PLEASE NOTE:


*

CCNet DIGEST, 19 April 1999
---------------------------

(1) MEGA-TSUNAMIS FROM ASTEROIDS AND SLIDES
    Michael Paine <mpaine@tpgi.com.au>

(2) TSUNAMI FROM ASTEROID IMPACTS
    Michael Paine <mpaine@tpgi.com.au>

(3) SUPER SOUND OF SHOOTING STARS
    BBC ONLINE NETWORK, 18 April 1999

(4) ASTROBIOLOGY IN AD ASTRA MAGAZINE
    Keith Cowing <kcowing@reston.com>

(5) PRESOLAR GRAINS IN PRIMITIVE METEORITES
    U. Ott, MAX PLANCK INSTITUT

(6) METEORITES PROVIDE EVIDENCE FOR SHORT-LIVED NUCLIDES
    J.N. Goswami, PHYS RES LAB

(7) COSMOGENIC NUCLIDES IN METEORITES
    R. Michel & S. Neumann, UNIVERSITY OF HANNOVER

(8) COMETARY DUST
    M.L. Sitko et al., UNIVERSITY OF CINCINNATI

(9) FORMATION OF INTERSTELLAR ICES BEHIND SHOCK WAVES
    E.A. Bergin et al., HARVARD SMITHSONIAN CTR ASTROPHYS


==========
(1) MEGA-TSUNAMIS FROM ASTEROIDS AND SLIDES

From Michael Paine <mpaine@tpgi.com.au>

The Tsunami Society is holding a Symposium May 25-27 1999 in Honolulu.
Topics to be covered include: "MEGA-TSUNAMIS FROM ASTEROIDS AND SLIDES"
and "Eltanin Asteroid Impact Tsunami".

See
http://www.geocities.com/CapeCanaveral/Lab/1029/TsunamiSymposium99.html
for details.

Wish I could be there!

Michael Paine

================
(2) TSUNAMI FROM ASTEROID IMPACTS

From Michael Paine <mpaine@tpgi.com.au>

I have (again) reviewed my calculations of the risk to low-lying areas,
based in part on some values for deepwater wave heights published by
Crawford and Mader in 1998 (see abstract at
http://www.ccalmr.ogi.edu/STH/abstracts.html)

I have updated the web page:
http://www1.tpgi.com.au/users/tps-seti/spacegd7.html
Here are some of the concluding lines:

This suggests that tsunami from asteroids with a diameter less than 500m
should only be of concern for locations where the run-up factor is
greater than 20. In all cases it appears that risk of serious tsunami
from Tunguska-style events (50m diameter asteroids) is much less than
for larger objects...

Table 5 - Relative risk of coastal location compared to inland location
   Tsunami Run-up factor      Relative risk due to all types of impact
          0 (inland)                               1
          5                                        9
          10                                      35
          20                                      75
          40                                      170

This tentative analysis suggests that the risk to a low-lying coastal
area from tsunami generated by asteroids is significantly greater than
the risk from a "direct" impact by such objects. The average interval
between such tsunami events is estimated to range from about 70,000
years for a location with a run-up factor of 40 to about  1.3 million
years for a location with a run-up factor of 5. These compare with an
average interval of 12 millions years for a "direct hit". There is,
however, considerable uncertainty about most of the "input values" used
in these estimates and it is also possible that impacts are not
randomly distributed in time. Finally,  it is stressed that the run-up
factor is not the sole issue in determining the destruction caused by a
tsunami.

Comments are most welcome
Regards
Michael Paine

==============
(3) SUPER SOUND OF SHOOTING STARS

From the BBC ONLINE NETWORK, 18 April 1999
http://news.bbc.co.uk/hi/english/sci/tech/newsid_321000/321596.stm

From BBC Science reporter Dr Chris Riley in San Francisco

A Croatian astronomer thinks he has cracked a meteor mystery that has
baffled the scientific world for over two centuries.

He has managed to record what he believes are the illusive,
instantaneous sounds made by shooting stars as they crash through the
Earth's upper atmosphere.

The extraordinary thing about these noises is that the observer on the
ground hears them at the same time as the meteor appears overhead. On
the face of it, this would seem impossible because it would require the
noises to break the sound barrier!

FULL STORY at
http://news.bbc.co.uk/hi/english/sci/tech/newsid_321000/321596.stm

--------------------
(4) ASTROBIOLOGY IN AD ASTRA MAGAZINE

From Keith Cowing <kcowing@reston.com>

Benny:

Given the recent hoopla regarding the looming threat of asteroid
impacts, multi-planet systems being discovered around nearby stars, and
the discovery of improbably gigantic sulfur-eating bacteria
(implications for Io anyone?), I thought you might like to direct your
readers to a special issue (January/February  1999) of the National
Space Society's magazine "Ad Astra" devoted to Astrobiology.

