[seqfan] Re: Another planetary sequence

[Rick Shepherd]

Regarding the original question, I'd just like to point out that many OEIS
sequences are time dependent, say, on how many days in an Earth year --
which will certainly change eventually. Also, many physical "constants" may
turn out not to be (in time and/or space) after more refined understanding
later. Nevertheless, snapshots of current understanding are definitely
useful.

A category of planet-related sequences of interest (in general to me, and
combinatorially) is number of types of planetary/star/moon orbital systems,
probably under various simplifying assumptions (the 3-body problem having
not been solved yet).

I have thought about such sequences several times over the last (10+?)
years, haven't submitted anything yet, but think they would be of
increasing general interest now that exoplanet discoveries have accelerated
markedly.

For simplicity, maybe start with counting all orbital situations that can
occur with all orbits elliptical and coplanar... Moons can have moons, etc.
Include rotations or not. Retrograde orbits or not. Well-defining
equivalence classes of orbital systems may be a bit tricky still.

(I'm deliberately ignoring Figure-8 orbits and such for now.)

Anyway, I think this is fertile ground (for the OEIS at least) for any
takers.

Best regards,
Rick