PLEASE NOTE:
*
Date sent: Thu, 05 Mar 1998 16:06:26 -0500 (EST)
From: Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject: CC DEBATE, 05/03/98
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
CAMBRIDGE-CONFERENCE DEBATE, 5 MARCH 1998
----------------------------------------
(1) LUNAR IMPACT RATE FAR HIGHER: 815 METEORITE IMPACTS AND TWO
METEOR STORMS RECORDED ON MOON IN JUST OVER TWO YEARS
Peter Grego PeterGrego@compuserve.com
(2) IMPACT FREQUENCY CONTROVERSY DIVERTS ATTENTION FROM REAL
PROBLEM
Bob Kobres bkobres@uga.edu
=====================================
(1) LUNAR IMPACT RATE FAR HIGHER: 815 METEORITE IMPACTS AND TWO
METEOR STORMS RECORDED ON MOON IN JUST OVER TWO YEARS
From: Peter Grego PeterGrego@compuserve.com
Lunar Section Director, Society for Popular Astronomy
In reply to, and to expand on impact matters lunar....
1. A 12th Century Minor Asteroid Impact on the Moon's far-side?
The supposed AD 1100 lunar impact mentioned by Simon Jeffery and
David Morrison I think refers to a remarkable event in AD 1178
chronicled by Gervase, a 12th century monk whose chronicle is
preserved in the library of Trinity College, Cambridge. On 18
June
(old calendar) in the year 1178, a group of men at Canterbury in
England were admiring the beautiful four-day-old crescent Moon on
that warm summer's evening, Gervase reports them to have been
startled by "a flaming torch" which suddenly appeared
at
the lunar limb, "spewing out, over a considerable distance,
fire,
hot coals and sparks." The Moon is said to have
"writhed like a
wounded snake" and assumed a blackish appearance shortly
after this
unprecedented occurrence.
It is now thought by some that the 1178 event was caused by a
sizeable meteoritic impact upon the lunar surface. As such, it
was
the first of only two major cosmic impacts to have been observed
this millennium - the other one happened in July 1994 with the
impacts of comet Shoemaker-Levy's fragmented nucleus in the
atmosphere of Jupiter. It is ironic that both the 1178 and 1994
events were situated just past the limb of the impacted object,
making it impossible to directly observe the site of the impacts
at
the moment they occurred.
From the rough position of the "flaming torch"
described in the
chronicle, Jack Hartung of New York University in the 1970s
worked
out that the impact site lay at around 45 north and 90 east.
Looking at photographs taken by spacecraft in lunar orbit, the
site
became seemingly obvious - a bright, fresh-looking 20 km diameter
crater called Giordano Bruno, situated just past the lunar limb
(36
N, 103 E) and surrounded by a prominent system of rays. Some of
these rays actually extend past the mean limb around onto the
near-side, so they are theoretically visible through binoculars
and
telescopes. Bruno and its rays may represent the newest major
topographical features on any body in the solar system which are
likely to be permanent.
I have tried looking for Bruno's rays - binoculars are best
suited
to this task. Indeed, on viewing with a good lunar libration and
phase there is some limb brightening on the northeast edge of the
Moon, and some faint streaks on the dark Mare Crisium that may
actually represent the Bruno ejecta system.
2. Lunar Impacts
High temperatures are formed at the lunar surface when
fast-moving
objects impact with the Moon, converting kinetic energy to heat.
Some of the short-lived flashes which have been telescopically
observed through the centuries are likely to have been caused by
small meteoroidal impacts. Material thrown up by the impact would
form into an expanding shell of dust and rock which may be
visible,
especially if the focus of impact happens to lie just beyond the
terminator and the column of ejecta climbs high enough to be
illuminated by the sun. However it has not been proven that any
TLP
flash site has ever yielded a new crater which has been detected
from the Earth.
The most credible telescopic observation of a lunar impact seems
to
have been that of the 501 kg spaceprobe Luna 5 on 12 May 1965 as
it
smashed into Mare Vaporum (31S 8E). A cloud of "lunar
dust"
measuring 225 x 80km was reported by astronomers at the German
observatory at Rodeswich. The resultant crater is too tiny to be
resolved with Earthbound instruments.
3. Moon impactors detected by Apollo seismometers
The four Apollo lunar seismometers detected tremors in the Moon's
crust. Some of the vibrations recorded were due to deep
moonquakes,
but many were likely to have been caused by the impact of
meteoroids
on the Moon's surface. It was possible to estimate roughly where
each meteoroid had landed and the force of impact. In a 2.5 year
period commencing in 1973, most of the 815 recorded meteoroid
impacts were randomly distributed. But on three occasions -
November
and December 1974 and June 1975 - the Moon seems to have ploughed
through a dense barrage of large meteoroids.