By going to http://www.astrobiology.com/adastra  you'll be able to read
an "expanded" edition of this magazine.  The following articles are
presented in their final form *before* having been edited down to meet
size constraints of the printed issue.  Several of the articles from
this issue are also online at the National Space Society website in
their edited form (as printed) at http://www.nss.org/adastra

------------

* Overview, by Keith Cowing Ad Astra Guest Editor

* Eulogy for Joseph Zelibor, by Rita Collwell, Director, National  Science
  Foundation

* Toilets of the Gods or The Colon-ization of Space, by Sir Arthur C.  Clarke

* Astrobiology 101:Exploring the Living Universe, by Mitchell K.   Hobish
and Keith Cowing

* Ex astra: Life from the Stars:Organic chemistry amidst the stars,  by
Michael Meyer

* It's dead Jim. But was it ever alive? The ALH84001 announcement at   T+2
years: How  well does this piece of Mars meet accepted criteria   for
evidence of ancient life?, by Everett K. Gibson, Jr., David S. McKay,
Kathie Thomas-Keprta, Frances Westall, and Christopher A. Romanek

* The Search for Extremophiles on Earth and Beyond: What is extreme  here
may be just business-as-usual elsewhere, by Penelope Boston

* Bring Em Back Alive -- Or At Least Carefully: Planetary Protection
Provisions for Sample Return Missions, by Margaret S. Race and John D.
Rummel

* Earth Is a Planet, Too! Inhabited Worlds: It takes one to know one, by
Mitchell K. Hobish

* Robots Vs Humans in space: BOTH will be required, by Gregory  Schmidt and
Michael Hawes

-------

Keith Cowing, Webmaster and Editor of:
The Astrobiology Web - http://www.astrobiology.com
NASA Watch - http://www.reston.com/nasa/watch.html

=================
(5) PRESOLAR GRAINS IN PRIMITIVE METEORITES

U. Ott: On laboratory studies of grains from outside the solar system.
PROCEEDINGS OF THE INDIAN ACADEMY OF SCIENCES-EARTH AND PLANETARY
SCIENCES, 1998, Vol.107, No.4, pp.379-390

*) MAX PLANCK INSTITUT FUER CHEMIE,BECHERWEG 27,D-55128 MAINZ,GERMANY

An overview is given of the identified surviving presolar grains in
primitive meteorites. Two of these phases are discussed in more detail:
(a) Presolar silicon carbide, with special emphasis on heavy element
isotopic compositions which trace the slow neutron capture process
(s-process) of nucleosynthesis. It is argued that there are problems
either with the grain or neutron capture cross section data or with
current basic understanding of heavy element nucleosynthesis. (b)
Presolar diamonds, where new developments are discussed concerning the
origin of the (supernova) Xenon-HL component thought to be contained
within them; in addition, arguments are presented in favor of diverse
carrier phases for the various Xe components observed in diamond
separates. Copyright 1999, Institute for Scientific Information Inc.

================
(6) METEORITES PROVIDE EVIDENCE FOR SHORT-LIVED NUCLIDES

J.N. Goswami: Short-lived nuclides in the early solar system.
PROCEEDINGS OF THE INDIAN ACADEMY OF SCIENCES-EARTH AND PLANETARY
SCIENCES, 1998, Vol.107, No.4, pp.401-411

*) PHYS RES LAB,AHMEDABAD 380009,GUJARAT,INDIA

Isotopic records in meteorites provide evidence for the presence of
several short-lived nuclides in the early solar system with half-lives
varying from 10(5) to similar to 8 x 10(7) years. Most of the nuclides
with longer half-life (> 10(7) years) are considered to be products of
stellar nucleosynthesis taking place over long time scales in our
galaxy. However, for the relatively shorter-lived nuclides, two
possibilities exist; they could be products of energetic particle
interactions taking place in a presolar or early solar environment, or,
they could have been produced in a stellar source and injected into the
protosolar molecular cloud just prior to its collapse. The presently
available data appear to support the latter case and put a stringent
constraint of less than a million years for the time scale for the
collapse of the protosolar molecular cloud to form the Sun and some of
the first solar system solids. This short time scale also suggests
the possibility of a triggered origin for the solar system with the
very process of injection of the short-lived nuclides acting as the
trigger for the collapse of the protosolar molecular cloud. Fossil
records of the short-lived nuclides in meteorites also provide very
useful chronological information on the early solar system processes
like the time scale for nebular processing, the time scales for
differentiation and for metal/silicate fractionation within
planetesimals. The currently available data suggest a time scale of a
few million years for nebular processing and a relatively short time
scale of about ten million years within which differentiation,
melting and recrystallization in some of the planetesimals took
place. Copyright 1999, Institute for Scientific Information Inc.

