[TML] Bigass Planet X

[Jerry W Barrington]

On 11/19/07 7:55 PM, Steve Burchett wrote:

> I remember being taught Bode's Law in my youth. I wonder if it is still
> valid?

It not a "Law", as such.  Systems do seem to have roughly that sort of
structure, but with different relations between the orbits and lots of
exceptions.  Mostly it's a result of orbital resonance, and planets
"clearing" their neighborhoods.

And by systems, I include the system of planets, and the moon systems of
some planets.

As Eris pointed out, the "standard" Traveller orbits use the Bode Law,
extended outward.  Plus the possibility of a few loose "intermediate"
orbits, which explains Neptune's "wrong" position.  But it's on an eccentric
orbit which crosses Pluto's.

I once devised a system that started from a random orbit in the habitable
zone and randomly went inward and outward.  I multiplied or divided by a
number that was constant (but randomly generated) for each system.  And
there was a chance of empty orbits.  I'd dig it out, but I'm now inclined to
use something like StarGen.  It starts with a star and generates the
planets' orbits, size, temperature, atmosphere, etc.  And if you write down
the seed number, you can always regenerate it from the program.  :)



On 11/19/07 7:55 PM, Timothy Little wrote:

> What does this do to the distribution of objects that *do* qualify as
> being planets rather than large belt objects?  I don't think we can
> know, yet.  We only have a census of planets in one system, and no
> idea whether the conditions here were typical.

That's why we need to look not at our own system, but at the products of
reasonable simulations.

We know gas/dust clouds exist, we can observe them.
We know from physics how such a cloud should collapse into roughly a disk.
Then it is a matter of making different assumptions about how such a disk
accretes into larger objects.  All the simulations I have seen make systems
*roughly* like the aforementioned StarGen, leading to the thought that real
systems should look *roughly* like that.  Incidentally, the overall shape is
similar to our Solar System, but with great variation: small rocky bodies
close to the star, progressing to gas giants, then to smaller rocky/icy
bodies.  This is due to mass distribution and to stellar radiation.