On Sat, 25 Jul 2009 09:02:35 -0700 (PDT), Frogwatch
wrote:

On Jul 25, 11:21Â*am, Wayne.B wrote:
On Sat, 25 Jul 2009 11:07:30 -0400, Wizard of Woodstock

wrote:
I was testing my super secret helium ion powered mass driver. Â*I
didn't have it sighted in properly.

Jeeze - so I have a few bugs to work out - give me a break.

Don't point it at anyone unless you intend to shoot! Â*You could
vaporize the entire state of Maryland with one little slip. Â* :-)

I always wondered if the earths moon protected earth from otherwise
getting its share of impacts. Consider, the center of mass of the
earth-moon system is actually 1000 miles closer to the surface due to
the moon thus effectively reducing the earths radius by 1000 miles (a
drop in x sectional area of about 25%). Some people mistake the ratio
of the solid angle subtended by the moon as seen from earth to the
solid angle of the sky (2*pi) as being the reduction leading to a very
small diff, however, this is incorrect. The effective drop in area of
earth seen by an incoming asteroid is the ratio of earths x sectional
area using the effective radius with the moon to the area without the
moon.
This drop of 25% might be just what civilization needs to allow enough
time to get going before we can stop such impacts. Thus, an earth
without a large moon might not allow a civilization to develop.
The reverse situation is not true. That is, a large primary body
(uninhabited) with a small earth sized body with animals on it would
be in a poor position to develop civilization. Consider the moons of
Jupiter. Jupiter draws the crap in and then a lot of it hits the poor
moons, they are pocked with craters in spite of constant rearangement
of their crusts (look at Europa).
I once tried to write a program to simulate this but I ran out of
time. Then I tried to get my kids to do it for a science fair
project, no interest. Older daughter is about to graduate from
college with degree in bio so maybe I can convince
her......unfortunately, she has no knowledge of programming or
interest in orbital mechanics (its just vectors).

I thought most of those space rocks come bulleting through at +30k
mph. I suspect earth's gravitational pull has little effect on where
they hit. But I'm not a scientist, just a guesser.

--Vic