PLEASE NOTE:
*
CCNet DIGEST, 29 April 1999
---------------------------
(1) NO HARD EVIDENCE FOR SIGNS OF 'LIFE' ON MARS METEORITES
http://helix.nature.com/nsu/990429/990429-6.html
(2) RAS MEETING ON THE SEARCH FOR EXTRATERRESTRIAL LIFE
Jacqueline Mitton <jmitton@dial.pipex.com>
(3) HOW RARE ARE EXTRATERRESTRIAL CIVILIZATIONS, AND WHEN DID
THEY
EMERGE?
M. Livio, SPACE TELESCOPE SCIENCE INSTITUTE
(4) THE ASTONISHING REDNESS OF KUIPER-BELT OBJECTS
N.C. Wickramasinghe & F. Hoyle, CARDIFF
UNIVERSITY
(5) DEVONIAN MASS EXTINCTION: HOW MANY IMPACTS (IF ANY)?
G. Racki, SILESIAN UNIVERSITY
(6) VREDEFORT SHATTER CONES NOT RELATED TO IMPACT EVENT?
L.O. Nicolaysen & W.U. Reimold,
UNIVERRSITY OF WITWATERSRAND
(7) KITCHENER & METEORITE FLUX
Bernd Pauli <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>
(8) HIGH-ACCURACY STATISTICAL SIMULATION OF PLANETARY ACCRETION
S. Inaba et al., TOKYO INSTITUTE OF TECHNOLOGY
=========
(1) NO HARD EVIDENCE FOR SIGNS OF 'LIFE' ON MARS METEORITES
Small spherical object of desire
From http://helix.nature.com/nsu/990429/990429-6.html
By SARA ABDULLA
The announcement of signs of life elsewhere in the Universe --
such as
in meteorites from the planet Mars -- may rest on the
identification of
tiny blobs seen in certain minerals as the remains of things that
once
lived.
Such announcements should be hedged with caution, as demonstrated
in
experiments by Brenda L. Kirkland of the University of Texas,
Austin,
Texas and her colleagues, reporting in the April issue of
Geology. They
have been looking at tiny spherical objects found in samples of
the
carbonate mineral calcite, and show that there is no way to
distinguish
between an organic or inorganic source for the blobs, just by
looking
at them.
These objects, between 25 and 300 nanometres (millionths of a
millimetre) in diameter, and detected by electron microscopy, are
assumed to have made their way into the mineral as it
precipitated from
solution. Because calcite precipitation is in some cases
associated
with the activity of bacteria, some have suggested that the tiny
blobs
are themselves bacteria, albeit of extremely small size.
Even microbiologists, who are used to looking at life on a
miniature
scale, find it hard to conceive of creatures as small as these
purported 'nannobacteria', which often have a volume of only a
thousandth the volume of typical bacteria -- possibly too small
to
support all the necessities of life. Neverthess, miniature
bacteria
only 80 nanometres across do seem to exist. Geologists and
mineralogists, on the other hand, suggest that the blobs reported
from
close-up studies of calcite could just as well be flaws in the
crystal
structure, or inclusions of mineral contaminants, as evidence for
nannobacteria.
The researchers addressed the problem by precipitating calcite
from
solution, and growing calcite crystals, in carefully controlled
laboratory conditions -- with or without bacteria or other
organic
débris. Small spherical objects consistent with the reported
appearance
of nannobacteria appeared in both cases.
This work shows that the appearance of nannobacteria in a calcite
crystal could indicate the presence of organic life -- or it
could not.
It is impossible to tell just by looking at the objects
themselves. In
the case of purported microfossils from Mars, this may be the
best we
can do, and the question will have to remain -- frustratingly --
an
open one.
© Macmillan Magazines Ltd 1999 - NATURE NEWS SERVICE
*****
Alternative origins for nannobacteria-like objects in calcite
Brenda L. Kirkland, F. Leo Lynch, Michael A. Rahnis, Robert L.
Folk,
Department of Geological Sciences, University of Texas, Austin,
Texas
78712, USA
Ian J. Molineux, Department of Microbiology, University of Texas,
Austin, Texas 78712, USA
Robert J. C. McLean, Department of Biology, Southwest Texas State
University, San Marcos, Texas 78666, USA
ABSTRACT
More than 40 calcite-precipitation experiments were performed
under
sterile conditions in order to investigate the origins of 25–300
nm
spherical-, rod-, and ovoid-shaped objects that have been widely
interpreted as evidence of nanometer-scale life (i.e.,
nannobacteria).
