PLEASE NOTE:
*
Date sent: Wed, 04 Mar 1998 12:19:53 -0500 (EST)
From: Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject: CC DEBATE, 04/03/98
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
CAMBRIDGE-CONFERENCE DEBATE, 4 February 1998
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(1) MOON IMPACTS AND IMPACT RATES
Victor D. Noto vnn2@phoenixat.com
(2) MANY MOON IMPACTS & CRATERS TOO SMALL TO BE VISABLE BY
TELESCOPES
Simon Jeffery csj@star.arm.ac.uk
(3) 1-km IMPACT CRATER ON VISABLE FACE OF MOON EVERY 10,000 YEARS
David Morrison dmorrison@mail.arc.nasa.gov
(4) SMALL IMPACTS ON MOON EVERY ~30 YEARS
Alan W. Harris awharris@lithos.jpl.nasa.gov
==========================================
(1) MOON IMPACTS AND IMPACT RATES
From: Victor D. Noto vnn2@phoenixat.com
David
I can not think of a better experiment to test for impact rates
than to
put out a ball (the moon) about 1/4 the size of the Earth about
240
thousand miles into a stream of supposed rocks passing by our
planet
and look for how many impacts are made on that ball (the moon).
It does
not take too big a rock to make a fair size crater. Meteor crate
is
7/10 of a mile in diameter and the meteor was only 35 meters on
impact.
If we even took pictures of moon periodically, we should note
increased
numbers of craters showing up if the impact rate as high as even
twelve
a year. Did not the apollo astronauts leave a seimograph on the
moon
that could detect impacts on the moon? I think I remember that
they
did. So far I have not heard of or seen a picture of even a small
new
impact crater on the moon in 25 years. Not one picture - nothing.
So
far as I can tell there is no empirical data for impact rates
only
conjecture based on statistical data of the supposed number of a
given
size rocks in our near space.
Is there any empirical study which proves your figure of 100
fireballs
per year as you say?
Victor
================================
(2) MANY MOON IMPACTS & CRATERS TOO SMALL TO BE VISABLE BY
TELESCOPES
From: Simon Jeffery csj@star.arm.ac.uk
To: Victor D. Noto vnn2@phoenixat.com
Subject: Re: meteors hit moon regularly right?
Dear Victor
I am not an expert on this, but asking around I learnt the
following.
The earth is hit by about six 1 meter sized objects per year. The
gravitational cross-section of the moon is approximately 1/20th
of the
earth's, so the average impact rate on the moon would be about
one 1
meter class object every three years. However, craters formed by
objects of this size are too small too see with available
telescopes.
The youngest visible crater that we are aware of was formed about
1100
AD.
A boulder swarm hit the moon in 1975. It was detected by
seismometers
left behind by the Apollo missions. The experiment was turned off
later
that year.
I believe that the third fact provides the evidence you are
looking
for, but I cannot provide chapter and verse for the reference.
regards,
Simon Jeffery
--
Dr C Simon Jeffery email: csj@star.arm.ac.uk
WWW: http://star.arm.ac.uk/~csj/
Armagh Observatory, College Hill, tel: +44 1861 522928
Armagh BT61 9DG, Northern Ireland fax: +44 1861 527174
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(3) 1-km IMPACT CRATER ON VISABLE FACE OF MOON EVERY 10,000 YEARS
From: David Morrison dmorrison@mail.arc.nasa.gov
Victor:
I think that Simon Jeffery has given you a good response. There
are
lots of data from the lunar seismic experiments, from decades of
fireball surveys, and from the Defense surveillance satellites
that
define quite well the incidence of impacts in the
"fireball" range. It
is because of those data that we know the Lou Frank mini-comet
theory
is wrong. My only addition is to note that Jeffery's reference to
an
observed new lunar crater in 1100 is highly questionable and is
not in
fact widely accepted (although it has frequently been mentioned
as a
possibility).
Don't take my "100 fireballs" seriously -- the number
depends on how
you define a fireball. According to most definitions the number
is much
larger than 100 per year. At least a dozen of these are large
enough to
be detected from space, so the flux from the upper size end of
this
range is well determined. In contrast, we would expect a new 1-km
crater to form on the visible face of the Moon only about once
per
10,000 years -- not a practical way to measure the flux.
David Morrison
=============================
(4) SMALL IMPACTS ON MOON EVERY ~30 YEARS
From: Alan W. Harris awharris@lithos.jpl.nasa.gov
Dear Dave (and Victor),
I would add only that one of the five papers which recently
appeared in
GRL refuting Lou Frank's mini-comet hypothesis was in fact a
re-examination of the lunar surface in search of new craters.
Grier
and McEwen (Geophys. Res. Lett. 24, 3105-3108, 1997) examined 5.2
x
10^4 km^2 of lunar terrain which was imaged at high resolution by
both
the Apollo missions in the early 1970's and Clemintine in 1994.
If the
Lou Frank hypothesis were correct, they should see about 10,000
new
small craters in that area. They found none. This same survey
places an
upper limit on the actual rate of such impacts of around 30 per
year.
Keep in mind that this is only an upper limit based on zero
detections;
the real value is likely much, much less. They were considering
objects
of 5-10m diameter, which should make craters or at least bright
disturbances of the regolith at least 50 m in diameter. These
putative
objects are much larger than "fireball" size.
Cheers,
Al