[X] My Assistant

[SFJCody]

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

[dvandorn]

Truthfully, I think that Pluto needs to be demoted to a KBO, and the rest of these objects need to be classified as KBOs. Regardless of size and mass. I think it's obvious that the KBOs, as a class, were formed rather differently from the rest of what we think of as planets -- most specifically, since they do not orbit in the plane of the ecliptic, they could not have been formed primarily from the solar nebula, since those nebulae always seem to array themselves in fairly thin disks.

I think that planets should be defined as objects that accreted directly from the solar nebular disk (defined by its orbital inclination) *and* that are larger than "X" in size and/or mass. Everything else, regardless of size and/or mass, should be defined as a KBO or an Oort cloud object (OCO).

So, simple rule -- formed from within the planetary disk = planet, formed outside of the disk = other.

-the other Doug

[Alan Stern]

I think that planets should be defined as objects that accreted directly from the solar nebular disk (defined by its orbital inclination) *and* that are larger than "X" in size and/or mass. Everything else, regardless of size and/or mass, should be defined as a KBO or an Oort cloud object (OCO).

So, simple rule -- formed from within the planetary disk = planet, formed outside of the disk = other.


I'm sorry to say it, but this won't work etiher. I am on the IAU committee
looking into planetary nomenclature and one thing we defintiely agree on is
that formation mode is not a good way to go. Why? Because we won't
be able to determine an object's oriigin from things we observe-- this
problem is particularly acute for extrasolar planets.

And as to Sedna and Pluto and UB313, as best we can tell, they were accreted just
like Earth, Mars, etc., but aborted early in their growth. They were then ejected
to these oddball orbits, so in fact it does seem that these dwarf planets were
made just like Earth, and Mars, and Venus, but they ran out of feedstock for
one reason or another and ended up stunted.



And

[dvandorn]

Aw, shoot -- and here I had in mind a concept whereby these out-of-plane objects could be classified based on a certain degree of extra-solar composition. I had this image of the objects in the Kuiper Belt and Oort Cloud being condensed out of the interaction between the T-Tauri stage of the solar wind and the supernova remnant gasses and particles into which this energetic solar wind slammed... as such, they would be of a compositional mix between the solar nebula and the surrounding supernova nebula from which the Sun and its planetary nebula evolved.

Since the T-Tauri stage of the solar wind would have pushed out in all directions, it would have established a spherical structure around the Sun of the remnants of the interactions between the wind and whatever it pushed into and through on its way out. That would seem to be the perfect structure from which to derive the KBOs and OCOs, would explain why they occupy a space defining a spherical cloud around the Sun, and would suggest that these objects might be of somewhat different composition from the rest of the solar system.

Granted, all of this extrasolar material ought to similar to the materials derived from the planetary nebula, since the solar system was formed from a piece of the original supernova nebula. But it was my thinking that the extrasolar gasses and ices included in the KBOs and OCOs could let us characterize differences between the planetary nebula (from which the solar system was derived) and the surrounding supernova remnants. Isotopic abundance information would be extremely interesting, I bet...

But if all of these objects were originally formed from the planetary nebula disk and were later ejected into this spherical cloud, then my theory is non-applicable... darn it!

-the other Doug