================
(7) COSMOGENIC NUCLIDES IN METEORITES

R. Michel & S. Neumann: Interpretation of cosmogenic nuclides in
meteorites on the basis of accelerator experiments and physical model
calculations. PROCEEDINGS OF THE INDIAN ACADEMY OF SCIENCES-EARTH AND
PLANETARY SCIENCES, 1998, Vol.107, No.4, pp.441-457

*) UNIVERSITY OF HANNOVER,CTR RADIAT PROTECT & RADIOECOL, KLEINEN FELDE
30,D-30167 HANNOVER,GERMANY

Cosmogenic nuclides in extraterrestrial matter provide a wealth of
information on the exposure and collision histories of small objects in
space and on the history of the solar and galactic cosmic radiation.
The interpretation of the observed abundances of cosmogenic nuclides
requires detailed and accurate knowledge of their production rates.
Accelerator experiments provide a quantitative basis and the ground
truth for modeling cosmogenic nuclide production by measurements of the
relevant cross sections and by realistic simulations of the interaction
of galactic protons with meteoroids under completely controlled
conditions, respectively. We review the establishment of physical model
calculations of cosmogenic nuclide production in extraterrestrial
matter on the basis of such accelerator experiments and exemplify this
approach by presenting new experimental and theoretical results for the
cosmogenic nuclide Ti-44. The model calculations describe all aspects
of cosmogenic nuclide production and allow the determination of
long-term solar and galactic cosmic ray spectra and a consistent
interpretation of cosmogenic nuclides in extraterrestrial matter.
Copyright 1999, Institute for Scientific Information Inc.

================
(8) COMETARY DUST

M.L. Sitko*), C.A. Grady, D.K. Lynch, R.W. Russell, M.S. Hanner:
Cometary dust in the debris disks of HD 31648 and HD 163296:
Two 'baby' beta Pictoris stars. ASTROPHYSICAL JOURNAL, 1999, Vol.510,
No.1 Pt1, pp.408-412

*) UNIVERSITY OF CINCINNATI,DEPT PHYS,CINCINNATI,OH,45221

The debris disks surrounding the pre-main-sequence stars HD 31648 and
HD 163296 were observed spectroscopically between 3 and 14 mu m. Both
stars possess a silicate emission Feature at 10 mu m that resembles
that of the star beta Pictoris and those observed in solar system
comets. The structure of the band is consistent with a mixture of
olivine and pyroxene material, plus an underlying continuum of
unspecified origin. The similarity in both size and structure of the
silicate band suggests that the material in these systems had a
processing history similar to that in our own solar system prior to the
time that the grains were incorporated into comets. Copyright 1999,
Institute for Scientific Information Inc.

======================
(9) FORMATION OF INTERSTELLAR ICES BEHIND SHOCK WAVES

E.A. Bergin*), D.A. Neufeld, G.J. Melnick: Formation of interstellar
ices behind shock waves. ASTROPHYSICAL JOURNAL, 1999, Vol.510, No.2
Pt2, pp.L145-L148

*) HARVARD SMITHSONIAN CTR ASTROPHYS,MS-66,60 GARDEN ST,
   CAMBRIDGE,MA,02138

We have used a coupled dynamical and chemical model to examine the
chemical changes induced by the passage of an interstellar shock in
well-shielded regions. Using this model, we demonstrate that the
formation of H2O in a shock will be followed in tb: postshock phase by
depletion of the water molecules onto the grain surfaces. To attempt to
discriminate between the creation of ices behind shocks and their
production by means of grain surface chemistry, we examine title
deuterium chemistry of water before, during, and after a shock. We show
that chemical evolution in the postshock gas can account for both the
deuterium fractionation and the abundance of CO2 relative to H2O
observed in interstellar and cometary ices. Given the pervasiveness of
shocks and turbulent motions within molecular clouds, the model
presented here offers an alternative theory to grain surface chemistry
for the creation of ices in the interstellar medium, ices that may
ultimately be incorporated into comets. Copyright 1999, Institute for
Scientific Information Inc.

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