Re: poly: Re: the Moon and life on Earth

At 01:46 AM 1/20/98 EST, Curt wrote:

>the moon stabilizes the Earth's axis of rotation. Without that
>stabilization the axis drifts widely over time, including sometimes
>tilting at 90 degrees like Uranus right now

Well, Saturn's and Neptune's tilts are close to our own (26.73 degrees and
28.8, cf. 23.45), and they have some hefty moons.

Moonless Mercury is only 7.0.

Then again I guess *some* planet's equator is likely to be close to the
ecliptic at any given time. It's true that the Uranian moons only amount
to a bit more than a tenth the mass of the Moon, for a primary 14-something
times massier than Earth.

I find in Ivars Peterson's popularisation NEWTON'S CLOCK: CHAOS AND THE
SOLAR SYSTEM (1993):

`In Earth's case, the moon acts as a stabilizing influence... forces the...
precession... at a sufficiently rapid rate to forestall wildly erratic
variations in Earth's tilt. [26K year precession is] rapid enough to keep
it out of the range of chaos-triggering resonances with other motions in
the solar system.. Thus the moon may play a crucial role in regulating
Earth's climate, stabilizing it enough... for the evolution of life.' [So
big Moons would be necessary for life elsewhere, as Curt points out]

[Effectively moonless Mars, by contrast, experiences] `large irregular
oscillations that cause dips as large as 50 or 60 degrees in the tilt angle.'

[This could happen to Earth when the receding Moon] `reaches 68 Earth radii
in a few billion years. (The present day distance is about 60 Earth
radii.)' (pp. 269-270)

Damien Broderick
Received on Wed Jan 21 00:39:44 1998