PLEASE NOTE:
*
CCNet, 18 October 1999
------------------------
(1) SOME MINOR BODIES NEWS FROM THE DPS MEETING IN PADOVA
Daniel Fischer <dfischer@astro.uni-bonn.de>
(2) POTENTIAL MEGAIMPACT-VOLCANIC CONNECTIONS
Andrew Glikson <geospectral@spirit.com.au>
(3) CRATERS, GEOLOGICAL BOUNDARIES & ERUPTIONS
Michael Paine <mpaine@tpgi.com.au>
(4) GREEN PLANET OR DESERT WORLD?
Andrew Yee <ayee@nova.astro.utoronto.ca>
(5) EVE OF DESTRUCTION
Kasra Maasumi <kasra138@hotmail.com>
(6) GRAVITATIONAL EFFECTS AFTER IMPACT DISRUPTION OF A MINOR BODY
G. DAbramo*), A. DellOro, P. Paolicchi,
UNIVERSITY OF PISA
==========
(1) SOME MINOR BODIES NEWS FROM THE DPS MEETING IN PADOVA
From Daniel Fischer <dfischer@astro.uni-bonn.de>
Dear Benny,
since there haven't been any reports here so far on the large
(800
participants!) Meeting of the Division of Planetary Sciences in
Padova
teh past week, except for a few press releases, let me point
those
interested to the Cosmic Mirror # 152 - available at
http://www.astro.uni-bonn.de/~dfischer/mirror/152.html
- where I
posted small and large stories from the conference on a daily
basis. Of
specific interest for the minor bodies community are:
- vague plans to repeat the Lunar Prospector crash on the
Moon (that yielded absolutely zero measurable
effect)
with a larger spacecraft,
- first insights into what NASA ponders in interplanetary
missions more than a decade ahead (a comet
nucleus
sample return has once more high priority),
- renewed interest in Russia in a Phobos sample return
mission and a sample return from asteroid
Fortuna (though
it is questionable whether the commitment goes
beyond the
current study stage),
- radar data (just a few days old) from asteroid 1999 TY2
which may be an even faster rotator than 1999
KY26,
- plans for groundbased observations of the two 2001
targets of Deep Space 1, the dead comet W-H
and
the active comet Borrelly,
- and the first prediction what will happen to comet
Tempel 1 when the Deep Impact bullet hits it
in 2005.
Other memorable aspects of the huge meeting: Many talks in the
NEO
session repeated precisely that what has been said and explained
on
CCNet about impact probabilities, NEODyS, keyholes and so on -
this
left the impression with me that CCNet discussions actually
*represent*
the current state of the field. On the technical front it was
surprising (or maybe not) in how many different areas of
planetary
science the best data come from operational Adaptive Optics
systems
these days, be it the celebrated discovery of Eugenia's
moon or
highly detailled images of Io, Titan or Neptune.
There was also a bizarre feud going on during the meeting between
a
columnist of the Planetary Report who has misread a JPL Press
Release
of July 29th (that correctly claimed that Deep Space 1 had
achieved
100+ percent of its objectives which were *technological* in
nature)
and had published some provocative remarks about it which he
repeated
on stage now during the opening ceremonies. Plus he speculated
about a
conspiracy by NASA to silence him and to hide the truth about
DS1's
glitches during the Braille encounter (wrong again: the
respective
Rayman Mission Log is still on the DS1 web site, at
http://nmp.jpl.nasa.gov/ds1/mrlogP.html).
Later during a special
session, a leading DS1 scientist rebutted the vicious attack by
presenting excerpts from his personal correspondence with said
columnist - another somewhat unusual procedure for a scientific
conference that otherwise went along in a more peaceful fashion
in the
beautiful (if somewhat foggy) environment of Northern Italy.
Daniel Fischer, science writer, Germany
============
(2) POTENTIAL MEGAIMPACT-VOLCANIC CONNECTIONS
From Andrew Glikson <geospectral@spirit.com.au>
Dear Benny,
With reference to communications by T. Assmuth and M. Paine
(CCNet
14.10.99) - I append the abstract of a relevant article: Oceanic
mega-impacts and crustal evolution (May 1999, Geology 27:387-341)
and references to earlier papers which discuss this question.
I will add that the likely burial of oceanic craters by volcanic
extrusions and sediment fill complicates the search for these
structures, except by detailed and expensive deep ocean seismic
reflection studies.