Individual experiments included the addition of soluble organic
compounds, common species of eubacteria, or phage-induced
eubacterial
lysates. These experiments indicate that many of the
nanometer-scale
objects have inorganic or nonnannobacterial origins. In the
precipitation experiments, calcite formed euhedral crystals 50–800
nm
in diameter and smaller (<50 nm) anhedral or rounded particles
or
protocrystals. The small anhedral or rounded solids resembled
nannobacteria. The relative amount of anhedral or rounded calcite
was
greatest in experiments with a dissolved organic component. These
controlled experiments are in accord with observations that
rounded
nanometer-scale objects are more common in minerals formed in
organic-rich environments. Bacterial fragments occur as rounded
to
irregularly shaped particles that included cell-wall fragments,
expulsed cytoplasm, and relict capsules that also closely
resembled
nannobacteria. Acid etching of the large euhedral crystals
produced in
the precipitation experiments also resulted in the formation of
nanometer-scale features that resembled nannobacteria in natural
carbonates. The shapes of the etching artifacts vary as a
function of
the strength of the acid and the duration of etching. Much
caution is
advisable in interpreting the origin of rounded features <50
nm.
==============
(2) RAS MEETING ON THE SEARCH FOR EXTRATERRESTRIAL LIFE
ROYAL ASTRONOMICAL SOCIETY
PRESS INFORMATION NOTE
Date: 29 April 1998
Ref. PN 99/11
Issued by: Dr Jacqueline Mitton
RAS Press Officer
Office & home phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@dial.pipex.com
SEARCH FOR EXTRATERRESTRIAL LIFE HIGHLIGHTED AT
ROYAL ASTRONOMICAL SOCIETY MEETING ON MAY 14TH
Current issues in the search for extraterrestrial life will be
the
subject of a half-day discussion meeting in London as part of the
Royal
Astronomical Society's regular monthly programme.
Media representatives are cordially invited to attend as
observers.
Speakers are expected to be available for interview immediately
after
the meeting, or by prior arrangement. (On the day of the meeting,
please use Jacqueline Mitton's mobile phone number 0370 386133.)
An outline of the programme, and contact details for speakers is
given
below.
THE SEARCH FOR EXTRATERRESTRIAL LIFE
Discussion meeting at the
SCIENTIFIC SOCIETIES LECTURE THEATRE
23 SAVILE ROW, LONDON W1
FRIDAY 14th MAY 1998
Organiser: Dr Barrie W. Jones (Open University,
phone: 01908 653378 ,
e-mail: b.w.jones@open.ac.uk)
The search for extraterrestrial life has emerged as one of the
great
scientific quests that will surely dominate the early decades of
the
new millennium. This meeting will explore the likelihood of
finding
potential habitats beyond the Earth, the likelihood that any such
habitats are populated with some form of life, and the likelihood
that
any such life has evolved to become technologically intelligent.
Observational programmes for finding extraterrestrial habitats
and
extraterrestrial life will be described.
10.00 Registration (no fee)/Coffee/Posters
10.30 Dr Don Cowan (University College London, phone: 0171 504
2246, e-mail:
don.cowan@ucl.ac.uk)
"Extremophilic micro-organisms and the search for
exobiology"
This presentation will review the current status of the 'envelope
of
life', and briefly discuss the diversity of extreme habitats
together
with the adaptations of the 'extremophile' organisms that occupy
them.
10.50 Prof. Colin Pillinger (Open University, phone 01908
655049,
e-mail: C.T.Pillinger@open.ac.uk)
"Beagle 2"
The Beagle 2 project, part of the ESA's Mars Express mission,
will land
on our nearest planetary neighbour at the end of 2003. The
lander
carries experiments to look for past life, and to establish
whether the
conditions appropriate to life exist. As part of its programme of
atmospheric analysis it will seek to detect compounds, such as
methane,
which could indicate contemporary life.
11.10 Dr Monica Grady (Natural History Museum, phone: 0171 938
9445,
e-mail m.grady@nhm.ac.uk)
"The outer Solar System: habitable niches
on inhospitable hosts"
In recent years it has become apparent that Europa, and other
satellites of the giant planets, harbour regions on or just
beneath
their surfaces where terrestrial forms of life could survive.
This
raises the possibility that at least some of these regions are
hosts to
extraterrestrial life today.
11.30 Prof. John Papaloizou (Queen Mary and Westfield College,
fax: 0181 983
3522 , e-mail: jcbp@qmw.ac.uk)
"Formation of short period
giant planets, orbital migration
and terrestrial
planets"
Many of the known exoplanets are giants orbiting close to their
stars.
