into systems -- it's how we look at things. And whenever you get into defining rules for systems, you get into such wonderful discussions as this...

Alan, believe me when I say that I respect your opinion and your accomplishments. Quite a bit. I've also enjoyed how you have stuck to a single set of referents within the argument, no matter how many people have tried to place their own rules onto the system.

I still think there need to be more useful and handle-able subclassifications within the system for "popular consumption." But other than that, your logic holds sway, Alan.

-the other Doug

[abalone]

  It's obvious that human beings need to classify things into systems
-the other Doug

Classification is a good and noble scientific cause but the group of bodies orbiting our sun that we call planets dont have a lot in common. Any classification system that puts Jupiter in the same group as say Mars or Mercury is not really of any scientific relevance and more for lay media consumption. It would be difficult to convince me that Mars has more in common with Jupiter than it has with Pluto.