[X] My Assistant

[SFJCody]

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

[abalone]

What peculiar little creatures we humans are that we find it necessary to have everything assigned to its correct pigeon hole. I cant see the slightest relevance to this decision as to whether we call it a planet or not. " It orbits, therefore it is" and "A rose by any other name would smell as sweet"

[dilo]

Based on the ongoing discussion, I made following flow diagram in order to adress main objection rised up to now.
 PIANETI.DOC ( 19K ) Number of downloads: 504

This general method should correctly discriminate between a natural satellite (a planet if central body is a star or a moon for an object orbiting a planet) and a planetoid/”satelloid” isolated or belonging to a wide population like asteroids belt or KB.
Obviously, this is only a sketch and numerical constraint on radius and semi-major orbit can be revised... Anyway, I deribely avoided to use absolute measures (like size in Km) in order to have a general method that can apply also to planet/moons systems. Obviously, these pure numbers are choosen in order to include all solar system planets; inclusion of Pluto and other major KBO could be temporary, because it depends on future discovery of other objects with similar orbit. This is the normal historical process higlighted by Alan...

[Alan Stern]

Dilo--I wonder, what will you do when Mars-sized and larger objects are found in the
Oort Cloud on highly elliptccal orbits that range over the same distance from the Sun?
Classify ejected Mars- and Earth-sized bodies as planetoids? And what about in
extra-solar planetary systems in formation where one routinely expects very large
bodies (Mercury to Uranus sizes) on crossing orbits? Can only the single largest
one be a planet? If an object is small compared to its neighbors but ejected to
a place where it is large compared to its new neighbors, does it get promoted
to planethood just by virtue of lits change in location? If the reverse happens,
do you propose the object be demoted, as the flowchart algorithm suggests
one would have to do?

Localtion and relative-size arguments always have these problems. Planets are planets
because of what kind of body they are. I remain convinced it is better to pick a good
criteria-- like being rounded by gravity-- and let the number of bodies be whatever
Nature delivered.

-Alan

[MiniTES]

Localtion and relative-size arguments always have these problems. Planets are planets
because of what kind of body they are. I remain convinced it is better to pick a good
criteria-- like being rounded by gravity-- and let the number of bodies be whatever
Nature delivered.

Alan: What about Ceres and Vesta? Do you think that we should call them planets by virtue of their shape? Personally I agree with your scheme but I don't think it would be logical to call Ceres and Vesta planets instead of asteroids.

[Alan Stern]

I do think Ceres is a planet: a dwarf one, but no less a planet than a 100 Mj object
is a star.

I wrestled with this whole question a long time ago, and I think the fundamental
difference between a planet a a big rock is that a planet does something collectively--
i./e., it shapes itself into a sphere by graivty overcoming maerial strength. Anything
too small to do this is acting like a rock. Anything beig enough to do this, but
not so big that it does fusion, is a planet.

And as I point out in public talks sometimes, though many, amny adults claiim
to have never thought about this, any kid knows it: jst ask a kid to draw
a planet; they always draw a circle, never an egg or a box or a pyramid or
even a hamburger. Kids know planets are things that are essentially spherical;
of course most don't know why this is so, but they recognize the observational
telltale, that's for sure.

-Alan