Andrew Glikson
15 October, 1999
----------------------
Oceanic mega-impacts and crustal evolution
(Glikson, A.Y., Geology 27:387-341)
ABSTRACT
Lunar mare crater counts, the terrestrial impact flux, and
astronomical observations of asteroids and comets define a
consistent impact rate of 4-6 * 10-15 km-2.yr-1 within the inner
solar system since the end of the Late Heavy Bombardment (LHB)
~3.8 Ga ago. Coupled with the observed crater size vs cumulative
crater size frequency relationship of N * Dc-1.8 (N = cumulative
number of craters of diameter > Dc), these rates imply
formation
on Earth of more than 450 Dc * 100 km-diameter craters, more than
50 Dc * 300 km-diameter craters, and more than 20 Dc * 500
km-diameter craters. Geochemical and isotopic constraints require
that more than 80% of the projectiles impacted on time-integrated
oceanic crust since the LHB. The injection of shock energies
calculated at >108 megatons TNT-equivalent by a Dp > 10
km-diameter projectile may result in propagating fractures and
rift networks, thermal perturbations, and ensuing magmatic
activity. Examinations of the geologic record for correlated
impact and magmatic fingerprints of such events remain
inconclusive in view of isotopic age uncertainties. Potential but
unproven connections may be represented by the (1)
Cretaceous-Tertiary boundary (ca. 65 Ma) impact(s), onset of the
Carlsberg Ridge spreading, Deccan volcanism, and onset of the
mantle plume of the Emperor-Hawaii chain; (2) Jurassic-Cretaceous
boundary (ca. 145 Ma) impacts, onset of Gondwana breakup,
including precursors of the east African rift structures; (3)
Permian-Triassic boundary (ca. 251 Ma) impact(s), Siberian
Norilsk
traps, and early Triassic rifting; and (4) the 3.26 Ga basal Fig
Tree Group (east Transvaal) Ir-rich and Ni-rich quench
spinel-bearing impact spherules and contemporaneous
igneous-tectonic activity. Tests of the theory require further
identification and isotopic dating of distal ejecta, impact
spherule condensates, and meteoritic geochemical anomalies.
selected references
Alt, D., Sears, J. M., and Hyndman, D. W., 1988, Terrestrial
maria: the origins of large basalt plateaus, hot spots tracks and
spreading ridges: Journal of Geology, v. 96, p. 647-662;
Coffin, M. F. and Eldholm, O., 1994, Large igneous provinces:
crustal structure, dimensions and external consequences: Reviews
of Geophysics, v. 32, p. 1-36.
Gersonde, R., Kyte, F. T., Bleil, U., Diekmann, B., Flores, J.
A.,
Gohl, K., Grahl, G., Hagen, R., Kuhn, G., Sierro, F. J., Volker,
D., Abelmann, A., and Bostwick, J. A., 1997, Geological record
and
reconstruction of the late Pliocene impact of the Eltanin
asteroid
in the Southern Ocean: Nature, v. 390, p. 357-363.
Glikson, A. Y., 1993, Asteroids and early Precambrian crustal
evolution: Earth-Science Reviews, v. 35, p. 285-319.
Glikson, A. Y., 1996, Mega-impacts and mantle melting episodes:
Tests of possible correlations: Australian Geological Survey
Organisation Journal of Australian Geology and Geophysics, v. 16,
part 4, p. 587-608.
Hughs, H. G., App, F. N., and McGetchin, T. N., 1977, Global
seismic effects of basin-forming impacts: Physics of the Earth
and
Planetary Interiors, v. 15, p. 251-263.
Jansa, L. F., 1993, Cometary impacts into ocean: Their
recognition
and the threshold constraints for biological extinction:
Palaeogeography, Palaeoclimatology, Palaeoecology, v. 104, p.
271-286.
Jones, A. G., 1987, Are impact-generated lower crustal faults
observable?: Earth and Planetary Science Letters, v. 85, p.
248-252.
Oberbeck, V. R., Marshall, J. R., and Aggarval, H., 1992,
Impacts,
tillites and the breakdown of Gondwanaland: Journal of Geology,
v.
101, p. 1-19.
Roddy, D. J., Schuster, S. H., Rosenblatt, M., Grant, L. B.,
Hassig, P. J., and Kreyenhagen, K. N., 1987, Computer simulation
of large asteroid impacts into oceanic and continental sites -
Preliminary results on atmospheric, cratering and ejecta
dynamics:
International Journal of Impact Engineering, v. 5, p. 525-541.