Peter Grego
Lunar Section Director, Britain's Society for Popular Astronomy
PeterGrego@compuserve.com
========================
(2) IMPACT FREQUENCY CONTROVERSY DIVERTS ATTENTION FROM REAL
PROBLEM
From: Bob Kobres bkobres@uga.edu
I still find it amazing that people continue to bog-down with
discussion of impact frequency as if that was really a factor in
the
decision of whether or not we will build a credible defense
against
the exceptional broadly lethal event. The bottom line is that a
major impact would do in our way of life and it now seems
feasible
to prevent such an unfortunate occurrence. It does not matter if
we
construct a defense system that could adequately protect us
presently and find latter that we would have been fine for a
thousand more trips about the Sun without the protection. What
will
matter is learning of an imminent threat with an interval to
impact
less than the time required to enable a viable defense.
This, I feel, is the message that is not getting through to key
decision makers. The stakes are simply too high to gamble when
there
is no good reason (IMHO) for us to postpone the development of a
defense system.
Perhaps that’s where the debate needs to focus. What are the
pros
and cons of developing an Earth Defense System as soon as
possible?
bobk
Bob Kobres
bkobres@uga.edu
http://abob.libs.uga.edu/bobk
706-542-0583
Main Library
University of Georgia
Athens, GA 30602
*
Date sent: Thu, 05 Mar 1998 15:53:20 -0500 (EST)
From: Benny J Peiser B.J.PEISER@livjm.ac.uk
Subject: CC DIGEST, 05/03/98
To: cambridge-conference@livjm.ac.uk
Priority: NORMAL
CAMBRIDGE-CONFERENCE DIGEST, 5 MARCH 1998
-----------------------------------------
(1) MARTIAN METEORITE SAMPLES ON OFFER TO RESEARCHERS
Ron Baalke BAALKE@kelvin.jpl.nasa.gov
(2) METEOR LUMINOSITY FROM OBSERVATIONS OF LEONID METEORS
Y. Fujiwara et al., NIPPON METEOR SOCIETY
(3) RADIANT DISTRIBUTION OF METEOROIDS ENCOUNTERING THE EARTH
A.D. Taylor et al., UNIVERSITY OF ADELAIDE
(4) HEIGHT DISTRIBUTION OF METEORS AND IMPLICATIONS FOR METEOROID
CHEMISTRY
W.G. Elford et al., UNIVERSITY OF ADELAIDE
(5) REFERENCES FOR RAMPINO'S PAPERS ON THE SHIVA HYPOTHESIS
Benny J Peiser b.j.peiser@livjm.ac.uk
======================================================
(1) MARTIAN METEORITE SAMPLES ON OFFER TO RESEARCHERS
From: Ron Baalke BAALKE@kelvin.jpl.nasa.gov
Antarctic Meteorite Newsletter
February 1998
Nakhla To Be Distributed
By Dr. Monica Grady
Natural History Museum, London
Nakhla is a 1300 million year old Martian meteorite, the first
one
in which carbonates were identified. Nakhla fell as a shower of
stones in 1911; several of the stones are in the collection of
the
Natural History Museum in London.
One completely fusion-crusted stone has been kept unbroken since
its
acquisition in 1913.
The Natural History Museum is now prepared to offer samples of
this
stone to scientists for appropriate analyses. The Antarctic
Meteorite Processing Group had kindly agreed to allow the stone
to
be broken and sub-divided at the Curatorial Facility at the
Johnson
Space Center in Houston, prior to the LPSC in March.
There is no formal deadline for sample requests, but the material
available is limited. Coordinated approaches from groups of
scientists undertaking complementary studies are encouraged.
Those
requests submitted to the Museum by April 3 will be processed in
April. Those arriving later will be delayed for several months.