It is believed that these giants formed further out and migrated
inwards. Migration mechanisms will be outlined, and the possible
occurrence of terrestrial planets in such systems considered.
11.50 Dr Alan Penny (Rutherford Appleton Laboratory, phone: 01235
445675, e-mail: alan.penny@rl.ac.uk
)
"Spectroscopic search for life on nearby
exoplanets the future"
ESA's "Darwin" space interferometry mission, a
candidate for a 2012
launch, will be able to take spectra of the atmospheres of
Earth-like
planets orbiting stars up to 50 light-years away. This talk will
describe the effect of life on the atmosphere of an Earth-like
planet,
and how Darwin will be capable of detecting oxygen, a definite
sign of
active life, in a planet's atmosphere.
12.10 Prof. Paul C. W. Davies (Camtech, Australia, e-mail:
pcwd@camtech.net.au.
Contact from 10 to 13 May via Jacqueline Mitton, phone
01223 564914, e-mail: jmitton@dial.pipex.com)
"SETI and biological
determinism"
The SETI project is founded on belief in biological determinism,
i.e.
that life is almost bound to emerge under earthlike conditions.
Proponents of this view claim that life is "written
into" the laws of
physics. However, it isn't. That does not make biological
determinism
wrong, but dependant upon the existence of additional principles
of
organisation.
12.35 Dr Ian Crawford (University College London, phone: 0171 419
3431,
e-mail: iac@star.ucl.ac.uk)
"How common are
extraterrestrial civilisations?"
While life may be common in the Galaxy, the absence of evidence
for
extraterrestrial civilisations means that they are probably very
rare.
This suggests that there is no 'inevitable' evolutionary link
between
the origin of life and the emergence of spacefaring/communicating
civilisations, and it is suggested that the evolution of
multicellularity may be the bottleneck in this process. However,
a
fuller understanding of the cosmic significance of life can only
come
from a greatly enhanced exploration of the universe around us.
12.55 Dr Ian Morison (NRAL, Jodrell Bank, phone: 01477 571321,
e-mail:
im@jb.man.ac.uk)
"Jodrell Bank's role in the Project
Phoenix SETI experiment"
Project Phoenix is the name of the resurrected search for
extraterrestrial intelligence, following the early termination of
the
NASA search a few years ago. The search is conducted by a variety
of
radio telescopes around the world, and constitutes one of the
major
ongoing searches.
13.25 End of meeting
=================
(3) HOW RARE ARE EXTRATERRESTRIAL CIVILIZATIONS, AND WHEN DID
THEY
EMERGE?
M. Livio: How rare are extraterrestrial civilizations, and when
did
they emerge? ASTROPHYSICAL JOURNAL, 1999, Vol.511, No.1 Pt1,
pp.429-431
SPACE TELESCOPE SCIENCE INSTITUTE,3700 SAN MARTIN
DR,BALTIMORE,MD,21218
It is shown that, contrary to an existing claim, the
near-equality
between the lifetime of the Sun and the timescale of biological
evolution on Earth does not necessarily imply that
extraterrestrial
civilizations are exceedingly rare. Furthermore, on the basis of
simple
assumptions it is demonstrated that a near-equality between these
two
timescales may be the most probable relation. A calculation of
the
cosmic history of carbon production that is based on the recently
determined history of the star formation rate suggests that the
most
likely time for intelligent civilizations to emerge in the
universe was
when the universe was already older than about 10 Gyr (for an
assumed
current age of about 13 Gyr). Copyright 1999, Institute for
Scientific
Information Inc.
==============
(4) THE ASTONISHING REDNESS OF KUIPER-BELT OBJECTS
N.C. Wickramasinghe*) & F. Hoyle: The astonishing redness of
Kuiper-belt objects. ASTROPHYSICS AND SPACE SCIENCE, 1998,
Vol.259,
No.2, pp.205-208
*) CARDIFF UNIVERSITY,SCH MATH,POB 926,SENGHENNYDD RD,CARDIFF CF2
4YH,S
GLAM,WALES
The recently reported extreme redness of a class of Kuiper-belt
objects
could be yet another indirect indication of extraterrestrial
microbiology in the outer solar system. Copyright 1999, Institute
for
Scientific Information Inc.
=============
(5) DEVONIAN MASS EXTINCTION: HOW MANY IMPACTS (IF ANY)?
