Re: Dirty Snowball Worlds

Tim Little wrote:

> On 2008-02-22, Tux Wonder-Dog <wes.parish@[EMAIL PROTECTED]
> wrote:
>> (I confess I have always tied the Coriolis Effect to the fact that
>> Earth's angular velocity isn't synchronous with its orbital period.
>> I would be grateful for anyone to correct me on that.)
> 
> Coriolis effect is purely an artifact of a rotating coordinate system.
> In particular, it depends upon the *sidereal* day and not solar day.
> The confusion is probably not your fault - I've read a few physics
> textbooks that either don't make it clear or (occasionally) get it
> actually wrong.

Thanks!
> 
> 
>> If the orbit is nearly circular, the difference between the aphelion
>> and perihelion won't amount to much; if it is highly eccentric, it
>> won't be viable for Earth-standard life (or "life as we know it" ;)
>> On the other hand, it might well prove the "breath of life" for your
>> aliens - general overall torpor when the planet is at aphelion, time
>> to party when the planet is at perihelion.
> 
> Even a moderately eccentric orbit won't tide-lock 1:1. If such a
> planet were intially in 1:1 resonance, then at perihelion it will be
> rotating more slowly than it orbits, and thus tidal drag will act to
> speed up the rotation. At aphelion the reverse is true, but the
> slowing effect will be very much weaker due to the increased distance.
> 
> This is why Mercury is in a 3:2 resonance.

Thanks.  That makes sense.  Mind you, it does introduce additional
complications into the idea ... a planet in this situation we've been
discussing, with a moderately eccentric orbit and consequently a 3:2
resonance.  (Which does raise the question - is it likely that a planet so
close to its star, likely to be 1:1 tidally locked?  Dole thought it
likely, but most of the planets in so close that have been observed so
far,
have highly eccentric orbits, and the one we've been observing the
longest - Mercury - is in a 3:2 resonance tidal lock.  Now there's an M3
planet story or two I've had stashed away for 20 or so years that might
warrant a second look, and a much-needed rewrite ... ;)

Wesley Parish
> 
> 
> - Tim