Andrew Glikson
Research School of Earth Science
Institute of Advanced Studies
Australian National University
Canberra ACT 0200 Australia
andrew.glikson@anu.edu.au
<mailto:andrew.glikson@anu.edu.au>
==================
(3) CRATERS, GEOLOGICAL BOUNDARIES & ERUPTIONS
From Michael Paine <mpaine@tpgi.com.au>
Dear Benny,
Andrew Glikson sent me some extra data about impacts and
eruptions.
I have prepared a graph of the information at:
http://www1.tpgi.com.au/users/tps-seti/crater.html
It shows up some interesting "co-incidences"! By the
way, the version
of my Explorezone article "How an asteroid impact causes
extinction"
that was published in CCNet contained an error, the number of
known
Earth impact structures is "more than 150" (159
according to NRC) not
250!
Michael Paine
=================
(4) GREEN PLANET OR DESERT WORLD?
From Andrew Yee <ayee@nova.astro.utoronto.ca>
[http://helix.nature.com/nsu/991021/991021-1.html]
Friday, October 15, 1999
Green planet or desert world?
By PHILIP BALL
For those who have wondered what life would be like on the alien
planets of the Star Wars films, a study conducted at the
University of
Hamburg, Germany, should now assuage your curiosity. But Klaus
Fraedrich and colleagues at Hamburg's Meteorological Institute
are not
conducting idle speculation about would-be worlds -- their work
casts
light on the role that vegetation plays in the Earth's climate
system.
Attempts to simulate our planet's climate using computer models
are now
routine. But mostly these start out with a planet that closely
resembles the present-day Earth, for example to investigate how
it
might change in the face of such disturbances as human-induced
global
warming. Fraedrich and colleagues have done something more
extreme.
They consider an Earth on which the land masses support the
maximum
amount of vegetation conceivable -- like the Forest Moon of Endor
in
The Return of the Jedi -- and one in which all the land is a
barren
desert, as Luke Skywalker's homeworld of Tatooine.
Whether or not the world has ever been as green as the Hamburg
group's
"Green Planet", there have certainly been times in the
past when the
global climate was warmer and wetter, and the vegetation more
abundant.
And before life colonized the land, this was surely a planet
something
like the researchers' "Desert World". Desert conditions
do not imply a
hot climate, however -- the Siberian and Mongolian steppes are
partly
frigid deserts.
Fraedrich and colleagues are not, however, anticipating a return
to
these extremes -- at least, not in the near future. Rather, they
chose
to model them so that the effects of land plants on climate would
be
seen as clearly as possible. The insights thus gathered might
then be
applicable to regions where, for instance, vegetation is
disappearing
due to deforestation (in Brazil) or encroachment of deserts (in
northern Africa).
Plants are not just the beneficiaries but the engineers of a
moist
climate. Trees pump vast amounts of water up from their roots to
their
leaves, where much of it is lost by evaporation. This process,
called
transpiration, allows a typical birch tree to pump around 80
gallons of
water each day from the ground into the atmosphere. In addition,
plants
help to maintain the porous structure of soil and so to retain
rainwater. And they prevent soils from being rapidly eroded away
by
running water after heavy rain.
In this way, vegetation plays a crucial role in the cycling of
water
from sky to ground and back again -- the so-called hydrological
cycle.
And indeed Fraedrich and colleagues found that there was much
more
intense cycling of water on their Green Planet relative to Desert
World; the climate was wetter. But a wetter world should mean
more
cloud cover, and that in turn could increase the amount of
sunlight
reflected back to space, cooling the globe.
The researchers found that this cooling effect was almost
balanced out
by a warming influence resulting from the covering of bare ground
by
plants. Because plants are darker than dry desert,
vegetation-covered
land surface absorbs more of the Sun's heat than does the desert
surface.
Because its atmosphere was more moist, the Green Planet also had
more
intense storms and monsoons than the Desert World -- cyclone
systems,
for instance, are triggered initially by the condensation of
water
vapour. But temperatures at the surface of the Green Planet are
overall
slightly lower than those on Desert World, partly because
evaporation
of water pumped up by plants sucks in heat.
Although the German study, described in the October issue of the
Journal of Climate [1], uses a highly simplified model of the
interactions between climate and vegetation, it gives a
broad-brush
picture of the changes that we might expect if we continue to let
the
"desert" replace the forest.