G. Racki: The Frasnian-Famennian biotic crisis: How many (if any)
bolide impacts? GEOLOGISCHE RUNDSCHAU, 1999, Vol.87, No.4,
pp.617-632
SILESIAN UNIVERSITY,DEPT EARTH SCI,PL-41200 SOSNOWIEC,POLAND
The prime causation of the mid-late Devonian mass extinction near
the
Frasnian-Famennian (F-F) boundary remains uncertain.
Nevertheless,
geochemical evidence has been presented recently as decisive
evidence
of a giant bolide impact occurring precisely at the F-F boundary,
which
promoted the global mortality episode. Palaeobiological data,
however,
imply a gradual global change, which is otherwise seen as a
record of
either multiple extraterrestrial catastrophes or of
impact-triggered
Earth-bound mechanisms. Sedimentological (mega-tsunami), physical
(craters, microtektites), and geochemical records remain either
elusive
in many aspects, or incompatible with the predicted impact crisis
pattern. Biotic succession across the F-F horizon is still poorly
known, especially in continental domains, to evidence a
synchronous
('bedding-plane') killing event at the close of the crisis.
Instead,
the commonly documented stepwise loss of biomass and an unproved
distinctive idead zonei are hard to explain simply as sampling
artifacts. The assumed mass mortality precisely at the F-F
boundary may
be limited mainly to the pelagic realm. The underestimated role
of
early Variscan tectonism and associated volcanic-hydrothermal
processes, resulting in thermal and nutrient pulses, as possible
prime
controls of the F-F crisis is suggested, as well as resemblances
to the
superplume-conditioned eventful mid-Cretaceous interval,
exemplified in
the Cenomanian-Turonian mass extinction. Additional shocks,
generated
by minor cometary strikes, are not excluded but may have affected
some
F-F biotas or areas.Copyright 1999, Institute for Scientific
Information Inc.
================
(6) VREDEFORT SHATTER CONES NOT RELATED TO IMPACT EVENT?
L.O. Nicolaysen*) & W.U. Reimold: Vredefort shatter cones
revisited
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 1999, Vol.104,
No.B3,
pp.4911-4930
*) UNIVERRSITY OF WITWATERSRAND,DEPT GEOL,PRIVATE BAG 3,ZA-2050
JOHANNESBURG,SOUTH AFRICA
Shatter cones have been described from a number of circular and
polygonal structures worldwide, the origin of which has been
alternatively ascribed to the impacts of large extraterrestrial
projectiles or to catastrophic endogenic processes. Despite their
association with enigmatic, catastrophic processes, the nature of
shatter cones and the physics involved in their formation have
not been
comprehensively researched. Results of detailed field and
laboratory
studies of shatter cones from three areas in the collar of the
Vredefort Dome in South Africa are presented. Vredefort shatter
cones
are directly related to a widely displayed fracture phenomenon,
termed
'multiply striated joint sets (MSJS)'. MSJs are planar to
curviplanar
fractures occuring at spacings of <1 to several millimeters.
The joint
sets have a fractal character. When a new measurement protocol is
used
in the field, involving study of all joint surfaces and all steps
and
striae exposed on these surfaces, new information is gained on
the
genesis and significance of the MSJS and on their relationship to
striated conical fractures. The internal constitution of a rock
specimen with MSJS was examined in detail, by documenting the
precise
geometry of many fractures in a suite of parallel thin sections
transecting the specimen. The steps and striae on shatter cone
surfaces
have the characteristics of displacement fractures (microfaults),
along
which evidence of melting is observed. Shatter cone and MSJS
surfaces
are often covered with glassy films; we evaluate whether these
fracture
phenomena are linked to the formation of pseudotachylitic
(friction)
melt. Our field and petrographic observations can be interpreted
as
consistent with the generation of shatter cones/MSJS relatively
late in
the formation of the Vredefort structure. This scenario contrasts
sharply with the widely held view that shatter cones are formed
during
the early 'compression' phase of a shock event that affected
horizontal
strata. Copyright 1999, Institute for Scientific Information Inc.
=======================
(7) KITCHENER & METEORITE FLUX
From Bernd Pauli <bernd.pauli@lehrer1.rz.uni-karlsruhe.de>
From Sky & Telescope, June 1999, p. 14:
Fore! I was fascinated by your news note in the February issue*
about a
meteorite that narrowly missed a Canadian golfer. Where better to
look
for fresh meteorites than on a golf course? Is there any large
area of
the Earth's surface that is better looked after or more regularly
searched for small falling objects? In 1991 I wrote a paper on
the
meteorite flux to Earth (Space Science Reviews, Vol. 61, page
275;
1992) indicating that about 60,000 meteorites larger than the
"golf-course meteorite" hit Earth each year. The
fairways on a typical
golf course have a total area about 1.8 x 10^-10 that of Earth.
