Phil Hays wrote:
> On Sun, 2010-01-03 at 09:27 -0800, Alastair wrote:
>
>> Hansen seems to believe that Venus had oceans, but that is now seeming
>> unlikely. It is now thought that Earth's oceans were formed from
>> impacts from Main Asteroid Belt Comets.
>> http://www.solstation.com/stars/asteroid.htm
>> These are icy outer asteroids which had there orbits distorted by
>> Jupiter. As their orbits became more elliptical, they collided with
>> Earth, which protected Venus and kept it dry. The runaway state of
>> Venus's atmosphere must be due to CO2, not H2O!
>
> A scale model might help to visualize.
>
> If the Earth is a peppercorn, then the Sun is a 20 cm ball about 26
> meters away. Get a peppercorn and a ball, and make a scale model of the
> Earth/Sun system. If you please, you could also add Venus another
> peppercorn 19 meters from the Sun, and the Earth's Moon, a bit of gravel
> 2 cm away from the Earth. Now imagine that there are comets coming from
> the outer solar system, in the neighborhood of Jupiter, another 110
> meters beyond the Earth.
>
> Just how many of these comets will the Earth prevent from hitting Venus?
>
>
I don't know much about planetary evolution, but I've read enough to
know that there are some pretty counterintuitive (to me) things going
on, mostly due to the amazingly long time scales involved.
In this case it doesn't seem too implausible that if the comets are
slowly nudged into increasingly elliptical orbits, they will almost
invariably get caught by the Earth before the orbit becomes sufficiently
distorted to reach Venus. But I'm just guessing really.
James
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