[1] Fraedrich, K., Kleidon, A., Lunkeit, F. A Green Planet versus
a
Desert World: Estimating the Effect of Vegetation Extremes on the
Atmosphere. Journal of Climate 12, 3156-3163 (1999).
© Macmillan Magazines Ltd 1999 - NATURE NEWS SERVICE
=================
(5) EVE OF DESTRUCTION
From Kasra Maasumi <kasra138@hotmail.com>
Hi Benny,
I was reading the CCNet and coincidentally my bio-diversity
instructor
pointed out something in class that somehow I thought might be
related to the issue of "the origin of life." Well we
were talking
about the structure of the eukaryotic cells, cells of all
creatures
except the bacteria. These cells contain among other
membrane-bound
organelles Mitochondira. Mitochondria are the power plant of the
cell. They make the energy of the cell. More interesting the
mitoch.
have their own set of DNA. The cell's nucleus has one set of DNA
and
the mitochondria has also its own DNA. This is nothing new;
scientists compare two very related yet diverged spieces by
looking
at their Mitoch. DNA. The mitoch.DNA is also a mutation target
for
all kind of mutations. What the scientists do is compare the
mitoch.DNA of, for instance, the western wolf and the eastern
wolf and
look for missing DNA sequences of the western wolf in the
mitoch.DNA
of the eastern wolf. So where ever one sequence is missing in one
spiece they try to find it in the other one. Now the purpose of
this
is that by comparing and filling the spaces of mitoch. DNA the
scientists can build up the Mitoch.DNA of the ancester of the
wolves
and also the time they lived in. Scientists, of course, did this
whole
thing years ago and came to a fascinating conclusion: the
ancester of
today's humans leads to only one kind of sequence of DNA. This
means that it leads to only one person. This person was named
Eve,
hence the entire project was called the Eve project. So the
mother of
the entire human species today is considered to be that person.
This
was an African woman who lived circa 235,000 ya. Well, in
evolutionary
biology there is only one way by which evolution can occur. It is
called Random Genetic Drift, more precisely the Bottleneck
effect. Here
is how it works: Let's say the population of one kind of spiece
is
wiped out through a natural disaster from a million to a few
individuals. Now, if these few individuals revive and the
population
grows again, the gentic diversity is very small, because they
rose from
only a few individuals that did not represent the entire
population's
gentic diversity. Therefore, many attributes, shared by those few
individuals, will be very common among the new revived
population.
Back to the Eve project, the instructor pointed out that this
might
have happened 235,000 years ago. A natural disaster destroyed
almost
the entire human race on earth. Only a few remained, among which
Eve
survivied. She and a few males basically reproduced and after
235,000
years we have now six billion people on earth. What I wanted to
know
is: What happened or might have happened at that time?
As you British say - cheers.
Kasra
EDITOR’S NOTE: It is difficult to know what kind of natural
disaster/s
may have occurred at the time in question and whether or not it
contributed
to the well-known reduction of genetic diversity in humans.
However, an
interesting and related research report which I posted on the
CCNet, 9
September 1998, provides some possible trigger for global
catastrophes
that may indeed have had significant evolutionary knock-on
effects. It
should be stressed, nevertheless, that major climatic downturns
that
trigger Dark Ages and Ice Ages can also occur due to high-level
cosmic
dust loading. BP
-------------------
Ancient 'Volcanic Winter' Tied To Rapid Genetic Divergence In
Humans
University Of Illinois At Urbana-Champaign
http://www.admin.uiuc.edu/NB/98.09/Volcanic.html
September 1998
CHAMPAIGN, Ill. -- A new hypothesis about recent human evolution
suggests that a horrific "volcanic winter" 71,000
years ago, followed
by the coldest 1,000 years of the last Ice Age, brought
widespread
famine and death to modern human populations around the world.
The
abrupt "bottleneck," or decrease, in our ancestors'
populations, in
turn, brought about the rapid "differentiation" - or
genetic
divergence - of the surviving populations..
The hypothesis, offered by anthropologist Stanley Ambrose of the
University of Illinois, proposes that a volcanic winter reduced
populations to "levels low enough for evolutionary changes,
which
occur much faster in small populations, to produce rapid
population
differentiation," Ambrose said. If, as he believes, the
eruption of
Mount Toba in Sumatra caused the bottleneck, "then modern
human races
may have diverged abruptly, only 70,000 years ago," Ambrose
wrote in
the June issue of the Journal of Human Evolution.