So each
18-hole golf course has about a 1 in 100,000 chance of being hit
by a
meteorite every year. Multiply this by the number of golf courses
on
Earth, and you realize it's worth encouraging golfers to keep
their
eyes open!
David W. Hughes
Dept. of Physics and Astronomy
University of Sheffield
Sheffield S3 7RH, England
d.hughes@Sheffield.ac.uk
From Sky & Telescope, February 1999, p. 24:
A narrow Meteorite Miss
Scientists are preparing to analyze a meteorite that fell at the
feet
of a Canadian golfer last summer. According to the
Kitchener-Waterloo
Record, Orville Delong was nearly hit by the spacefaring stone on
July
12th last year while golfing in Kitchener, Ontario. The meteorite
is
chondritic, implying an origin in the asteroid belt, says
University of
Toronto geochemist John C. Rucklidge; isotopic analyses performed
shortly after its recovery suggest that it traveled in
interplanetary
space for a minimum of several hundred thousand years. "I’m
deluged by
calls from people who have meteorites that turn out to be
anything
but," Rucklidge continues, but Delong's specimen, with its
black, shiny
surface and fine hairline cracks, is "unlike anything else
you would
ever find." Canadian researchers will slice into the space
rock once a
replica is made.
==============
(8) HIGH-ACCURACY STATISTICAL SIMULATION OF PLANETARY ACCRETION
S. Inaba, H. Tanaka, K. Ohtsuki, K. Nakazawa: High-accuracy
statistical
simulation of planetary accretion: I. Test of the accuracy by
comparison with the solution to the stochastic coagulation
equation.
EARTH PLANETS AND SPACE, 1999, Vol.51, No.3, pp.205-217
*) TOKYO INSTITUTE OF TECHNOLOGY, FAC SCI,DEPT EARTH &
PLANETARY
SCIENCE, TOKYO 1528551,JAPAN
The object of this series of studies is to develop a highly
accurate
statistical code for describing the planetary accumulation
process. In
the present paper, as a first step, we check the validity of the
method
proposed by Wetherill and Stewart (1989) by comparing the results
obtained by their method with the analytical solution to the
stochastic
coagulation equation (or to a well-evaluated numerical solution).
As
the collisional probability Aii between bodies with masses of
im(1) and
jm(1) (m(1) being the unit mass), we consider the two cases: one
is
A(ij) proportional to i x j and another is A(ij) proportional to
min(i,
j)(i(1/3) + j(1/3))(i + j). In both cases, it is known that
runaway
growth occurs. The latter case corresponds to a simplified model
of the
planetesimal accumulation. We assumed that a collision of two
bodies
leads to their coalescence. Wetherill and Stewart's method
contains
some parameters controlling the practical numerical computation.
Among
these, two parameters are important: the mass division parameter
delta,
which determines the mass ratio of the adjacent mass batches, and
the
time division parameter epsilon, which controls the size of a
time step
in numerical integration. Through a number of numerical
simulations for
the case of A(ij) = i x j, we find that when delta less than or
equal
to 1.6 and epsilon less than or equal to 0.03 the numerical
simulation
can reproduce the analytical solution within a certain level of
accuracy independently of the size of the body system. For the
case of
the planetesimal accumulation, it is shown that the simulation
with
delta less than or equal to 1.3 and epsilon less than or equal to
0.04
can describe precisely runaway growth. Because the accumulation
process
is stochastic, in order to obtain reliable mean values it is
necessary
to take the ensemble mean of the numerical results obtained with
different random number generators. It is also found that the
number of
simulations, N-c, demanded to obtain the reliable mean value is
about
500 and does not strongly depend on the functional form of A(ij).
From
the viewpoint of the numerical handling, the above value of delta
(less
than or equal to 1.3) and N-c(similar to 500) are reasonable and,
hence, we conclude that the numerical method proposed by
Wetherill and
Stewart is a valid and useful method for describing the planetary
accumulation process. The real planetary accumulation process is
more
complex since it is coupled with the velocity evolution of the
planetesimals. In the subsequent paper, we will complete the
high-accuracy statistical code which simulate the accumulation
process
coupled with the velocity evolution and test the accuracy of the
code
by comparing with the results of N-body simulation. Copyright
1999,
Institute for Scientific Information Inc.
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