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(meteorobs) Excerpts from "CCNet DIGEST, 19 April 1999"


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From: Benny J Peiser <b.j.peiser@livjm.acdot uk>
To: cambridge-conference@livjm.acdot uk
Subject: CCNet DIGEST, 19 April 1999
Date: Mon, 19 Apr 1999 10:54:42 -0400 (EDT)

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

[...]

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

[...]

(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


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

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

=================

(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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