Geneticists long have argued that the human species passed
through a
recent bottleneck, but they never offered explanations for the
population crash or recovery, nor considered its consequences for
modern human diversification. Ambrose's model, which he calls the
Weak
Garden of Eden/Volcanic Winter model, is an offshoot -
with
significant additions - of the Weak GOE model proposed by Henry
Harpending and others. The Weak GOE model proposes an African
origin
for modern humans about 130,000 years ago, and credits the
invention
and spread of advanced stone tool technology, 40,000 to 50,000
years
ago, for population growth after the bottleneck. Ambrose argues
that
volcanic winter resulting from the super-eruption of Toba
"caused the
bottleneck, and that populations may have expanded in response to
climatic warming 10,000 years before the advent of modern
technology."
Ambrose has linked geneticists' research to that of
volcanologists Michael
Rampino, Stephen Self, Greg Zielinski and colleagues, which shows
the
super-eruption of Toba caused a volcanic winter that lasted six
years
and significantly altered global climate for the next 1,000
years.
Those six years of "relentless volcanic winter" led to
substantial
lowering of global temperatures, drought and famine, and to a
global
human population crash during which, if geneticists are correct,
no
more than 15,000 to 40,000 people survived.
"The standard view of human evolution has been that modern
populations
evolved from an ancient African ancestor. We assumed that they
differentiated gradually because we assumed ancestral populations
were
large and stable," Ambrose said. But, he noted, genetic
research now
demonstrates that changes in population size were
sometimes
dramatic. The new model resolves the paradox of the recent
African
origin model: If we are all so recently "out of
Africa," why don't we
all look like Africans?
"When our African recent ancestors passed through the prism
of Toba's
volcanic winter, a rainbow of differences appeared," Ambrose
said.
=============
(6) GRAVITATIONAL EFFECTS AFTER IMPACT DISRUPTION OF A MINOR BODY
G. DAbramo*), A. DellOro, P. Paolicchi: Gravitational effects
after the
impact disruption of a minor planet: geometrical properties and
criteria for the reaccumulation. PLANETARY AND SPACE SCIENCE,
1999,
Vol.47, No.8-9, pp.975-986
*) UNIVERSITY OF PISA,DIPARTIMENTO FIS,PIAZZA TORRICELLI
2,I-56127
PISA,ITALY
After the catastrophic disruption of a planetary body the
fragments
move according to their mutual gravitational attraction, finally
resulting into a more or less massive reaccumulation, as well as
into
the formation of binary or multiple systems. In this paper we
analyze
this process by means of the outcomes of the semi-empirical model
of
catastrophic impacts described by Paolicchi et al. (1996) and
applied
to impacts at planetary sizes by Paolicchi et al. (1993) and
Doressoundiram et al. (1997). It is possible to identify the
location
in the parent body of fragments which are going to be
reaccumulated or
ejected, or to form binaries. Moreover, we compare the results of
numerical integrations with three analytical predicting criteria
existing in the literature, as well as with a new one, based on
the
definition of iso-velocity surfaces. We show that: (a) two of the
criteria presented and used in the literature may lead to severe
over-
or underestimates of the amount of reaccumulated mass; (b) the
new
criterion introduced here and the previous one described by Petit
and
Farinella (1993) are capable of giving an accurate estimate in
many
cases, but are less effective when the reaccumulation is limited
and
not strongly concentrated onto a single big attractor; (c) the
region
in the target where the analytic criteria fail is generally the
transition region between escaping and reaccumulating. This is
the same
region where other interesting phenomena, such as the formation
of
binaries, take place. (C) 1999 Elsevier Science Ltd. All rights
reserved.
----------------------------------------
THE CAMBRIDGE-CONFERENCE NETWORK (CCNet)
----------------------------------------
The CCNet is a scholarly electronic network. To
subscribe/unsubscribe,
please contact the moderator Benny J Peiser <b.j.peiser@livjm.ac.uk>.
Information circulated on this network is for scholarly and
educational use only. The attached information may not be copied
or
reproduced for any other purposes without prior permission of the
copyright holders. The fully indexed archive of the CCNet, from
February 1997 on, can be found at http://abob.libs.uga.edu/bobk/cccmenu.html