For further details and to submit requests, contact:
Dr. Monica M. Grady
Dept. of Mineralogy
The Natural History Museum
Cromwell Road
London SW7 5BD
E-Mail: mmg@nhm.ac.uk
=====================================
(2) METEOR LUMINOSITY FROM OBSERVATIONS OF LEONID METEORS
Y. Fujiwara*), M. Ueda, Y. Shiba, M. Sugimoto, M. Kinoshita,
C. Shimoda, and T. Nakamura: Meteor luminosity at 160 km altitude
from TV observations for bright Leonid meteors. GEOPHYSICAL
RESEARCH
LETTERS, 1998, Vol.25, No.3, pp.285-288
*) NIPPON METEOR SOCIETY, 2-16-8 MIKUNI HONMACHI, OSAKA 532,
JAPAN
Two atmospheric trajectories have been determined by simultaneous
observations with image intensifier-fitted TV cameras and
conventional photographic cameras for two bright Leonid meteors
(fireballs) in 1995 and 1996. Beginning heights recorded by the
photographic method are lower than about 130 km, but those
observed
by the TV systems are closer to 160 km. The primary reason for
this
difference is the sensitivity of the observing systems. However,
the
difference in the sensitive wavelengths (up to 900 nm for the TV
systems) could be another factor contributing to the large
difference between the two methods. This suggests that the
beginning
heights of high speed bright meteors such as Leonid meteors are
much
higher than previously thought. Copyright 1998, Institute for
Scientific Information Inc.
====================================
(3) RADIANT DISTRIBUTION OF METEOROIDS ENCOUNTERING THE EARTH
A.D. Taylor: Radiant distribution of meteoroids encountering the
Earth. ADVANCES IN SPACE RESEARCH, 1997, Vol.20, No.8,
pp.1505-1508
UNIVERSITY OF ADELAIDE, DEPARTMENT OF PHYSICS & MATHEMATICAL
PHYSICS, ADELAIDE, SA 5005, AUSTRALIA
The radiant distribution of meteors detected during the Harvard
Radio Meteor Project, 1968-69, Synodic Year Program have been
reanalysed to remove selection effects associated with the radar
observations. Corrections are made for the observing schedule;
antenna beam patterns, the radio diffusion ceiling, speed
dependence
of ionization production and the flux enhancement due to the
Earth's
gravity. These give the radiant distribution for meteoroids
larger
than 10(-4) g encountering the Earth; The dominant concentrations
come from the so-called Helion and Antihelion sources, with peak
fluxes 6-8 times that of the background. The radiant distribution
expected for impact craters larger than a given diameter is
provided
for comparison with spacecraft observations. For these conditions
the Apex and Toroidal sources also becomes significant. (C) 1997
COSPAR. Published by Elsevier Science Ltd.
===============================
(4) HEIGHT DISTRIBUTION OF METEORS AND IMPLICATIONS FOR METEOROID
CHEMISTRY
W.G. Elford, D.I. Steel, and A.D. Taylor: Implications for
meteoroid
chemistry from the height distribution of radar meteors. ADVANCES
IN
SPACE RESEARCH, 1997, Vol.20, No.8, pp.1501-1504
UNIVERSITY OF ADELAIDE, DEPARTMENT OF PHYSICS & MATHEMATICAL
PHYSICS, ADELAIDE, SA 5005, AUSTRALIA
We have gathered substantial evidence from novel radar meteor
observations that most meteoroids start to ablate at altitudes
considerably in excess of 100 km (at heights up to similar to 140
km). This beginning height ha is a strong function of the melting
point of the meteoroid. Theoretical modelling indicates that for
stony meteoroids observed as faint radio meteors these heights
range
from hb = 116km (for entry speeds v(infinity) = 70 km s(-1)) to
90
km (for v(infinity) = 15 km s(-1)). Meteoroids that begin
ablating
above these heights must have lower temperature melting points.
We
interpret the observations in terms of a population of the
meteoroids largely constituted of heavy organic compounds that
are
susceptible to gross-fragmentation as they heat and encounter the
Earth at speeds greater than similar to 30 km s(-1).
==========================
(5) REFERENCES FOR RAMPINO'S PAPERS ON THE SHIVA HYPOTHESIS
From: Benny J Peiser b.j.peiser@livjm.ac.uk
I recently circulated the abstract of Mike Rampino's recent paper
on
the Shiva Hypothesis but forgot to include the reference. The
paper
in question was published in the current issue of The Planetary
Report, Vol. 18, No. 1, p. 6-11 (1998).
A longer, technical version can be found in: Earth, Moon and
Planets,
v. 72, p. 441-460 (1996). You may also be interested in: Rampino,
M.
R.,1991, Shiva versus Gaia: Cosmic Effects on the Long-Term
Evolution
of the Biosphere: in Scientists on Gaia, ed. S.H. Schneider and
P.
Boston, MIT press, Cambridge Mass, p. 382-391.
===============================================
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